Java web development as it stands today is dramatically more complicated than it needs to be. Most modern web frameworks in the Java space are over complicated and don't embrace the Don't Repeat Yourself (DRY) principals.
Dynamic frameworks like Rails, Django and TurboGears helped pave the way to a more modern way of thinking about web applications. Grails builds on these concepts and dramatically reduces the complexity of building web applications on the Java platform. What makes it different, however, is that it does so by building on already established Java technology like Spring & Hibernate.
Grails is a full stack framework and attempts to solve as many pieces of the web development puzzle through the core technology and it's associated plug-ins. Included out the box are things like:
- An easy to use Object Relational Mapping (ORM) layer built on Hibernate
- An expressive view technology called Groovy Server Pages (GSP)
- A controller layer built on Spring MVC
- A command line scripting environment built on the Groovy-powered Gant
- An embedded Tomcat container which is configured for on the fly reloading
- Dependency injection with the inbuilt Spring container
- Support for internationalization (i18n) built on Spring's core MessageSource concept
- A transactional service layer built on Spring's transaction abstraction
All of these are made easy to use through the power of the
Groovy language and the extensive use of Domain Specific Languages (DSLs)
This documentation will take you through getting started with Grails and building web applications with the Grails framework.
The first step to getting up and running with Grails is to install the distribution. To do so follow these steps:
- Download a binary distribution of Grails and extract the resulting zip file to a location of your choice
- Set the GRAILS_HOME environment variable to the location where you extracted the zip
- On Unix/Linux based systems this is typically a matter of adding something like the following
export GRAILS_HOME=/path/to/grails to your profile
- On Windows this is typically a matter of setting an environment variable under
My Computer/Advanced/Environment Variables
- Now you need to add the
bin directory to your PATH variable:
- On Unix/Linux base system this can be done by doing a
export PATH="$PATH:$GRAILS_HOME/bin"
- On windows this is done by modifying the
Path environment variable under My Computer/Advanced/Environment Variables
If Grails is working correctly you should now be able to type
grails in the terminal window and see output similar to the below:
Welcome to Grails 1.0 - http://grails.org/
Licensed under Apache Standard License 2.0
Grails home is set to: /Developer/grails-1.0
No script name specified. Use 'grails help' for more info
Although the Grails development team have tried to keep breakages to a minimum there are a number of items to consider when upgrading a Grails 1.0.x or 1.1.x application to Grails 1.2. The major changes are described in detail below.
Upgrading from Grails 1.1.x
Plugin paths
In Grails 1.1.x typically a
pluginContextPath variable was used to establish paths to plugin resources. For example:
<g:resource dir="${pluginContextPath}/images" file="foo.jpg" />In Grails 1.2 views have been made plugin aware and this is no longer necessary:
<g:resource dir="images" file="foo.jpg" />
Additionally the above example will no longer link to an application image from a plugin view. To do so you need to change the above to:
<g:resource contextPath="" dir="images" file="foo.jpg" />
The same rules apply to the
javascript and
renderTag and Body return values
Tags no longer return
java.lang.String instances but instead return a
StreamCharBuffer instance. The
StreamCharBuffer class implements all the same methods as
String, however code like this may break:
def foo = body()
if(foo instanceof String) {
// do something
}In these cases you should use the
java.lang.CharSequence interface, which both
String and
StreamCharBuffer implement:
def foo = body()
if(foo instanceof CharSequence) {
// do something
}New JSONBuilder
There is a new version of
JSONBuilder which is semantically different to earlier versions of Grails. However, if your application depends on the older semantics you can still use the now deprecated implementation by settings the following property to
true in Config.groovy:
grails.json.legacy.builder=true
Validation on Flush
Grails now executes validation routines when the underlying Hibernate session is flushed to ensure that no invalid objects are persisted. If one of your constraints (such as a custom validator) is executing a query then this can cause an addition flush resulting in a
StackOverflowError. Example:
static constraints = {
author(validator: { a ->
assert a != Book.findByTitle("My Book").author
})
}The above code can lead to a
StackOverflowError in Grails 1.2. The solution is to run the query in a new Hibernate
session (which is recommended in general as doing Hibernate work during flushing can cause other issues):
static constraints = {
author(validator: { a ->
Book.withNewSession {
assert a != Book.findByTitle("My Book").author
}
})
}
Upgrading from Grails 1.0.x
Groovy 1.6
Grails 1.1 and above ship with Groovy 1.6 and no longer supports code compiled against Groovy 1.5. If you have a library that is written in Groovy 1.5 you will need to recompile it against Groovy 1.6 before using it with Grails 1.1.
Java 5.0
Grails 1.1 now no longer supports JDK 1.4, if you wish to continue using Grails then it is recommended you stick to the Grails 1.0.x stream until you are able to upgrade your JDK.
Configuration Changes
1) The setting
grails.testing.reports.destDir has been renamed to
grails.project.test.reports.dir for consistency.
2) The following settings have been moved from
grails-app/conf/Config.groovy to
grails-app/conf/BuildConfig.groovy:
grails.config.base.webXmlgrails.war.destFilegrails.war.dependenciesgrails.war.copyToWebAppgrails.war.resources
3) The
grails.war.java5.dependencies option is no longer supported, since Java 5.0 is now the baseline (see above).
4) The use of jsessionid (now considered harmful) is disabled by default. If your application requires jsessionid you can re-enable its usage by adding the following to
grails-app/conf/Config.groovy:
grails.views.enable.jsessionid=true
5) The syntax used to configure Log4j has changed. See the user guide section on
Logging for more information.
Plugin Changes
Since 1.1, Grails no longer stores plugins inside your
PROJECT_HOME/plugins directory by default. This may result in compilation errors in your application unless you either re-install all your plugins or set the following property in
grails-app/conf/BuildConfig.groovy:
grails.project.plugins.dir="./plugins"
Script Changes
1) If you were previously using Grails 1.0.3 or below the following syntax is no longer support for importing scripts from GRAILS_HOME:
Ant.property(environment:"env")
grailsHome = Ant.antProject.properties."env.GRAILS_HOME"includeTargets << new File ( "${grailsHome}/scripts/Bootstrap.groovy" )Instead you should use the new
grailsScript method to import a named script:
includeTargets << grailsScript( "Bootstrap.groovy" )
2) Due to an upgrade to Gant all references to the variable
Ant should be changed to
ant.
3) The root directory of the project is no long on the classpath, the result is that loading a resource like this will no longer work:
def stream = getClass().classLoader.getResourceAsStream("grails-app/conf/my-config.xml")Instead you should use the Java File APIs with the
basedir property:
new File("${basedir}/grails-app/conf/my-config.xml").withInputStream { stream ->
// read the file
}Command Line Changes
The
run-app-https and
run-war-https commands no longer exist and have been replaced by an argument to
run-app:
Data Mapping Changes
1) Enum types are now mapped using their String value rather than the ordinal value. You can revert to the old behavior by changing your mapping as follows:
static mapping = {
someEnum enumType:"ordinal"
}2) Bidirectional one-to-one associations are now mapped with a single column on the owning side and a foreign key reference. You shouldn't need to change anything, however you may want to drop the column on the inverse side as it contains duplicate data.
REST Support
Incoming XML requests are now no longer automatically parsed. To enable parsing of REST requests you can do so using the
parseRequest argument inside a URL mapping:
"/book"(controller:"book",parseRequest:true)
Alternatively, you can use the new
resource argument, which enables parsing by default:
To create a Grails application you first need to familiarize yourself with the usage of the
grails command which is used in the following manner:
In this case the command you need to execute is
create-app:
grails create-app helloworld
This will create a new directory inside the current one that contains the project. You should now navigate to this directory in terminal:
cd helloworld
To implement the typical "hello world!" example run the
create-controller command:
grails create-controller hello
This will create a new controller (Refer to the section on
Controllers for more information) in the
grails-app/controllers directory called
HelloController.groovy.
Controllers are capable of dealing with web requests and to fulfil the "hello world!" use case our implementation needs to look like the following:
class HelloController {
def world = {
render "Hello World!"
}
}Job done. Now start-up the container with another new command called
run-app:
grails run-app
This will start-up a server on port 8080 and you should now be able to access your application with the URL:
http://localhost:8080/helloworldThe result will look something like the following screenshot:
This is the Grails intro page which is rendered by the
web-app/index.gsp file. You will note it has a detected the presence of your controller and clicking on the link to our controller we can see the text "Hello World!" printed to the browser window.
IntelliJ IDEA
IntelliJ IDEA and the
JetGroovy plug-in offer good support for Groovy & Grails developer. Refer to the section on
Groovy and Grails support on the JetBrains website for a feature overview.
To integrate Grails 1.2 to with IntelliJ run the following command to generate appropriate project files:
grails integrate-with --intellij
NetBeans
A good Open Source alternative is Sun's NetBeans, which provides a Groovy/Grails plugin that automatically recognizes Grails projects and provides the ability to run Grails applications in the IDE, code completion and integration with Sun's Glassfish server. For an overview of features see the
NetBeans Integration guide on the Grails website which was written by the NetBeans team.
Eclipse
We recommend that users of
Eclipse looking to develop Grails application take a look at
SpringSource Tool Suite, which offers built in support for Grails including automatic classpath management, a GSP editor and quick access to Grails commands. See the
STS Integration page for an overview.
TextMate
Since Grails' focus is on simplicity it is often possible to utilize more simple editors and
TextMate on the Mac has an excellent Groovy/Grails bundle available from the
Texmate bundles SVN.
To integrate Grails 1.2 to with TextMate run the following command to generate appropriate project files:
grails integrate-with --textmate
Alternatively TextMate can easily open any project with its command line integration by issuing the following command from the root of your project:
Grails uses "convention over configuration" to configure itself. This typically means that the name and location of files is used instead of explicit configuration, hence you need to familiarize yourself with the directory structure provided by Grails.
Here is a breakdown and links to the relevant sections:
grails-app - top level directory for Groovy sourcesscripts - Gant scripts.src - Supporting sources
groovy - Other Groovy sourcesjava - Other Java sources
test - Unit and integration tests.
Grails applications can be run with the built in Tomcat server using the
run-app command which will load a server on port 8080 by default:
You can specify a different port by using the
server.port argument:
grails -Dserver.port=8090 run-app
More information on the
run-app command can be found in the reference guide.
The
create-* commands in Grails automatically create integration tests for you within the
test/integration directory. It is of course up to you to populate these tests with valid test logic, information on which can be found in the section on
Testing. However, if you wish to execute tests you can run the
test-app command as follows:
Grails also automatically generates an Ant
build.xml which can also run the tests by delegating to Grails'
test-app command:
This is useful when you need to build Grails applications as part of a continuous integration platform such as CruiseControl.
Grails applications are deployed as Web Application Archives (WAR files), and Grails includes the
war command for performing this task:
This will produce a WAR file in the root of your project which can then be deployed as per your containers instructions.
NEVER deploy Grails using the run-app command as this command sets Grails up for auto-reloading at runtime which has a severe performance and scalability implication
When deploying Grails you should always run your containers JVM with the
-server option and with sufficient memory allocation. A good set of VM flags would be:
Grails runs on any Servlet 2.4 and above container and is known to work on the following specific container products:
- Tomcat 5.5
- Tomcat 6.0
- SpringSource tc Server
- SpringSource dm Server 1.0
- GlassFish v1 (Sun AS 9.0)
- GlassFish v2 (Sun AS 9.1)
- GlassFish v3 Prelude
- Sun App Server 8.2
- Websphere 6.1
- Websphere 5.1
- Resin 3.2
- Oracle AS
- JBoss 4.2
- Jetty 6.1
- Jetty 5
- Weblogic 7/8/9/10
Some containers have bugs however, which in most cases can be worked around. A
list of known deployment issues can be found on the Grails wiki.
To get started quickly with Grails it is often useful to use a feature called
Scaffolding to generate the skeleton of an application. To do this use one of the
generate-* commands such as
generate-all, which will generate a
controller and the relevant
views:
Grails ships with a few convenience targets such as
create-controller,
create-domain-class and so on that will create
Controllers and different artefact types for you.
These are merely for your convenience and you can just as easily use an IDE or your favourite text editor.
For example to create the basis of an application you typically need a
domain model:
grails create-domain-class book
This will result in the creation of a domain class at
grails-app/domain/Book.groovy such as:
There are many such
create-* commands that can be explored in the command line reference guide.
It may seem odd that in a framework that embraces "convention-over-configuration" that we tackle this topic now, but since what configuration there is typically a one off, it is best to get it out the way.
With Grails' default settings you can actually develop and application without doing any configuration whatsoever. Grails ships with an embedded container and in-memory HSQLDB meaning there isn't even a database to set-up.
However, typically you want to set-up a real database at some point and the way you do that is described in the following section.
For general configuration Grails provides a file called
grails-app/conf/Config.groovy. This file uses Groovy's
ConfigSlurper which is very similar to Java properties files except it is pure Groovy hence you can re-use variables and use proper Java types!
You can add your own configuration in here, for example:
Then later in your application you can access these settings in one of two ways. The most common is via the
GrailsApplication object, which is available as a variable in controllers and tag libraries:
assert "world" == grailsApplication.config.foo.bar.hello
The other way involves getting a reference to the
ConfigurationHolder class that holds a reference to the configuration object:
import org.codehaus.groovy.grails.commons.*
…
def config = ConfigurationHolder.config
assert "world" == config.foo.bar.hello
Grails also provides the following configuration options:
grails.config.locations - The location of properties files or addition Grails Config files that should be merged with main configurationgrails.enable.native2ascii - Set this to false if you do not require native2ascii conversion of Grails i18n properties filesgrails.views.default.codec - Sets the default encoding regime for GSPs - can be one of 'none', 'html', or 'base64' (default: 'none'). To reduce risk of XSS attacks, set this to 'html'.grails.views.gsp.encoding - The file encoding used for GSP source files (default is 'utf-8')grails.mime.file.extensions - Whether to use the file extension to dictate the mime type in Content Negotiationgrails.mime.types - A map of supported mime types used for Content Negotiationgrails.serverURL - A string specifying the server URL portion of absolute links, including server name e.g. grails.serverURL="http://my.yourportal.com". See createLink.
War generation
grails.war.destFile - Sets the location where the war command should place the generated WAR filegrails.war.dependencies - A closure containing Ant builder syntax or a list of JAR filenames. Allows you to customise what libaries are included in the WAR file.grails.war.java5.dependencies - A list of the JARs that should be included in the WAR file for JDK 1.5 and above.grails.war.copyToWebApp - A closure containing Ant builder syntax that is legal inside an Ant copy, for example "fileset()". Allows you to control what gets included in the WAR file from the "web-app" directory.grails.war.resources - A closure containing Ant builder syntax. Allows the application to do any other pre-warring stuff it needs to.
For more information on using these options, see the section on
deployment
Logging Basics
Grails uses its common configuration mechanism to configure the underlying
Log4j log system. To configure logging you must modify the file
Config.groovy located in the
grails-app/conf directory.
This single
Config.groovy file allows you to specify separate logging configurations for
development,
test, and
production environments. Grails processes the
Config.groovy and configures Log4j appropriately.
Since 1.1 Grails provides a Log4j DSL, that you can use to configure Log4j an example of which can be seen below:
log4j = {
error 'org.codehaus.groovy.grails.web.servlet', // controllers
'org.codehaus.groovy.grails.web.pages' // GSP warn 'org.mortbay.log'
}Essentially, each method translates into a log level and you can pass the names of the packages you want to log at that level as arguments to the method.
Some useful loggers include:
org.codehaus.groovy.grails.commons - Core artefact information such as class loading etc.org.codehaus.groovy.grails.web - Grails web request processingorg.codehaus.groovy.grails.web.mapping - URL mapping debuggingorg.codehaus.groovy.grails.plugins - Log plugin activityorg.springframework - See what Spring is doingorg.hibernate - See what Hibernate is doing
The Root Logger
The Root logger is the logger that all other loggers inherit from. You can configure the Root logger using the root method:
root {
error()
additivity = true
}The above example configures the root logger to log messages at the error level and above to the default standard out appender. You can also configure the root logger to log to one or more named appenders:
appenders {
file name:'file', file:'/var/logs/mylog.log'
}
root {
debug 'stdout', 'file'
additivity = true
}Here the root logger will log to two appenders - the default 'stdout' appender and a 'file' appender.
You can also configure the root logger from the argument passed into the Log4J closure:
log4j = { root ->
root.level = org.apache.log4j.Level.DEBUG
…
}
The closure argument "root" is an instance of
org.apache.log4j.Logger , so refer to the API documentation for Log4J to find out what properties and methods are available to you.
Custom Appenders
Using the Log4j you can define custom appenders. The following appenders are available by default:
jdbc - An appender that logs to a JDBC connectionconsole - An appender that logs to standard outfile - An appender that logs to a filerollingFile - An appender that logs to rolling set of files
For example to configure a rolling file appender you can do:
log4j = {
appenders {
rollingFile name:"myAppender", maxFileSize:1024, file:"/tmp/logs/myApp.log"
}
}Each argument passed to the appender maps to a property of underlying
Appender class. The example above sets the
name,
maxFileSize and
file properties of the
RollingFileAppender class.
If you prefer to simply create the appender programmatically yourself, or you have your own appender implementation then you can simply call the
appender method and appender instance:
import org.apache.log4j.*log4j = {
appenders {
appender new RollingFileAppender(name:"myAppender", maxFileSize:1024, file:"/tmp/logs/myApp.log")
}
}You can then log to a particular appender by passing the name as a key to one of the log level methods from the previous section:
error myAppender:"org.codehaus.groovy.grails.commons"
Custom Layouts
By default the Log4j DSL assumes that you want to use a
PatternLayout. However, there are other layouts available including:
xml - Create an XML log filehtml - Creates an HTML log filesimple - A simple textual logpattern - A Pattern layout
You can specify custom patterns to an appender using the
layout setting:
log4j = {
appenders {
console name:'customAppender', layout:pattern(conversionPattern: '%c{2} %m%n')
}
}This also works for the built-in appender "stdout", which logs to the console:
log4j = {
appenders {
console name:'stdout', layout:pattern(conversionPattern: '%c{2} %m%n')
}
}Full stacktraces
When exceptions occur, there can be an awful lot of noise in the stacktrace from Java and Groovy internals. Grails filters these typically irrelevant details and restricts traces to non-core Grails/Groovy class packages.
When this happens, the full trace is always written to the
StackTrace logger. This logs to a file called
stacktrace.log - but you can change this in your
Config.groovy to do anything you like. For example if you prefer full stack traces to go to standard out you can add this line:
error stdout:"StackTrace"
You can completely disable stacktrace filtering by setting the
grails.full.stacktrace VM property to
true:
grails -Dgrails.full.stacktrace=true run-app
Logging by Convention
All application artefacts have a dynamically added
log property. This includes
domain classes,
controllers, tag libraries and so on. Below is an example of its usage:
def foo = "bar"
log.debug "The value of foo is $foo"
Logs are named using the convention
grails.app.<artefactType>.ClassName. Below is an example of how to configure logs for different Grails artefacts:
log4j = {
// Set level for all application artefacts
info "grails.app"
// Set for a specific controller
debug "grails.app.controller.YourController"
// Set for a specific domain class
debug "grails.app.domain.Book"
// Set for all taglibs
info "grails.app.tagLib"}The artefacts names are dictated by convention, some of the common ones are listed below:
bootstrap - For bootstrap classesdataSource - For data sourcestagLib - For tag librariesservice - For service classescontroller - For controllersdomain - For domain entities
Grails provides the following GORM configuration options:
grails.gorm.failOnError - If set to true, causes the save() method on domain classes to throw a grails.validation.ValidationException if validation fails during a save. This option may also be assigned a list of Strings representing package names. If the value is a list of Strings then the failOnError behavior will only be applied to domain classes in those packages (including sub-packages). See the save method docs for more information.
Enable failOnError for all domain classes…
grails.gorm.failOnError=true
Enable failOnError for domain classes by package…
grails.gorm.failOnError = ['com.companyname.somepackage', 'com.companyname.someotherpackage']
grails.gorm.autoFlush = If set to true, causes the merge, save and delete methods to flush the session, replacing the need to do something like save(flush: true).
Per Environment Configuration
Grails supports the concept of per environment configuration. Both the
Config.groovy file and the
DataSource.groovy file within the
grails-app/conf directory can take advantage of per environment configuration using the syntax provided by
ConfigSlurper As an example consider the following default
DataSource definition provided by Grails:
dataSource {
pooled = false
driverClassName = "org.hsqldb.jdbcDriver"
username = "sa"
password = ""
}
environments {
development {
dataSource {
dbCreate = "create-drop" // one of 'create', 'createeate-drop','update'
url = "jdbc:hsqldb:mem:devDB"
}
}
test {
dataSource {
dbCreate = "update"
url = "jdbc:hsqldb:mem:testDb"
}
}
production {
dataSource {
dbCreate = "update"
url = "jdbc:hsqldb:file:prodDb;shutdown=true"
}
}
}Notice how the common configuration is provided at the top level and then an
environments block specifies per environment settings for the
dbCreate and
url properties of the
DataSource. This syntax can also be used within
Config.groovy.
Packaging and Running for Different Environments
Grails'
command line has built in capabilities to execute any command within the context of a specific environment. The format is:
grails [environment] [command name]
In addition, there are 3 preset environments known to Grails:
dev,
prod, and
test for
development,
production and
test. For example to create a WAR for the
test environment you could do:
If you have other environments that you need to target you can pass a
grails.env variable to any command:
grails -Dgrails.env=UAT run-app
Programmatic Environment Detection
Within your code, such as in a Gant script or a bootstrap class you can detect the environment using the
Environment class:
import grails.util.Environment...switch(Environment.current) {
case Environment.DEVELOPMENT:
configureForDevelopment()
break
case Environment.PRODUCTION:
configureForProduction()
break
}Per Environment Bootstrapping
Its often desirable to run code when your application starts up on a per-environment basis. To do so you can use the
grails-app/conf/BootStrap.groovy file's support for per-environment execution:
def init = { ServletContext ctx ->
environments {
production {
ctx.setAttribute("env", "prod")
}
development {
ctx.setAttribute("env", "dev")
}
}
ctx.setAttribute("foo", "bar")
}Generic Per Environment Execution
The previous
BootStrap example uses the
grails.util.Environment class internally to execute. You can also use this class yourself to execute your own environment specific logic:
Environment.executeForCurrentEnvironment {
production {
// do something in production
}
development {
// do something only in development
}
}Since Grails is built on Java technology to set-up a data source requires some knowledge of JDBC (the technology that doesn't stand for Java Database Connectivity).
Essentially, if you are using another database other than HSQLDB you need to have a JDBC driver. For example for MySQL you would need
Connector/JDrivers typically come in the form of a JAR archive. Drop the JAR into your projects
lib directory.
Once you have the JAR in place you need to get familiar Grails' DataSource descriptor file located at
grails-app/conf/DataSource.groovy. This file contains the dataSource definition which includes the following settings:
driverClassName - The class name of the JDBC driverusername - The username used to establish a JDBC connectionpassword - The password used to establish a JDBC connectionurl - The JDBC URL of the databasedbCreate - Whether to auto-generate the database from the domain model or notpooled - Whether to use a pool of connections (defaults to true)logSql - Enable SQL loggingdialect - A String or Class that represents the Hibernate dialect used to communicate with the database. See the org.hibernate.dialect package for available dialects.properties - Extra properties to set on the DataSource bean. See the Commons DBCP BasicDataSource documentation.
A typical configuration for MySQL may be something like:
dataSource {
pooled = true
dbCreate = "update"
url = "jdbc:mysql://localhost/yourDB"
driverClassName = "com.mysql.jdbc.Driver"
username = "yourUser"
password = "yourPassword"
}
When configuring the DataSource do not include the type or the def keyword before any of the configuration settings as Groovy will treat these as local variable definitions and they will not be processed. For example the following is invalid:
dataSource {
boolean pooled = true // type declaration results in local variable
…
}
Example of advanced configuration using extra properties:
dataSource {
pooled = true
dbCreate = "update"
url = "jdbc:mysql://localhost/yourDB"
driverClassName = "com.mysql.jdbc.Driver"
username = "yourUser"
password = "yourPassword"
properties {
maxActive = 50
maxIdle = 25
minIdle = 5
initialSize = 5
minEvictableIdleTimeMillis = 60000
timeBetweenEvictionRunsMillis = 60000
maxWait = 10000
}
}The previous example configuration assumes you want the same config for all environments: production, test, development etc.
Grails' DataSource definition is "environment aware", however, so you can do:
dataSource {
// common settings here
}
environments {
production {
dataSource {
url = "jdbc:mysql://liveip.com/liveDb"
}
}
}Since many Java EE containers typically supply
DataSource instances via the
Java Naming and Directory Interface (JNDI). Sometimes you are required to look-up a
DataSource via JNDI.
Grails supports the definition of JNDI data sources as follows:
dataSource {
jndiName = "java:comp/env/myDataSource"
}The format on the JNDI name may vary from container to container, but the way you define the
DataSource remains the same.
The
dbCreate property of the
DataSource definition is important as it dictates what Grails should do at runtime with regards to automatically generating the database tables from
GORM classes. The options are:
create-drop - Drop and re-create the database when Grails is runcreate - Create the database if it doesn't exist, but don't modify it if it does. Deletes existing data.update - Create the database if it doesn't exist, and modify it if it does exist
Both create-drop and create will destroy all existing data hence use with caution!
In
development mode
dbCreate is by default set to "create-drop":
dataSource {
dbCreate = "create-drop" // one of 'create', 'create-drop','update'
}What this does is automatically drop and re-create the database tables on each restart of the application. Obviously this may not be what you want in production.
Although Grails does not currently support Rails-style Migrations out of the box, there are currently three plugins that provide similar capabilities to Grails: Autobase (http://wiki.github.com/RobertFischer/autobase), The LiquiBase plugin and the DbMigrate plugin both of which are available via the grails list-plugins command
The default configuration file
Config.groovy in
grails-app/conf is fine in the majority of cases, but there may be circumstances where you want to maintain the configuration in a file
outside the main application structure. For example if you are deploying to a WAR some administrators prefer the configuration of the application to be externalized to avoid having to re-package the WAR due to a change of configuration.
In order to support deployment scenarios such as these the configuration can be externalized. To do so you need to point Grails at the locations of the configuration files Grails should be using by adding a
grails.config.locations setting in
Config.groovy:
grails.config.locations = [ "classpath:${appName}-config.properties",
"classpath:${appName}-config.groovy",
"file:${userHome}/.grails/${appName}-config.properties",
"file:${userHome}/.grails/${appName}-config.groovy"]In the above example we're loading configuration files (both Java properties files and
ConfigSlurper configurations) from different places on the classpath and files located in
USER_HOME.
Ultimately all configuration files get merged into the
config property of the
GrailsApplication object and are hence obtainable from there.
Grails also supports the concept of property place holders and property override configurers as defined in Spring For more information on these see the section on Grails and Spring
Versioning Basics
Grails has built in support for application versioning. When you first create an application with the
create-app command the version of the application is set to
0.1. The version is stored in the application meta data file called
application.properties in the root of the project.
To change the version of your application you can run the
set-version command:
The version is used in various commands including the
war command which will append the application version to the end of the created WAR file.
Detecting Versions at Runtime
You can detect the application version using Grails' support for application metadata using the
GrailsApplication class. For example within
controllers there is an implicit
grailsApplication variable that can be used:
def version = grailsApplication.metadata['app.version']
If it is the version of Grails you need you can use:
def grailsVersion = grailsApplication.metadata['app.grails.version']
or the
GrailsUtil class:
import grails.util.*
def grailsVersion = GrailsUtil.grailsVersion
Since Grails 1.2, the documentation engine that powers the creation of this documentation is available to your Grails projects.
The documentation engine uses a variation on the Textile syntax to automatically create project documentation with smart linking, formatting etc.
Creating project documentation
To use the engine you need to follow a few conventions. Firstly you need to create a
src/docs/guide directory and then have numbered text files using the
gdoc format. For example:
+ src/docs/guide/1. Introduction.gdoc
+ src/docs/guide/2. Getting Started.gdoc
The title of each chapter is taken from the file name. The order is dictated by the numerical value at the beginning of the file name.
Creating reference items
Reference items appear in the left menu on the documentation and are useful for quick reference documentation. Each reference item belongs to a category and a category is a directory located in the
src/docs/ref directory. For example say you defined a new method called
renderPDF, that belongs to a category called
Controllers this can be done by creating a gdoc text file at the following location:
+ src/ref/Controllers/renderPDF.gdoc
Configuring Output Properties
There are various properties you can set within your
grails-app/conf/Config.groovy file that customize the output of the documentation such as:
- grails.doc.authors - The authors of the documentation
- grails.doc.license - The license of the software
- grails.doc.copyright - The copyright message to display
- grails.doc.footer - The footer to use
Other properties such as the name of the documentation and the version are pulled from your project itself.
Generating Documentation
Once you have created some documentation (refer to the syntax guide in the next chapter) you can generate an HTML version of the documentation using the command:
This command will output an
docs/manual/index.html which can be opened to view your documentation.
Documentation Syntax
As mentioned the syntax is largely similar to Textile or Confluence style wiki markup. The following sections walk you through the syntax basics.
Basic Formatting
Monospace:
monospace
Italic:
italic Bold:
bold
Image:
!http://grails.org/images/new/grailslogo_topNav.png!
Linking
There are several ways to create links with the documentation generator. A basic external link can either be defined using confluence or textile style markup:
[SpringSource|http://www.springsource.com/] or "SpringSource":http://www.springsource.com/
For links to other sections inside the user guide you can use the
guide: prefix:
[Intro|guide:1. Introduction]
The documentation engine will warn you if any links to sections in your guide break. Sometimes though it is preferable not to hard code the actual names of guide sections since you may move them around. To get around this you can create an alias inside
grails-app/conf/Config.groovy:
grails.doc.alias.intro="1. Introduction"
And then the link becomes:
This is useful since if you linked the to "1. Introduction" chapter many times you would have to change all of those links.
To link to reference items you can use a special syntax:
In this case the category of the reference item is on the left hand side of the | and the name of the reference item on the right.
Finally, to link to external APIs you can use the
api: prefix. For example:
[String|api:java.lang.String]
The documentation engine will automatically create the appropriate javadoc link in this case. If you want to add additional APIs to the engine you can configure them in
grails-app/conf/Config.groovy. For example:
grails.doc.api.org.hibernate="http://docs.jboss.org/hibernate/stable/core/api"
The above example configures classes within the
org.hibernate package to link to the Hibernate website's API docs.
Lists and Headings
Headings can be created by specifying the letter 'h' followed by a number and then a dot:
h3.<space>Heading3
h4.<space>Heading4
Unordered lists are defined with the use of the * character:
* item 1
** subitem 1
** subitem 2
* item 2
Numbered lists can be defined with the # character:
Tables can be created using the
table macro:
| Name | Number |
|---|
| Albert | 46 |
| Wilma | 1348 |
| James | 12 |
{table}
*Name* | *Number*
Albert | 46
Wilma | 1348
James | 12
{table}Code and Notes
You can define code blocks with the
code macro:
class Book {
String title
}{code}
class Book {
String title
}
{code}The example above provides syntax highlighting for Java and Groovy code, but you can also highlight XML markup:
{code:xml}
<hello>world</hello>
{code}There are also a couple of macros for displaying notes and warnings:
Note:
This is a note!
{note}
This is a note!
{note}Warning:
This is a warning!
{warning}
This is a warning!
{warning}In order to control how JAR dependencies are resolved Grails features (since version 1.2) a dependency resolution DSL that allows you to control how dependencies for applications and plugins are resolved.
Inside the
grails-app/conf/BuildConfig.groovy file you can specify a
grails.project.dependency.resolution property that configures how dependencies are resolved:
grails.project.dependency.resolution = {
// config here
}The default configuration looks like the following:
grails.project.dependency.resolution = {
inherits "global" // inherit Grails' default dependencies
log "warn" // log level of Ivy resolver, either 'error', 'warn', 'info', 'debug' or 'verbose'
repositories {
grailsHome() // uncomment the below to enable remote dependency resolution
// from public Maven repositories
//mavenCentral()
//mavenRepo "http://snapshots.repository.codehaus.org"
//mavenRepo "http://repository.codehaus.org"
//mavenRepo "http://download.java.net/maven/2/"
//mavenRepo "http://repository.jboss.com/maven2/
}
dependencies {
// specify dependencies here under either 'build', 'compile', 'runtime', 'test' or 'provided' scopes eg.
// runtime 'com.mysql:mysql-connector-java:5.1.5'
}}The details of the above will be explained in the next few sections.
Grails features 5 dependency resolution configurations (or 'scopes') which you can take advantage of:
-
build: Dependencies for the build system only
-
compile: Dependencies for the compile step
-
runtime: Dependencies needed at runtime but not for compilation (see above)
-
test: Dependencies needed for testing but not at runtime (see above)
-
provided: Dependencies needed at development time, but not during WAR deployment
Within the
dependencies block you can specify a dependency that falls into one of these configurations by calling the equivalent method. For example if your application requires the MySQL driver to function at
runtime you can specify as such:
runtime 'com.mysql:mysql-connector-java:5.1.5'
The above uses the string syntax which is
group:name:version. You can also use a map-based syntax:
runtime group:'com.mysql', name:'mysql-connector-java', version:'5.1.5'
Multiple dependencies can be specified by passing multiple arguments:
runtime 'com.mysql:mysql-connector-java:5.1.5',
'net.sf.ehcache:ehcache:1.6.1'// Orruntime(
[group:'com.mysql', name:'mysql-connector-java', version:'5.1.5'],
[group:'net.sf.ehcache', name:'ehcache', version:'1.6.1']
)
Remote Repositories
Grails, when installed, does not use any remote public repositories. There is a default
grailsHome() repository that will locate the JAR files Grails needs from your Grails installation. If you want to take advantage of a public repository you need to specify as such inside the
repositories block:
repositories {
mavenCentral()
}In this case the default public Maven repository is specified. To use the SpringSource Enterprise Bundle Repository you can use the
ebr() method:
You can also specify a specific Maven repository to use by URL:
repositories {
mavenRepo "http://repository.codehaus.org"
}Local Resolvers
If you do not wish to use a public Maven repository you can specify a flat file repository:
repositories {
flatDir name:'myRepo', dirs:'/path/to/repo'
}Custom Resolvers
If all else fails since Grails builds on Apache Ivy you can specify an Ivy resolver:
repositories {
resolver new URLResolver(...)
}Authentication
If your repository requires some form of authentication you can specify as such using a
credentials block:
credentials {
realm = ".."
host = "localhost"
username = "myuser"
password = "mypass"
}The above can also be placed in your
USER_HOME/.grails/settings.groovy file using the
grails.project.ivy.authentication setting:
grails.project.ivy.authentication = {
credentials {
realm = ".."
host = "localhost"
username = "myuser"
password = "mypass"
}
}If you are having trouble getting a dependency to resolve you can enable more verbose debugging from the underlying engine using the
log method:
// log level of Ivy resolver, either 'error', 'warn', 'info', 'debug' or 'verbose'
log "warn"
By default every Grails application inherits a bunch of framework dependencies. This is done through the line:
Inside the
BuildConfig.groovy file. If you wish exclude certain inherited dependencies then you can do so using the
excludes method:
inherits("global") {
excludes "oscache", "ehcache"
}Most Grails applications will have runtime dependencies on a lot of jar files that are provided by the Grails framework. These
include libraries like Spring, Sitemesh, Hibernate etc. When a war file is created, all of these dependencies will be included
in it. But, an application may choose to exclude these jar files from the war. This is useful when the jar files will
be provided by the container, as would normally be the case if multiple Grails applications are deployed to the same container.
The dependency resolution DSL provides a mechanism to express that all of the default dependencies will be provided by the container.
This is done by invoking the
defaultDependenciesProvided method and passing
true as an argument:
grails.project.dependency.resolution = { defaultDependenciesProvided true // all of the default dependencies will be "provided" by the container inherits "global" // inherit Grails' default dependencies repositories {
grailsHome()
// …
}
dependencies {
// …
}
}Note that
defaultDependenciesProvided must come before
inherits, otherwise the Grails dependencies will be included in the war.
As mentioned in the previous section a Grails application consists of dependencies inherited from the framework, the plugins installed and the application dependencies itself.
To obtain a report of an application's dependencies you can run the
dependency-report command:
This will output a report to the
target/dependency-report directory by default. You can specify which configuration (scope) you want a report for by passing an argument containing the configuration name:
grails dependency-report runtime
Specifying Plugin JAR dependencies
The way in which you specify dependencies for a
plugin is identical to how you specify dependencies in an application. When a plugin is installed into an application the application automatically inherits the dependencies of the plugin.
If you want to define a dependency that is resolved for use with the plugin but not
exported to the application then you can set the
exported property of the dependency:
compile( 'org.hibernate:hibernate-core:3.3.1.GA') {
exported = false
}In this can the
hibernate-core dependency will be available only to the plugin and not resolved as an application dependency.
Overriding Plugin JAR Dependencies in Your Application
If a plugin is using a JAR which conflicts with another plugin, or an application dependency then you can override how a plugin resolves its dependencies inside an application using the
plugin method:
plugin("hibernate") {
compile( 'org.hibernate:hibernate-core:3.3.1.GA') {
excludes 'ehcache', 'xml-apis', 'commons-logging'
}
compile 'org.hibernate:hibernate-annotations:3.4.0.GA',
'org.hibernate:hibernate-commons-annotations:3.3.0.ga' runtime 'javassist:javassist:3.4.GA'
}In this case the application is controlling how the
hibernate plugin resolves dependencies and not the
hibernate plugin. If you wish to simply exclude a single dependency resolved by a plugin then you can do so:
plugin("hibernate") {
runtime "cglib:cglib-nodep:2.1_3"
excludes 'javassist:javassist:3.4.GA'
}When using the Grails Maven plugin, Grails' dependency resolution mechanics are disabled as it is assumed that you will manage dependencies via Maven's
pom.xml file.
However, if you would like to continue using Grails regular commands like run-app, test-app and so on then you can tell Grails' command line to load dependencies from the Maven
pom.xml file instead.
To do so simply add the following line to your
BuildConfig.groovy:
grails.project.dependency.resolution = {
pom true
..
}The line
pom true tells Grails to parse Maven's
pom.xml and load dependencies from there.
Grails' command line system is built on
Gant - a simple Groovy wrapper around
Apache Ant.
However, Grails takes it a bit further through the use of convention and the
grails command. When you type:
Grails does a search in the following directories for Gant scripts to execute:
USER_HOME/.grails/scriptsPROJECT_HOME/scriptsPROJECT_HOME/plugins/*/scriptsGRAILS_HOME/scripts
Grails will also convert command names that are in lower case form such as run-app into camel case. So typing
Results in a search for the following files:
USER_HOME/.grails/scripts/RunApp.groovyPROJECT_HOME/scripts/RunApp.groovyPLUGINS_HOME/*/scripts/RunApp.groovyGLOBAL_PLUGINS_HOME/*/scripts/RunApp.groovyGRAILS_HOME/scripts/RunApp.groovy
If multiple matches are found Grails will give you a choice of which one to execute. When Grails executes a Gant script, it invokes the "default" target defined in that script. If there is no default, Grails will quit with an error.
To get a list and some help about the available commands type:
Which outputs usage instructions and the list of commands Grails is aware of:
Usage (optionals marked with *):
grails [environment]* [target] [arguments]*Examples:
grails dev run-app
grails create-app booksAvailable Targets (type grails help 'target-name' for more info):
grails bootstrap
grails bug-report
grails clean
grails compile
...
Refer to the Command Line reference in left menu of the reference guide for more information about individual commands
You can create your own Gant scripts by running the
create-script command from the root of your project. For example the following command:
grails create-script compile-sources
Will create a script called
scripts/CompileSources.groovy. A Gant script itself is similar to a regular Groovy script except that it supports the concept of "targets" and dependencies between them:
target(default:"The default target is the one that gets executed by Grails") {
depends(clean, compile)
}
target(clean:"Clean out things") {
ant.delete(dir:"output")
}
target(compile:"Compile some sources") {
ant.mkdir(dir:"mkdir")
ant.javac(srcdir:"src/java", destdir:"output")
}As demonstrated in the script above, there is an implicit
ant variable that allows access to the
Apache Ant API.
In previous versions of Grails (1.0.3 and below), the variable was Ant, i.e. with a capital first letter.
You can also "depend" on other targets using the
depends method demonstrated in the
default target above.
The default target
In the example above, we specified a target with the explicit name "default". This is one way of defining the default target for a script. An alternative approach is to use the
setDefaultTarget() method:
target("clean-compile": "Performs a clean compilation on the app's source files.") {
depends(clean, compile)
}
target(clean:"Clean out things") {
ant.delete(dir:"output")
}
target(compile:"Compile some sources") {
ant.mkdir(dir:"mkdir")
ant.javac(srcdir:"src/java", destdir:"output")
}setDefaultTarget("clean-compile")This allows you to call the default target directly from other scripts if you wish. Also, although we have put the call to
setDefaultTarget() at the end of the script in this example, it can go anywhere as long as it comes
after the target it refers to ("clean-compile" in this case).
Which approach is better? To be honest, you can use whichever you prefer - there don't seem to be any major advantages in either case. One thing we would say is that if you want to allow other scripts to call your "default" target, you should move it into a shared script that doesn't have a default target at all. We'll talk some more about this in the next section.
Grails ships with a lot of command line functionality out of the box that you may find useful in your own scripts (See the command line reference in the reference guide for info on all the commands). Of particular use are the
compile,
package and
bootstrap scripts.
The
bootstrap script for example allows you to bootstrap a Spring
ApplicationContext instance to get access to the data source and so on (the integration tests use this):
includeTargets << grailsScript("_GrailsBootstrap")target ('default': "Load the Grails interactive shell") {
depends( configureProxy, packageApp, classpath, loadApp, configureApp ) Connection c
try {
// do something with connection
c = appCtx.getBean('dataSource').getConnection()
}
finally {
c?.close()
}
}Pulling in targets from other scripts
Gant allows you to pull in all targets (except "default") from another Gant script. You can then depend upon or invoke those targets as if they had been defined in the current script. The mechanism for doing this is the
includeTargets property. Simply "append" a file or class to it using the left-shift operator:
includeTargets << new File("/path/to/my/script.groovy")
includeTargets << gant.tools.Ivy
Don't worry too much about the syntax using a class, it's quite specialised. If you're interested, look into the Gant documentation.
Core Grails targets
As you saw in the example at the beginning of this section, you use neither the File- nor the class-based syntax for
includeTargets when including core Grails targets. Instead, you should use the special
grailsScript() method that is provided by the Grails command launcher (note that this is not available in normal Gant scripts, just Grails ones).
The syntax for the
grailsScript() method is pretty straightforward: simply pass it the name of the Grails script you want to include, without any path information. Here is a list of Grails scripts that you may want to re-use:
| Script | Description |
|---|
| _GrailsSettings | You really should include this! Fortunately, it is included automatically by all other Grails scripts bar one (_GrailsProxy), so you usually don't have to include it explicitly. |
| _GrailsEvents | If you want to fire events, you need to include this. Adds an event(String eventName, List args) method. Again, included by almost all other Grails scripts. |
| _GrailsClasspath | Sets up compilation, test, and runtime classpaths. If you want to use or play with them, include this script. Again, included by almost all other Grails scripts. |
| _GrailsProxy | If you want to access the internet, include this script so that you don't run into problems with proxies. |
| _GrailsArgParsing | Provides a parseArguments target that does what it says on the tin: parses the arguments provided by the user when they run your script. Adds them to the argsMap property. |
| _GrailsTest | Contains all the shared test code. Useful if you want to add any extra tests. |
| _GrailsRun | Provides all you need to run the application in the configured servlet container, either normally (runApp/runAppHttps) or from a WAR file (runWar/runWarHttps). |
There are many more scripts provided by Grails, so it is worth digging into the scripts themselves to find out what kind of targets are available. Anything that starts with an "_" is designed for re-use.
In pre-1.1 versions of Grails, the "_Grails..." scripts were not available. Instead, you typically include the corresponding command script, for example "Init.groovy" or "Bootstrap.groovy".Also, in pre-1.0.4 versions of Grails you cannot use the grailsScript() method. Instead, you must use includeTargets << new File(...) and specify the script's location in full (i.e. $GRAILS_HOME/scripts).
Script architecture
You maybe wondering what those underscores are doing in the names of the Grails scripts. That is Grails' way of determining that a script is _internal_, or in other words that it has not corresponding "command". So you can't run "grails _grails-settings" for example. That is also why they don't have a default target.
Internal scripts are all about code sharing and re-use. In fact, we recommend you take a similar approach in your own scripts: put all your targets into an internal script that can be easily shared, and provide simple command scripts that parse any command line arguments and delegate to the targets in the internal script. Say you have a script that runs some functional tests - you can split it like this:
./scripts/FunctionalTests.groovy:includeTargets << new File("${basedir}/scripts/_FunctionalTests.groovy")target(default: "Runs the functional tests for this project.") {
depends(runFunctionalTests)
}./scripts/_FunctionalTests.groovy:includeTargets << grailsScript("_GrailsTest")target(runFunctionalTests: "Run functional tests.") {
depends(...)
…
}Here are a few general guidelines on writing scripts:
- Split scripts into a "command" script and an internal one.
- Put the bulk of the implementation in the internal script.
- Put argument parsing into the "command" script.
- To pass arguments to a target, create some script variables and initialise them before calling the target.
- Avoid name clashes by using closures assigned to script variables instead of targets. You can then pass arguments direct to the closures.
Grails provides the ability to hook into scripting events. These are events triggered during execution of Grails target and plugin scripts.
The mechanism is deliberately simple and loosely specified. The list of possible events is not fixed in any way, so it is possible to hook into events triggered by plugin scripts, for which there is no equivalent event in the core target scripts.
Defining event handlers
Event handlers are defined in scripts called
_Events.groovy. Grails searches for these scripts in the following locations:
USER_HOME/.grails/scripts - user-specific event handlersPROJECT_HOME/scripts - applicaton-specific event handlersPLUGINS_HOME/*/scripts - plugin-specific event handlersGLOBAL_PLUGINS_HOME/*/scripts - event handlers provided by global plugins
Whenever an event is fired,
all the registered handlers for that event are executed. Note that the registration of handlers is performed automatically by Grails, so you just need to declare them in the relevant
_Events.groovy file.
In versions of Grails prior to 1.0.4, the script was called Events.groovy, that is without the leading underscore.
Event handlers are blocks defined in
_Events.groovy, with a name beginning with "event". The following example can be put in your /scripts directory to demonstrate the feature:
eventCreatedArtefact = { type, name ->
println "Created $type $name"
}eventStatusUpdate = { msg ->
println msg
}eventStatusFinal = { msg ->
println msg
}You can see here the three handlers
eventCreatedArtefact,
eventStatusUpdate,
eventStatusFinal. Grails provides some standard events, which are documented in the command line reference guide. For example the
compile command fires the following events:
CompileStart - Called when compilation starts, passing the kind of compile - source or testsCompileEnd - Called when compilation is finished, passing the kind of compile - source or tests
Triggering events
To trigger an event simply include the Init.groovy script and call the event() closure:
includeTargets << grailsScript("_GrailsEvents")event("StatusFinal", ["Super duper plugin action complete!"])Common Events
Below is a table of some of the common events that can be leveraged:
| Event | Parameters | Description |
|---|
| StatusUpdate | message | Passed a string indicating current script status/progress |
| StatusError | message | Passed a string indicating an error message from the current script |
| StatusFinal | message | Passed a string indicating the final script status message, i.e. when completing a target, even if the target does not exit the scripting environment |
| CreatedArtefact | artefactType,artefactName | Called when a create-xxxx script has completed and created an artefact |
| CreatedFile | fileName | Called whenever a project source filed is created, not including files constantly managed by Grails |
| Exiting | returnCode | Called when the scripting environment is about to exit cleanly |
| PluginInstalled | pluginName | Called after a plugin has been installed |
| CompileStart | kind | Called when compilation starts, passing the kind of compile - source or tests |
| CompileEnd | kind | Called when compilation is finished, passing the kind of compile - source or tests |
| DocStart | kind | Called when documentation generation is about to start - javadoc or groovydoc |
| DocEnd | kind | Called when documentation generation has ended - javadoc or groovydoc |
| SetClasspath | rootLoader | Called during classpath initialization so plugins can augment the classpath with rootLoader.addURL(...). Note that this augments the classpath after event scripts are loaded so you cannot use this to load a class that your event script needs to import, although you can do this if you load the class by name. |
| PackagingEnd | none | Called at the end of packaging (which is called prior to the Tomcat server being started and after web.xml is generated) |
Grails is most definitely an opinionated framework and it prefers convention to configuration, but this doesn't mean you
can't configure it. In this section, we look at how you can influence and modify the standard Grails build.
The defaults
In order to customise a build, you first need to know
what you can customise. The core of the Grails build configuration is the
grails.util.BuildSettings class, which contains quite a bit of useful information. It controls where classes are compiled to, what dependencies the application has, and other such settings.
Here is a selection of the configuration options and their default values:
| Property | Config option | Default value |
|---|
| grailsWorkDir | grails.work.dir | $USER_HOME/.grails/<grailsVersion> |
| projectWorkDir | grails.project.work.dir | <grailsWorkDir>/projects/<baseDirName> |
| classesDir | grails.project.class.dir | <projectWorkDir>/classes |
| testClassesDir | grails.project.test.class.dir | <projectWorkDir>/test-classes |
| testReportsDir | grails.project.test.reports.dir | <projectWorkDir>/test/reports |
| resourcesDir | grails.project.resource.dir | <projectWorkDir>/resources |
| projectPluginsDir | grails.plugins.dir | <projectWorkDir>/plugins |
| globalPluginsDir | grails.global.plugins.dir | <grailsWorkDir>/global-plugins |
| verboseCompile | grails.project.compile.verbose | false |
The
BuildSettings class has some other properties too, but they should be treated as read-only:
| Property | Description |
|---|
| baseDir | The location of the project. |
| userHome | The user's home directory. |
| grailsHome | The location of the Grails installation in use (may be null). |
| grailsVersion | The version of Grails being used by the project. |
| grailsEnv | The current Grails environment. |
| compileDependencies | A list of compile-time project dependencies as File instances. |
| testDependencies | A list of test-time project dependencies as File instances. |
| runtimeDependencies | A list of runtime-time project dependencies as File instances. |
Of course, these properties aren't much good if you can't get hold of them. Fortunately that's easy to do: an instance of
BuildSettings is available to your scripts via the
grailsSettings script variable. You can also access it from your code by using the
grails.util.BuildSettingsHolder class, but this isn't recommended.
Overriding the defaults
All of the properties in the first table can be overridden by a system property or a configuration option - simply use the "config option" name. For example, to change the project working directory, you could either run this command:
grails -Dgrails.project.work.dir=work compile
or add this option to your
grails-app/conf/BuildConfig.groovy file:
grails.project.work.dir = "work"
Note that the default values take account of the property values they depend on, so setting the project working directory like this would also relocate the compiled classes, test classes, resources, and plugins.
What happens if you use both a system property and a configuration option? Then the system property wins because it takes precedence over the
BuildConfig.groovy file, which in turn takes precedence over the default values.
The
BuildConfig.groovy file is a sibling of
grails-app/conf/Config.groovy - the former contains options that only affect the build, whereas the latter contains those that affect the application at runtime. It's not limited to the options in the first table either: you will find build configuration options dotted around the documentation, such as ones for specifying the port that the embedded servlet container runs on or for determining what files get packaged in the WAR file.
Available build settings
| Name | Description |
|---|
| grails.server.port.http | Port to run the embedded servlet container on ("run-app" and "run-war"). Integer. |
| grails.server.port.https | Port to run the embedded servlet container on for HTTPS ("run-app https" and "run-war https"). Integer. |
| grails.config.base.webXml | Path to a custom web.xml file to use for the application (alternative to using the web.xml template). |
| grails.compiler.dependencies | Legacy approach to adding extra dependencies to the compiler classpath. Set it to a closure containing "fileset()" entries. |
| grails.testing.patterns | A list of Ant path patterns that allow you to control which files are included in the tests. The patterns should not include the test case suffix, which is set by the next property. |
| grails.testing.nameSuffix | By default, tests are assumed to have a suffix of "Tests". You can change it to anything you like but setting this option. For example, another common suffix is "Test". |
| grails.war.destFile | A string containing the file path of the generated WAR file, along with its full name (include extension). For example, "target/my-app.war". |
| grails.war.dependencies | A closure containing "fileset()" entries that allows you complete control over what goes in the WAR's "WEB-INF/lib" directory. |
| grails.war.copyToWebApp | A closure containing "fileset()" entries that allows you complete control over what goes in the root of the WAR. It overrides the default behaviour of including everything under "web-app". |
| grails.war.resources | A closure that takes the location of the staging directory as its first argument. You can use any Ant tasks to do anything you like. It is typically used to remove files from the staging directory before that directory is jar'd up into a WAR. |
| grails.project.web.xml | The location to generate Grails' web.xml to |
If all the other projects in your team or company are built using a standard build tool such as Ant or Maven, you become the black sheep of the family when you use the Grails command line to build your application. Fortunately, you can easily integrate the Grails build system into the main build tools in use today (well, the ones in use in Java projects at least).
Ant Integration
When you create a Grails application via the
create-app command, Grails automatically creates an
Apache Ant build.xml file for you containing the following targets:
clean - Cleans the Grails applicationcompile - Compiles your application's source codetest - Runs the unit testsrun - Equivalent to "grails run-app"war - Creates a WAR filedeploy - Empty by default, but can be used to implement automatic deployment
Each of these can be run by Ant, for example:
The build file is all geared up to use
Apache Ivy for dependency management, which means that it will automatically download all the requisite Grails JAR files and other dependencies on demand. You don't even have to install Grails locally to use it! That makes it particularly useful for continuous integration systems such as
CruiseControl or
HudsonIt uses the Grails
Ant task to hook into the existing Grails build system. The task allows you to run any Grails script that's available, not just the ones used by the generated build file. To use the task, you must first declare it:
<taskdef name="grailsTask"
classname="grails.ant.GrailsTask"
classpathref="grails.classpath"/>This raises the question: what should be in "grails.classpath"? The task itself is in the "grails-bootstrap" JAR artifact, so that needs to be on the classpath at least. You should also include the "groovy-all" JAR. With the task defined, you just need to use it! The following table shows you what attributes are available:
| Attribute | Description | Required |
|---|
| home | The location of the Grails installation directory to use for the build. | Yes, unless classpath is specified. |
| classpathref | Classpath to load Grails from. Must include the "grails-bootstrap" artifact and should include "grails-scripts". | Yes, unless home is set or you use a classpath element. |
| script | The name of the Grails script to run, e.g. "TestApp". | Yes. |
| args | The arguments to pass to the script, e.g. "-unit -xml". | No. Defaults to "". |
| environment | The Grails environment to run the script in. | No. Defaults to the script default. |
| includeRuntimeClasspath | Advanced setting: adds the application's runtime classpath to the build classpath if true. | No. Defaults to true. |
The task also supports the following nested elements, all of which are standard Ant path structures:
classpath - The build classpath (used to load Gant and the Grails scripts).compileClasspath - Classpath used to compile the application's classes.runtimeClasspath - Classpath used to run the application and package the WAR. Typically includes everything in @compileClasspath.testClasspath - Classpath used to compile and run the tests. Typically includes everything in runtimeClasspath.
How you populate these paths is up to you. If you are using the
home attribute and put your own dependencies in the
lib directory, then you don't even need to use any of them. For an example of their use, take a look at the generated Ant build file for new apps.
Maven Integration
From 1.1 onwards, Grails provides integration with
Maven 2 via a Maven plugin. The current Maven plugin is based on, but effectively supercedes, the version created by
Octo, who did a great job.
Preparation
In order to use the new plugin, all you need is Maven 2 installed and set up. This is because
you no longer need to install Grails separately to use it with Maven!
The Maven 2 integration for Grails has been designed and tested for Maven 2.0.9 and above. It will not work with earlier versions.
To make life easier for you, we do recommend that you add a plugin group for Grails to your Maven settings file (
$USER_HOME/.m2/settings.xml ):
<settings>
…
<pluginGroups>
<pluginGroup>org.grails</pluginGroup>
</pluginGroups>
</settings>In addition, if you have the Octo Maven Tools for Grails set up then you'll need to remove the
com.octo.mtg plugin group.
Creating a Grails Maven Project
To create a Mavenized Grails project simple run the following command:
mvn archetype:generate -DarchetypeGroupId=org.grails \
-DarchetypeArtifactId=grails-maven-archetype \
-DarchetypeVersion=1.0 \
-DarchetypeRepository=http://snapshots.repository.codehaus.org \
-DgroupId=example -DartifactId=my-appChoose whichever group ID and artifact ID you want for your application, but everything else must be as written. This will create a new Maven project with a POM and a couple of other files. What you won't see is anything that looks like a Grails application. So, the next step is to create the project structure that you're used to:
Now you have a Grails application all ready to go. The plugin integrates into the standard build cycle, so you can use the standard Maven phases to build and package your app:
mvn clean ,
mvn compile ,
mvn test ,
mvn package .
You can also take advantage of some of the Grails commands that have been wrapped as Maven goals:
Mavenizing an existing project
Creating a new project is great way to start, but what if you already have one? You don't want to create a new project and then copy the contents of the old one over. The solution is to create a POM for the existing project using this Maven command:
mvn grails:create-pom -DgroupId=com.mycompany
When this command has finished, you can immediately start using the standard phases, such as
mvn package. Note that you have to specify a group ID when creating the POM.
Adding Grails commands to phases
The standard POM created for you by Grails already attaches the appropriate core Grails commands to their corresponding build phases, so "compile" goes in the "compile" phase and "war" goes in the "package" phase. That doesn't help though when you want to attach a plugin's command to a particular phase. The classic example is functional tests. How do you make sure that your functional tests (using which ever plugin you have decided on) are run during the "integration-test" phase?
Fear not: all things are possible. In this case, you can associate the command to a phase using an extra "execution" block:
<plugin>
<groupId>org.grails</groupId>
<artifactId>grails-maven-plugin</artifactId>
<version>1.0-SNAPSHOT</version>
<extensions>true</extensions>
<executions>
<execution>
<goals>
…
</goals>
</execution>
<execution>
<id>functional-tests</id>
<phase>integration-test</phase>
<goals>
<goal>exec</goal>
</goals>
<configuration>
<command>functional-tests</command>
</configuration>
</execution>
</executions>
</plugin>This also demonstrates the
grails:exec goal, which can be used to run any Grails command. Simply pass the name of the command as the
command system property, and optionally specify the arguments via the
args property:
mvn grails:exec -Dcommand=create-webtest -Dargs=Book
Domain classes are core to any business application. They hold state about business processes and hopefully also implement behavior. They are linked together through relationships, either one-to-one or one-to-many.
GORM is Grails' object relational mapping (ORM) implementation. Under the hood it uses Hibernate 3 (an extremely popular and flexible open source ORM solution) but because of the dynamic nature of Groovy, the fact that it supports both static and dynamic typing, and the convention of Grails there is less configuration involved in creating Grails domain classes.
You can also write Grails domain classes in Java. See the section on Hibernate Integration for how to write Grails domain classes in Java but still use dynamic persistent methods. Below is a preview of GORM in action:
def book = Book.findByTitle("Groovy in Action")book
.addToAuthors(name:"Dierk Koenig")
.addToAuthors(name:"Guillaume LaForge")
.save()A domain class can be created with the
create-domain-class command:
grails create-domain-class Person
This will create a class at the location
grails-app/domain/Person.groovy such as the one below:
If you have the dbCreate property set to "update", "create" or "create-drop" on your DataSource, Grails will automatically generated/modify the database tables for you.
You can customize the class by adding properties:
class Person {
String name
Integer age
Date lastVisit
}Once you have a domain class try and manipulate it via the
shell or
console by typing:
This loads an interactive GUI where you can type Groovy commands.
Try performing some basic CRUD (Create/Read/Update/Delete) operations.
Create
To create a domain class use the Groovy new operator, set its properties and call
save:
def p = new Person(name:"Fred", age:40, lastVisit:new Date())
p.save()
The
save method will persist your class to the database using the underlying Hibernate ORM layer.
Read
Grails transparently adds an implicit
id property to your domain class which you can use for retrieval:
def p = Person.get(1)
assert 1 == p.id
This uses the
get method that expects a database identifier to read the
Person object back from the db.
You can also load an object in a read-only state by using the
read method:
In this case the underlying Hibernate engine will not do any dirty checking and the object will not be persisted. Note that
if you explicitly call the
save method then the object is placed back into a read-write state.
Update
To update an instance, set some properties and then simply call
save again:
def p = Person.get(1)
p.name = "Bob"
p.save()
Delete
To delete an instance use the
delete method:
def p = Person.get(1)
p.delete()
When building Grails applications you have to consider the problem domain you are trying to solve. For example if you were building an
Amazon bookstore you would be thinking about books, authors, customers and publishers to name a few.
These are modeled in GORM as Groovy classes so a
Book class may have a title, a release date, an ISBN number and so on. The next few sections show how to model the domain in GORM.
To create a domain class you can run the
create-domain-class target as follows:
grails create-domain-class Book
The result will be a class at
grails-app/domain/Book.groovy:
If you wish to use packages you can move the Book.groovy class into a sub directory under the domain directory and add the appropriate package declaration as per Groovy (and Java's) packaging rules.
The above class will map automatically to a table in the database called
book (the same name as the class). This behaviour is customizable through the
ORM Domain Specific LanguageNow that you have a domain class you can define its properties as Java types. For example:
class Book {
String title
Date releaseDate
String ISBN
}Each property is mapped to a column in the database, where the convention for column names is all lower case separated by underscores. For example
releaseDate maps onto a column
release_date. The SQL types are auto-detected from the Java types, but can be customized via
Constraints or the
ORM DSL.
Relationships define how domain classes interact with each other. Unless specified explicitly at both ends, a relationship exists only in the direction it is defined.
A one-to-one relationship is the simplest kind, and is defined trivially using a property of the type of another domain class. Consider this example:
Example A
class Face {
Nose nose
}
class Nose {
}In this case we have unidirectional many-to-one relationship from
Face to
Nose. To make it a true one-to-one you should make
nose unique:
class Face {
Nose nose
static constraints = {
nose unique:true
}
}
class Nose {
}To make this relationship bidirectional define the other side as follows:
Example B
class Face {
Nose nose
}
class Nose {
static belongsTo = [face:Face]
}In this case we use the
belongsTo setting to say that
Nose "belongs to" Face. The result of this is that we can create a Face and save it and the database updates/inserts will be
cascaded down to
Nose:
new Face(nose:new Nose()).save()
The example above will save both face and nose. Note that the inverse
is not true and will result in an error due to a transient
Face:
new Nose(face:new Face()).save() // will cause an error
Another important implication of
belongsTo is that if you delete a
Face instance the
Nose will be deleted too:
def f = Face.get(1)
f.delete() // both Face and Nose deleted
In the previous example the foreign key associated the
Face with the
Nose is stored in the parent as column called
nose_id. If you want the foreign key to be stored in the child you need a
hasOne association:
Example C
class Face {
static hasOne = [nose:Nose]
}
class Nose {
Face face
}In this example you get a bidirectional one-to-one where the foreign key column is stored in the
nose table inside a column called
face_id.
A one-to-many relationship is when one class, example
Author, has many instances of a another class, example
Book. With Grails you define such a relationship with the
hasMany setting:
class Author {
static hasMany = [ books : Book ] String name
}
class Book {
String title
}In this case we have a unidirectional one-to-many. Grails will, by default, map this kind of relationship with a join table.
The ORM DSL allows mapping unidirectional relationships using a foreign key association instead
Grails will automatically inject a property of type
java.util.Set into the domain class based on the
hasMany setting. This can be used to iterate over the collection:
def a = Author.get(1)a.books.each {
println it.title
}
The default fetch strategy used by Grails is "lazy", which means that the collection will be lazily initialized. This can lead to the n+1 problem if you are not careful.If you need "eager" fetching you can use the ORM DSL or specify eager fetching as part of a query
The default cascading behaviour is to cascade saves and updates, but not deletes unless a
belongsTo is also specified:
class Author {
static hasMany = [ books : Book ] String name
}
class Book {
static belongsTo = [author:Author]
String title
}If you have two properties of the same type on the many side of a one-to-many you have to use
mappedBy to specify which the collection is mapped:
class Airport {
static hasMany = [flights:Flight]
static mappedBy = [flights:"departureAirport"]
}
class Flight {
Airport departureAirport
Airport destinationAirport
}This is also true if you have multiple collections that map to different properties on the many side:
class Airport {
static hasMany = [outboundFlights:Flight, inboundFlights:Flight]
static mappedBy = [outboundFlights:"departureAirport", inboundFlights:"destinationAirport"]
}
class Flight {
Airport departureAirport
Airport destinationAirport
}Grails supports many-to-many relationships by defining a
hasMany on both sides of the relationship and having a
belongsTo on the owned side of the relationship:
class Book {
static belongsTo = Author
static hasMany = [authors:Author]
String title
}
class Author {
static hasMany = [books:Book]
String name
}Grails maps a many-to-many using a join table at the database level. The owning side of the relationship, in this case
Author, takes responsibility for persisting the relationship and is the only side that can cascade saves across.
For example this will work and cascade saves:
new Author(name:"Stephen King")
.addToBooks(new Book(title:"The Stand"))
.addToBooks(new Book(title:"The Shining"))
.save()
However the below will only save the
Book and not the authors!
new Book(name:"Groovy in Action")
.addToAuthors(new Author(name:"Dierk Koenig"))
.addToAuthors(new Author(name:"Guillaume Laforge"))
.save()
This is the expected behaviour as, just like Hibernate, only one side of a many-to-many can take responsibility for managing the relationship.
Grails' Scaffolding feature does not currently support many-to-many relationship and hence you must write the code to manage the relationship yourself
As well as associations between different domain classes, GORM also supports mapping of basic collection types.
For example, the following class creates a
nicknames association that is a
Set of
String instances:
class Person {
static hasMany = [nicknames:String]
}GORM will map an association like the above using a join table. You can alter various aspects of how the join table is mapped using the
joinTable argument:
class Person {
static hasMany = [nicknames:String] static mapping = {
hasMany joinTable:[name:'bunch_o_nicknames', key:'person_id', column:'nickname', type:"text"]
}
}The example above will map to a table that looks like the following:
bunch_o_nicknames Table
---------------------------------------------
| person_id | nickname |
---------------------------------------------
| 1 | Fred |
---------------------------------------------
As well as
association, Grails supports the notion of composition. In this case instead of mapping classes onto separate tables a class can be "embedded" within the current table. For example:
class Person {
Address homeAddress
Address workAddress
static embedded = ['homeAddress', 'workAddress']
}
class Address {
String number
String code
}The resulting mapping would looking like this:
If you define the Address class in a separate Groovy file in the grails-app/domain directory you will also get an address table. If you don't want this to happen use Groovy's ability to define multiple classes per file and include the Address class below the Person class in the grails-app/domain/Person.groovy file
GORM supports inheritance both from abstract base classes and concrete persistent GORM entities. For example:
class Content {
String author
}
class BlogEntry extends Content {
URL url
}
class Book extends Content {
String ISBN
}
class PodCast extends Content {
byte[] audioStream
}In the above example we have a parent
Content class and then various child classes with more specific behaviour.
Considerations
At the database level Grails by default uses table-per-hierarchy mapping with a discriminator column called
class so the parent class (
Content) and its sub classes (
BlogEntry,
Book etc.), share the
same table.
Table-per-hierarchy mapping has a down side in that you
cannot have non-nullable properties with inheritance mapping. An alternative is to use table-per-subclass which can be enabled via the
ORM DSLHowever, excessive use of inheritance and table-per-subclass can result in poor query performance due to the excessive use of join queries. In general our advice is if you're going to use inheritance, don't abuse it and don't make your inheritance hierarchy too deep.
Polymorphic Queries
The upshot of inheritance is that you get the ability to polymorphically query. For example using the
list method on the
Content super class will return all sub classes of
Content:
def content = Content.list() // list all blog entries, books and pod casts
content = Content.findAllByAuthor('Joe Bloggs') // find all by authordef podCasts = PodCast.list() // list only pod castsSets of objects
By default when you define a relationship with GORM it is a
java.util.Set which is an unordered collection that cannot contain duplicates. In other words when you have:
class Author {
static hasMany = [books:Book]
}The books property that GORM injects is a
java.util.Set. The problem with this is there is no ordering when accessing the collection, which may not be what you want. To get custom ordering you can say that the set is a
SortedSet:
class Author {
SortedSet books
static hasMany = [books:Book]
}In this case a
java.util.SortedSet implementation is used which means you have to implement
java.lang.Comparable in your Book class:
class Book implements Comparable {
String title
Date releaseDate = new Date() int compareTo(obj) {
releaseDate.compareTo(obj.releaseDate)
}
}The result of the above class is that the Book instances in the books collections of the Author class will be ordered by their release date.
Lists of objects
If you simply want to be able to keep objects in the order which they were added and to be able to reference them by index like an array you can define your collection type as a
List:
class Author {
List books
static hasMany = [books:Book]
}In this case when you add new elements to the books collection the order is retained in a sequential list indexed from 0 so you can do:
author.books[0] // get the first book
The way this works at the database level is Hibernate creates a
books_idx column where it saves the index of the elements in the collection in order to retain this order at the db level.
When using a
List, elements must be added to the collection before being saved, otherwise Hibernate will throw an exception (
org.hibernate.HibernateException: null index column for collection):
// This won't work!
def book = new Book(title: 'The Shining')
book.save()
author.addToBooks(book)// Do it this way instead.
def book = new Book(title: 'Misery')
author.addToBooks(book)
author.save()
Maps of Objects
If you want a simple map of string/value pairs GORM can map this with the following:
class Author {
Map books // map of ISBN:book names
}def a = new Author()
a.books = ["1590597583":"Grails Book"]
a.save()
In this case the key and value of the map MUST be strings.
If you want a Map of objects then you can do this:
class Book {
Map authors
static hasMany = [authors:Author]
}def a = new Author(name:"Stephen King")def book = new Book()
book.authors = [stephen:a]
book.save()The static
hasMany property defines the type of the elements within the Map. The keys for the map
must be strings.
A Note on Collection Types and Performance
The Java
Set type is a collection that doesn't allow duplicates. In order to ensure uniqueness when adding an entry to a
Set association Hibernate has to load the entire associations from the database. If you have a large numbers of entries in the association this can be costly in terms of performance.
The same behavior is required for
List types, since Hibernate needs to load the entire association in-order to maintain order. Therefore it is recommended that if you anticipate a large numbers of records in the association that you make the association bidirectional so that the link can be created on the inverse side. For example consider the following code:
def book = new Book(title:"New Grails Book")
def author = Author.get(1)
book.author = author
book.save()
In this example the association link is being created by the child (Book) and hence it is not necessary to manipulate the collection directly resulting in fewer queries and more efficient code. Given an
Author with a large number of associated
Book instances if you were to write code like the following you would see an impact on performance:
def book = new Book(title:"New Grails Book")
def author = Author.get(1)
author.addToBooks(book)
author.save()
A key thing to remember about Grails is that under the surface Grails is using
Hibernate for persistence. If you are coming from a background of using
ActiveRecord or
iBatis Hibernate's "session" model may feel a little strange.
Essentially, Grails automatically binds a Hibernate session to the currently executing request. This allows you to use the
save and
delete methods as well as other GORM methods transparently.
An example of using the
save method can be seen below:
def p = Person.get(1)
p.save()
A major difference with Hibernate is when you call
save it does not necessarily perform any SQL operations
at that point. Hibernate typically batches up SQL statements and executes them at the end. This is typically done for you automatically by Grails, which manages your Hibernate session.
There are occasions, however, when you may want to control when those statements are executed or, in Hibernate terminology, when the session is "flushed". To do so you can use the flush argument to the save method:
def p = Person.get(1)
p.save(flush:true)
Note that in this case all pending SQL statements including previous saves will be synchronized with the db. This also allows you to catch any exceptions thrown, which is typically useful in highly concurrent scenarios involving
optimistic locking:
def p = Person.get(1)
try {
p.save(flush:true)
}
catch(Exception e) {
// deal with exception
}An example of the
delete method can be seen below:
def p = Person.get(1)
p.delete()
By default Grails will use transactional write behind to perform the delete, if you want to perform the delete in place then you can use the
flush argument:
def p = Person.get(1)
p.delete(flush:true)
Using the
flush argument will also allow you to catch any errors that may potentially occur during a delete. A common error that may occur is if you violate a database constraint, although this is normally down to a programming or schema error. The following example shows how to catch a
DataIntegrityViolationException that is thrown when you violate the database constraints:
def p = Person.get(1)try {
p.delete(flush:true)
}
catch(org.springframework.dao.DataIntegrityViolationException e) {
flash.message = "Could not delete person ${p.name}"
redirect(action:"show", id:p.id)
}Note that Grails does not supply a
deleteAll method as deleting data is discouraged and can often be avoided through boolean flags/logic.
If you really need to batch delete data you can use the
executeUpdate method to do batch DML statements:
Customer.executeUpdate("delete Customer c where c.name = :oldName", [oldName:"Fred"])It is critical that you understand how cascading updates and deletes work when using GORM. The key part to remember is the
belongsTo setting which controls which class "owns" a relationship.
Whether it is a one-to-one, one-to-many or many-to-many if you define
belongsTo updates and deletes will cascade from the owning class to its possessions (the other side of the relationship).
If you
do not define
belongsTo then no cascades will happen and you will have to manually save each object.
Here is an example:
class Airport {
String name
static hasMany = [flights:Flight]
}
class Flight {
String number
static belongsTo = [airport:Airport]
}If I now create an
Airport and add some
Flights to it I can save the
Airport and have the updates cascaded down to each flight, hence saving the whole object graph:
new Airport(name:"Gatwick")
.addToFlights(new Flight(number:"BA3430"))
.addToFlights(new Flight(number:"EZ0938"))
.save()
Conversely if I later delete the
Airport all
Flights associated with it will also be deleted:
def airport = Airport.findByName("Gatwick")
airport.delete()However, if I were to remove
belongsTo then the above cascading deletion code
would not work. To understand this better take a look at the summaries below that describe the default behaviour of GORM with regards to specific associations.
Bidirectional one-to-many with belongsTo
class A { static hasMany = [bees:B] }
class B { static belongsTo = [a:A] }In the case of a bidirectional one-to-many where the many side defines a
belongsTo then the cascade strategy is set to "ALL" for the one side and "NONE" for the many side.
Unidirectional one-to-many
class A { static hasMany = [bees:B] }
class B { }In the case of a unidirectional one-to-many where the many side defines no belongsTo then the cascade strategy is set to "SAVE-UPDATE".
Bidirectional one-to-many no belongsTo
class A { static hasMany = [bees:B] }
class B { A a }In the case of a bidirectional one-to-many where the many side does not define a
belongsTo then the cascade strategy is set to "SAVE-UPDATE" for the one side and "NONE" for the many side.
Unidirectional One-to-one with belongsTo
class A { }
class B { static belongsTo = [a:A] }In the case of a unidirectional one-to-one association that defines a
belongsTo then the cascade strategy is set to "ALL" for the owning side of the relationship (A->B) and "NONE" from the side that defines the
belongsTo (B->A)
Note that if you need further control over cascading behaviour, you can use the
ORM DSL.
Associations in GORM are by default lazy. This is best explained by example:
class Airport {
String name
static hasMany = [flights:Flight]
}
class Flight {
String number
static belongsTo = [airport:Airport]
}Given the above domain classes and the following code:
def airport = Airport.findByName("Gatwick")
airport.flights.each {
println it.name
}GORM will execute a single SQL query to fetch the
Airport instance and then 1 extra query
for each iteration over the
flights association. In other words you get N+1 queries.
This can sometimes be optimal depending on the frequency of use of the association as you may have logic that dictates the associations is only accessed on certain occasions.
Configuring Eager Fetching
An alternative is to use eager fetching which can specified as follows:
class Airport {
String name
static hasMany = [flights:Flight]
static mapping = {
flight fetch:"join"
}
}In this case the association will be
Airport instance and the
flights association will be loaded all at once (depending on the mapping). This has the benefit of requiring fewer queries, however should be used carefully as you could load your entire database into memory with too many eager associations.
Associations can also be declared non-lazy using the ORM DSL
Using Batch Fetching
Although eager fetching is appropriate for some cases, it is not always desirable. If you made everything eager you could quite possibly load your entire database into memory resulting in performance and memory problems. An alternative to eager fetching is to use batch fetching. Essentially, you can configure Hibernate to lazily fetch results in "batches". For example:
class Airport {
String name
static hasMany = [flights:Flight]
static mapping = {
flight batchSize:10
}
}In this case, due to the
batchSize argument, when you iterate over the
flights association, Hibernate will fetch results in batches of 10. For example if you had an
Airport that had 30 flights, if you didn't configure batch fetching you would get 1 query to fetch the
Airport and then
30 queries to fetch each flight. With batch fetching you get 1 query to fetch the
Airport and 3 queries to fetch each
Flight in batches of 10. In other words, batch fetching is an optimization of the lazy fetching strategy. Batch fetching can also be configured at the class level as follows:
class Flight {
…
static mapping = {
batchSize 10
}
}Optimistic Locking
By default GORM classes are configured for optimistic locking. Optimistic locking essentially is a feature of Hibernate which involves storing a version number in a special
version column in the database.
The
version column gets read into a
version property that contains the current versioned state of persistent instance which you can access:
def airport = Airport.get(10)println airport.version
When you perform updates Hibernate will automatically check the version property against the version column in the database and if they differ will throw a
StaleObjectException and the transaction will be rolled back.
This is useful as it allows a certain level of atomicity without resorting to pessimistic locking that has an inherit performance penalty. The downside is that you have to deal with this exception if you have highly concurrent writes. This requires flushing the session:
def airport = Airport.get(10)try {
airport.name = "Heathrow"
airport.save(flush:true)
}
catch(org.springframework.dao.OptimisticLockingFailureException e) {
// deal with exception
}The way you deal with the exception depends on the application. You could attempt a programmatic merge of the data or go back to the user and ask them to resolve the conflict.
Alternatively, if it becomes a problem you can resort to pessimistic locking.
Pessimistic Locking
Pessimistic locking is equivalent to doing a SQL "SELECT * FOR UPDATE" statement and locking a row in the database. This has the implication that other read operations will be blocking until the lock is released.
In Grails pessimistic locking is performed on an existing instance via the
lock method:
def airport = Airport.get(10)
airport.lock() // lock for update
airport.name = "Heathrow"
airport.save()
Grails will automatically deal with releasing the lock for you once the transaction has been committed. However, in the above case what we are doing is "upgrading" from a regular SELECT to a SELECT..FOR UPDATE and another thread could still have updated the record in between the call to get() and the call to lock().
To get around this problem you can use the static
lock method that takes an id just like
get:
def airport = Airport.lock(10) // lock for update
airport.name = "Heathrow"
airport.save()
In this case only SELECT..FOR UPDATE is issued.
Though Grails, through Hibernate, supports pessimistic locking, the embedded HSQLDB shipped with Grails which is used as the default in-memory database does not. If you need to test pessimistic locking you will need to do so against a database that does have support such as MySQL.
As well as the
lock method you can also obtain a pessimistic locking using queries. For example using a dynamic finder:
def airport = Airport.findByName("Heathrow", [lock:true])Or using criteria:
def airport = Airport.createCriteria().get {
eq('name', 'Heathrow')
lock true
}GORM supports a number of powerful ways to query from dynamic finders, to criteria to Hibernate's object oriented query language HQL.
Groovy's ability to manipulate collections via
GPath and methods like sort, findAll and so on combined with GORM results in a powerful combination.
However, let's start with the basics.
Listing instances
If you simply need to obtain all the instances of a given class you can use the
list method:
The
list method supports arguments to perform pagination:
def books = Book.list(offset:10, max:20)
as well as sorting:
def books = Book.list(sort:"title", order:"asc")
Here, the
sort argument is the name of the domain class property that you wish to sort on, and the
order argument is either
asc for
ascending or
desc for
descending.
Retrieval by Database Identifier
The second basic form of retrieval is by database identifier using the
get method:
You can also obtain a list of instances for a set of identifiers using
getAll:
def books = Book.getAll(23, 93, 81)
GORM supports the concept of
dynamic finders. A dynamic finder looks like a static method invocation, but the methods themselves don't actually exist in any form at the code level.
Instead, a method is auto-magically generated using code synthesis at runtime, based on the properties of a given class. Take for example the
Book class:
class Book {
String title
Date releaseDate
Author author
}
class Author {
String name
}The
Book class has properties such as
title,
releaseDate and
author. These can be used by the
findBy and
findAllBy methods in the form of "method expressions":
def book = Book.findByTitle("The Stand")book = Book.findByTitleLike("Harry Pot%")book = Book.findByReleaseDateBetween( firstDate, secondDate )book = Book.findByReleaseDateGreaterThan( someDate )book = Book.findByTitleLikeOrReleaseDateLessThan( "%Something%", someDate )Method Expressions
A method expression in GORM is made up of the prefix such as
findBy followed by an expression that combines one or more properties. The basic form is:
Book.findBy([Property][Comparator][Boolean Operator])?[Property][Comparator]
The tokens marked with a '?' are optional. Each comparator changes the nature of the query. For example:
def book = Book.findByTitle("The Stand")book = Book.findByTitleLike("Harry Pot%")In the above example the first query is equivalent to equality whilst the latter, due to the
Like comparator, is equivalent to a SQL
like expression.
The possible comparators include:
InList - In the list of given valuesLessThan - less than the given valueLessThanEquals - less than or equal a give valueGreaterThan - greater than a given valueGreaterThanEquals - greater than or equal a given valueLike - Equivalent to a SQL like expressionIlike - Similar to a Like, except case insensitiveNotEqual - Negates equalityBetween - Between two values (requires two arguments)IsNotNull - Not a null value (doesn't require an argument)IsNull - Is a null value (doesn't require an argument)
Notice that the last 3 require different numbers of method arguments compared to the rest, as demonstrated in the following example:
def now = new Date()
def lastWeek = now - 7
def book = Book.findByReleaseDateBetween( lastWeek, now )books = Book.findAllByReleaseDateIsNull()
books = Book.findAllByReleaseDateIsNotNull()
Boolean logic (AND/OR)
Method expressions can also use a boolean operator to combine two criteria:
def books =
Book.findAllByTitleLikeAndReleaseDateGreaterThan("%Java%", new Date()-30)In this case we're using
And in the middle of the query to make sure both conditions are satisfied, but you could equally use
Or:
def books =
Book.findAllByTitleLikeOrReleaseDateGreaterThan("%Java%", new Date()-30)At the moment, you can only use dynamic finders with a maximum of two criteria, i.e. the method name can only have one boolean operator. If you need to use more, you should consider using either
Criteria or the
HQL.
Querying Associations
Associations can also be used within queries:
def author = Author.findByName("Stephen King")def books = author ? Book.findAllByAuthor(author) : []In this case if the
Author instance is not null we use it in a query to obtain all the
Book instances for the given
Author.
Pagination & Sorting
The same pagination and sorting parameters available on the
list method can also be used with dynamic finders by supplying a map as the final parameter:
def books =
Book.findAllByTitleLike("Harry Pot%", [max:3,
offset:2,
sort:"title",
order:"desc"])Criteria is a type safe, advanced way to query that uses a Groovy builder to construct potentially complex queries. It is a much better alternative to using StringBuffer.
Criteria can be used either via the
createCriteria or
withCriteria methods. The builder uses Hibernate's Criteria API, the nodes on this builder map the static methods found in the
Restrictions class of the Hibernate Criteria API. Example Usage:
def c = Account.createCriteria()
def results = c {
between("balance", 500, 1000)
eq("branch", "London")
or {
like("holderFirstName", "Fred%")
like("holderFirstName", "Barney%")
}
maxResults(10)
order("holderLastName", "desc")
}This criteria will select up to 10
Account objects matching the following criteria:
balance is between 500 and 1000branch is 'London'holderFirstName starts with 'Fred' or 'Barney'
The results will be sorted in descending ordery by
holderLastName.
Conjunctions and Disjunctions
As demonstrated in the previous example you can group criteria in a logical OR using a
or { } block:
or {
between("balance", 500, 1000)
eq("branch", "London")
}This also works with logical AND:
and {
between("balance", 500, 1000)
eq("branch", "London")
}And you can also negate using logical NOT:
not {
between("balance", 500, 1000)
eq("branch", "London")
}All top level conditions are implied to be AND'd together.
Querying Associations
Associations can be queried by having a node that matches the property name. For example say the
Account class had many
Transaction objects:
class Account {
…
def hasMany = [transactions:Transaction]
Set transactions
…
}
We can query this association by using the property name
transaction as a builder node:
def c = Account.createCriteria()
def now = new Date()
def results = c.list {
transactions {
between('date',now-10, now)
}
}
The above code will find all the
Account instances that have performed
transactions within the last 10 days.
You can also nest such association queries within logical blocks:
def c = Account.createCriteria()
def now = new Date()
def results = c.list {
or {
between('created',now-10,now)
transactions {
between('date',now-10, now)
}
}
}
Here we find all accounts that have either performed transactions in the last 10 days OR have been recently created in the last 10 days.
Querying with Projections
Projections may be used to customise the results. To use projections you need to define a "projections" node within the criteria builder tree. There are equivalent methods within the projections node to the methods found in the Hibernate
Projections class:
def c = Account.createCriteria()def numberOfBranches = c.get {
projections {
countDistinct('branch')
}
}Using SQL Restrictions
You can access Hibernate's SQL Restrictions capabilities.
def c = Person.createCriteria()def peopleWithShortFirstNames = c.list {
sqlRestriction "char_length( first_name ) <= 4"
}
Note that the parameter there is SQL. The first_name attribute referenced in the example relates to the persistence model,
not the object model. The Person class may have a property named firstName which is mapped to a column in the database
named first_name.Also note that the SQL used here is not necessarily portable across databases.
Using Scrollable Results
You can use Hibernate's
ScrollableResults feature by calling the scroll method:
def results = crit.scroll {
maxResults(10)
}
def f = results.first()
def l = results.last()
def n = results.next()
def p = results.previous()def future = results.scroll(10)
def accountNumber = results.getLong('number')
To quote the documentation of Hibernate ScrollableResults:
A result iterator that allows moving around within the results by arbitrary increments. The Query / ScrollableResults pattern is very similar to the JDBC PreparedStatement/ ResultSet pattern and the semantics of methods of this interface are similar to the similarly named methods on ResultSet.
Contrary to JDBC, columns of results are numbered from zero.
Setting properties in the Criteria instance
If a node within the builder tree doesn't match a particular criterion it will attempt to set a property on the Criteria object itself. Thus allowing full access to all the properties in this class. The below example calls
setMaxResults and
setFirstResult on the
Criteria instance:
import org.hibernate.FetchMode as FM
…
def results = c.list {
maxResults(10)
firstResult(50)
fetchMode("aRelationship", FM.EAGER)
}Querying with Eager Fetching
In the section on
Eager and Lazy Fetching we discussed how to declaratively specify fetching to avoid the N+1 SELECT problem. However, this can also be achieved using a criteria query:
def criteria = Task.createCriteria()
def tasks = criteria.list{
eq "assignee.id", task.assignee.id
join 'assignee'
join 'project'
order 'priority', 'asc'
}Notice the usage of the
join method. This method indicates the criteria API that a
JOIN query should be used to obtain the results.
Method Reference
If you invoke the builder with no method name such as:
The build defaults to listing all the results and hence the above is equivalent to:
| Method | Description |
|---|
|
| list | This is the default method. It returns all matching rows. |
| get | Returns a unique result set, i.e. just one row. The criteria has to be formed that way, that it only queries one row. This method is not to be confused with a limit to just the first row. |
| scroll | Returns a scrollable result set. |
| listDistinct | If subqueries or associations are used, one may end up with the same row multiple times in the result set, this allows listing only distinct entities and is equivalent to DISTINCT_ROOT_ENTITY of the CriteriaSpecification class. |
| count | Returns the number of matching rows. |
GORM classes also support Hibernate's query language HQL, a very complete reference for which can be found
Chapter 14. HQL: The Hibernate Query Language of the Hibernate documentation.
GORM provides a number of methods that work with HQL including
find,
findAll and
executeQuery. An example of a query can be seen below:
def results =
Book.findAll("from Book as b where b.title like 'Lord of the%'")Positional and Named Parameters
In this case the value passed to the query is hard coded, however you can equally use positional parameters:
def results =
Book.findAll("from Book as b where b.title like ?", ["The Shi%"])def author = Author.findByName("Stephen King")
def books = Book.findAll("from Book as book where book.author = ?", [author])Or even named parameters:
def results =
Book.findAll("from Book as b where b.title like :search or b.author like :search",
[search:"The Shi%"])def author = Author.findByName("Stephen King")
def books = Book.findAll("from Book as book where book.author = :author",
[author: author])Multiline Queries
If you need to separate the query across multiple lines you can use a line continuation character:
def results = Book.findAll("\
from Book as b, \
Author as a \
where b.author = a and a.surname = ?", ['Smith'])
Groovy multiline strings will NOT work with HQL queries
Pagination and Sorting
You can also perform pagination and sorting whilst using HQL queries. To do so simply specify the pagination options as a map at the end of the method call and include an "ORDER BY" clause in the HQL:
def results =
Book.findAll("from Book as b where b.title like 'Lord of the%' order by b.title asc",
[max:10, offset:20])The following sections cover more advanced usages of GORM including caching, custom mapping and events.
GORM supports the registration of events as methods that get fired when certain events occurs such as deletes, inserts and updates. The following is a list of supported events:
beforeInsert - Executed before an object is initially persisted to the databsebeforeUpdate - Executed before an object is updatedbeforeDelete - Executed before an object is deletedafterInsert - Executed after an object is persisted to the databaseafterUpdate - Executed after an object has been updatedafterDelete - Executed after an object has been updatedonLoad - Executed when an object is loaded from the database
To add an event simply register the relevant closure with your domain class.
Do not attempt to flush the session within an event (such as with obj.save(flush:true)). Since events are fired during flushing this will cause a StackOverflowError.
Event types
The beforeInsert event
Fired before an object is saved to the db
class Person {
Date dateCreated def beforeInsert() {
dateCreated = new Date()
}
}The beforeUpdate event
Fired before an existing object is updated
class Person {
Date dateCreated
Date lastUpdated def beforeInsert() {
dateCreated = new Date()
}
def beforeUpdate() {
lastUpdated = new Date()
}
}The beforeDelete event
Fired before an object is deleted.
class Person {
String name
Date dateCreated
Date lastUpdated def beforeDelete() {
ActivityTrace.withNewSession {
new ActivityTrace(eventName:"Person Deleted",data:name).save()
}
}
}Notice the usage of
withNewSession method above. Since events are triggered whilst Hibernate is flushing using persistence methods like
save() and
delete() won't result in objects being saved unless you run your operations with a new
Session.
Fortunately the
withNewSession method allows you to share the same transactional JDBC connection even though you're using a different underlying
Session.
The onLoad event
Fired when an object is loaded from the db:
class Person {
String name
Date dateCreated
Date lastUpdated def onLoad() {
name = "I'm loaded"
}
}Automatic timestamping
The examples above demonstrated using events to update a
lastUpdated and
dateCreated property to keep track of updates to objects. However, this is actually not necessary. By merely defining a
lastUpdated and
dateCreated property these will be automatically updated for you by GORM.
If this is not the behaviour you want you can disable this feature with:
class Person {
Date dateCreated
Date lastUpdated
static mapping = {
autoTimestamp false
}
}Grails domain classes can be mapped onto many legacy schemas via an Object Relational Mapping Domain Specify Language. The following sections takes you through what is possible with the ORM DSL.
None if this is necessary if you are happy to stick to the conventions defined by GORM for table, column names and so on. You only needs this functionality if you need to in anyway tailor the way GORM maps onto legacy schemas or performs caching
Custom mappings are defined using a a static
mapping block defined within your domain class:
class Person {
..
static mapping = { }
}Table names
The database table name which the class maps to can be customized using a call to
table:
class Person {
..
static mapping = {
table 'people'
}
}In this case the class would be mapped to a table called
people instead of the default name of
person.
Column names
It is also possible to customize the mapping for individual columns onto the database. For example if its the name you want to change you can do:
class Person {
String firstName
static mapping = {
table 'people'
firstName column:'First_Name'
}
}In this case we define method calls that match each property name (in this case
firstName). We then use the named parameter
column, to specify the column name to map onto.
Column type
GORM supports configuration of Hibernate types via the DSL using the type attribute. This includes specifing user types that subclass the Hibernate
org.hibernate.usertype.UserType class, which allows complete customization of how a type is persisted. As an example
if you had a
PostCodeType you could use it as follows:
class Address {
String number
String postCode
static mapping = {
postCode type:PostCodeType
}
}Alternatively if you just wanted to map it to one of Hibernate's basic types other than the default chosen by Grails you could use:
class Address {
String number
String postCode
static mapping = {
postCode type:'text'
}
}This would make the
postCode column map to the SQL TEXT or CLOB type depending on which database is being used.
See the Hibernate documentation regarding
Basic Types for further information.
One-to-One Mapping
In the case of associations it is also possible to change the foreign keys used to map associations. In the case of a one-to-one association this is exactly the same as any regular column. For example consider the below:
class Person {
String firstName
Address address
static mapping = {
table 'people'
firstName column:'First_Name'
address column:'Person_Adress_Id'
}
}By default the
address association would map to a foreign key column called
address_id. By using the above mapping we have changed the name of the foreign key column to
Person_Adress_Id.
One-to-Many Mapping
With a bidirectional one-to-many you can change the foreign key column used simple by changing the column name on the many side of the association as per the example in the previous section on one-to-one associations. However, with unidirectional association the foreign key needs to be specified on the association itself. For example given a unidirectional one-to-many relationship between
Person and
Address the following code will change the foreign key in the
address table:
class Person {
String firstName
static hasMany = [addresses:Address]
static mapping = {
table 'people'
firstName column:'First_Name'
addresses column:'Person_Address_Id'
}
}If you don't want the column to be in the
address table, but instead some intermediate join table you can use the
joinTable parameter:
class Person {
String firstName
static hasMany = [addresses:Address]
static mapping = {
table 'people'
firstName column:'First_Name'
addresses joinTable:[name:'Person_Addresses', key:'Person_Id', column:'Address_Id']
}
}Many-to-Many Mapping
Grails, by default maps a many-to-many association using a join table. For example consider the below many-to-many association:
class Group {
…
static hasMany = [people:Person]
}
class Person {
…
static belongsTo = Group
static hasMany = [groups:Group]
}In this case Grails will create a join table called
group_person containing foreign keys called
person_id and
group_id referencing the
person and
group tables. If you need to change the column names you can specify a column within the mappings for each class.
class Group {
…
static mapping = {
people column:'Group_Person_Id'
}
}
class Person {
…
static mapping = {
groups column:'Group_Group_Id'
}
}You can also specify the name of the join table to use:
class Group {
…
static mapping = {
people column:'Group_Person_Id',joinTable:'PERSON_GROUP_ASSOCIATIONS'
}
}
class Person {
…
static mapping = {
groups column:'Group_Group_Id',joinTable:'PERSON_GROUP_ASSOCIATIONS'
}
}Setting up caching
Hibernate features a second-level cache with a customizable cache provider. This needs to be configured in the
grails-app/conf/DataSource.groovy file as follows:
hibernate {
cache.use_second_level_cache=true
cache.use_query_cache=true
cache.provider_class='org.hibernate.cache.EhCacheProvider'
}You can of course customize these settings how you desire, for example if you want to use a distributed caching mechanism.
For further reading on caching and in particular Hibernate's second-level cache, refer to the Hibernate documentation on the subject.
Caching instances
In your mapping block to enable caching with the default settings use a call to the
cache method:
class Person {
..
static mapping = {
table 'people'
cache true
}
}This will configure a 'read-write' cache that includes both lazy and non-lazy properties. If you need to customize this further you can do:
class Person {
..
static mapping = {
table 'people'
cache usage:'read-only', include:'non-lazy'
}
}Caching associations
As well as the ability to use Hibernate's second level cache to cache instances you can also cache collections (associations) of objects. For example:
class Person {
String firstName
static hasMany = [addresses:Address]
static mapping = {
table 'people'
version false
addresses column:'Address', cache:true
}
}
class Address {
String number
String postCode
}This will enable a 'read-write' caching mechanism on the addresses collection. You can also use:
cache:'read-write' // or 'read-only' or 'transactional'
To further configure the cache usage.
Caching Queries
You can cache queries such as dynamic finders and criteria. To do so using a dynamic finder you can pass the
cache argument:
def person = Person.findByFirstName("Fred", [cache:true])
Note that in order for the results of the query to be cached, you still need to enable caching in your mapping as discussed in the previous section.
You can also cache criteria queries:
def people = Person.withCriteria {
like('firstName', 'Fr%')
cache true
}Cache usages
Below is a description of the different cache settings and their usages:
read-only - If your application needs to read but never modify instances of a persistent class, a read-only cache may be used.read-write - If the application needs to update data, a read-write cache might be appropriate.nonstrict-read-write - If the application only occasionally needs to update data (ie. if it is extremely unlikely that two transactions would try to update the same item simultaneously) and strict transaction isolation is not required, a nonstrict-read-write cache might be appropriate.transactional - The transactional cache strategy provides support for fully transactional cache providers such as JBoss TreeCache. Such a cache may only be used in a JTA environment and you must specify hibernate.transaction.manager_lookup_class in the grails-app/conf/DataSource.groovy file's hibernate config.
By default GORM classes uses
table-per-hierarchy inheritance mapping. This has the disadvantage that columns cannot have a
NOT-NULL constraint applied to them at the db level. If you would prefer to use a
table-per-subclass inheritance strategy you can do so as follows:
class Payment {
Long id
Long version
Integer amount static mapping = {
tablePerHierarchy false
}
}
class CreditCardPayment extends Payment {
String cardNumber
}The mapping of the root
Payment class specifies that it will not be using
table-per-hierarchy mapping for all child classes.
You can customize how GORM generates identifiers for the database using the DSL. By default GORM relies on the native database mechanism for generating ids. This is by far the best approach, but there are still many schemas that have different approaches to identity.
To deal with this Hibernate defines the concept of an id generator. You can customize the id generator and the column it maps to as follows:
class Person {
..
static mapping = {
table 'people'
version false
id generator:'hilo', params:[table:'hi_value',column:'next_value',max_lo:100]
}
}In this case we're using one of Hibernate's built in 'hilo' generators that uses a separate table to generate ids.
For more information on the different Hibernate generators refer to the Hibernate reference documentation
Note that if you want to merely customise the column that the id lives on you can do:
class Person {
..
static mapping = {
table 'people'
version false
id column:'person_id'
}
}GORM supports the concept of composite identifiers (identifiers composed from 2 or more properties). It is not an approach we recommend, but is available to you if you need it:
class Person {
String firstName
String lastName static mapping = {
id composite:['firstName', 'lastName']
}
}The above will create a composite id of the
firstName and
lastName properties of the Person class. When you later need to retrieve an instance by id you have to use a prototype of the object itself:
def p = Person.get(new Person(firstName:"Fred", lastName:"Flintstone"))
println p.firstName
To get the best performance out of your queries it is often necessary to tailor the table index definitions. How you tailor them is domain specific and a matter of monitoring usage patterns of your queries. With GORM's DSL you can specify which columns need to live in which indexes:
class Person {
String firstName
String address
static mapping = {
table 'people'
version false
id column:'person_id'
firstName column:'First_Name', index:'Name_Idx'
address column:'Address', index:'Name_Idx, Address_Index'
}
}As discussed in the section on
Optimistic and Pessimistic Locking, by default GORM uses optimistic locking and automatically injects a
version property into every class which is in turn mapped to a
version column at the database level.
If you're mapping to a legacy schema this can be problematic, so you can disable this feature by doing the following:
class Person {
..
static mapping = {
table 'people'
version false
}
}
If you disable optimistic locking you are essentially on your own with regards to concurrent updates and are open to the risk of users losing (due to data overriding) data unless you use pessimistic locking
Lazy Collections
As discussed in the section on
Eager and Lazy fetching, by default GORM collections use lazy fetching and is is configurable through the
fetchMode setting. However, if you prefer to group all your mappings together inside the
mappings block you can also use the ORM DSL to configure fetching:
class Person {
String firstName
static hasMany = [addresses:Address]
static mapping = {
addresses lazy:false
}
}
class Address {
String street
String postCode
}Lazy Single-Ended Associations
In GORM, one-to-one and many-to-one associations are by default lazy. Non-lazy single ended associations can be problematic in cases when you are loading many entities which have an association to another entity as a new SELECT statement is executed for each loaded entity.
You can make one-to-one and many-to-one associations non-lazy using the same technique as for lazy collections:
class Person {
String firstName
static belongsTo = [address:Address]
static mapping = {
address lazy:false
}
}
class Address {
String street
String postCode
}Here we set the
address property of the
Person class will be eagerly fetched.
Lazy Single-Ended Associations and Proxies
In order to facilitate single-ended lazy associations Hibernate uses runtime generated proxies. The way this works is that Hibernate dynamically subclasses the proxied entity to create the proxy.
In the previous example Hibernate would create a subclass of
Address and return that as a proxy to the real entity. When you call any of the getters or setters Hibernate will initialize the the entity from the database.
Unfortunately this technique can produce surprising results. Consider the following example classes:
class Animal {}
class Mammal extends Animal {}
class Dog extends Mammal {
String name
}
class Owner {
Animal pet
}Given you have an
Owner with a
pet association that is a
Dog consider the following code:
def owner = Owner.get(1)
def pet = Animal.get(owner.petId)
if(pet instanceof Dog) {
// doesn't work!
}Now you may think this code will work, but in fact it will not. The reason is Hibernate creates a dynamic proxy by subclassing
Animal for the
owner.pet association and caches it in the first level cache. So even if the actual proxied class is a
Dog it won't be an instance of the
Dog class due to the way proxies work.
The get around this problem GORM provides an
instanceOf method that should always be used:
def owner = Owner.get(1)
def pet = Animal.get(owner.petId)
if(pet?.instanceof( Dog )) {
// this works
}However, there are cases where this particular Hibernate abstraction may still leak through. For example:
def owner = Owner.get(1)
Dog pet = Animal.get(owner.petId)
In this case you will get a
ClassCastException because the proxied
Animal is not a
Dog even though the actual instance
is a
Dog.
Our best advice is to be aware of Hibernate proxies and how to deal with them when you do run into issues.
As describes in the section on
cascading updates, the primary mechanism to control the way updates and deletes are cascading from one association to another is the
belongsTo static property.
However, the ORM DSL gives you complete access to Hibernate's
transitive persistence capabilities via the
cascade attribute.
Valid settings for the cascade attribute include:
- create - cascades creation of new records from one association to another
- merge - merges the state of a detached association
- save-update - cascades only saves and updates to an association
- delete - cascades only deletes to an association
- lock - useful if a pessimistic lock should be cascaded to its associations
- refresh - cascades refreshes to an association
- evict - cascades evictions (equivalent to discard() in GORM) to associations if set
- all - cascade ALL operations to associations
- all-delete-orphan - Applies only to one-to-many associations and indicates that when a child is removed from an association then it should be automatically deleted. Children are also deleted when the parent is.
It is advisable to read the section in the Hibernate documentation on transitive persistence to obtain a better understanding of the different cascade styles and recommendation for their usage
To specific the cascade attribute simply define one or many (comma-separated) of the aforementioned settings as its value:
class Person {
String firstName
static hasMany = [addresses:Address]
static mapping = {
addresses cascade:"all-delete-orphan"
}
}
class Address {
String street
String postCode
}You saw in an earlier section that you can use composition (via the
embedded property) to break a table into multiple objects. You can achieve a similar effect via Hibernate's custom user types. These are not domain classes themselves, but plain Java or Groovy classes with associated. Each of these types also has a corresponding "meta-type" class that implements
org.hibernate.usertype.UserType.
The
Hibernate reference manual has some information on custom types, but here we will focus on how to map them in Grails. Let's start by taking a look at a simple domain class that uses an old-fashioned (pre-Java 1.5) type-safe enum class:
class Book {
String title
String author
Rating rating static mapping = {
rating type: RatingUserType
}
}All we have done is declare the
rating field the enum type and set the property's type in the custom mapping to the corresponding
UserType implementation. That's all you have to do to start using your custom type. If you want, you can also use the other column settings such as "column" to change the column name and "index" to add it to an index.
Custom types aren't limited to just a single column - they can be mapped to as many columns as you want. In such cases you need to explicitly define in the mapping what columns to use, since Hibernate can only use the property name for a single column. Fortunately, Grails allows you to map multiple columns to a property using this syntax:
class Book {
String title
Name author
Rating rating static mapping = {
name type: NameUserType, {
column name: "first_name"
column name: "last_name"
}
rating type: RatingUserType
}
}The above example will create "first_name" and "last_name" columns for the
author property. You'll be pleased to know that you can also use some of the normal column/property mapping attributes in the column definitions. For example:
column name: "first_name", index: "my_idx", unique: true
The column definitions do
not support the following attributes:
type,
cascade,
lazy,
cache, and
joinTable.
One thing to bear in mind with custom types is that they define the
SQL types for the corresponding database columns. That helps take the burden of configuring them yourself, but what happens if you have a legacy database that uses a different SQL type for one of the columns? In that case, you need to override column's SQL type using the
sqlType attribute:
class Book {
String title
Name author
Rating rating static mapping = {
name type: NameUserType, {
column name: "first_name", sqlType: "text"
column name: "last_name", sqlType: "text"
}
rating type: RatingUserType, sqlType: "text"
}
}Mind you, the SQL type you specify needs to still work with the custom type. So overriding a default of "varchar" with "text" is fine, but overriding "text" with "yes_no" isn't going to work.
You can sort objects using queries arguments such as those found in the
list method:
def airports = Airport.list(sort:'name')
However, you can also declare the sort order declaratively:
class Airport {
…
static mapping = {
sort "name"
}
}You can also configure the sort order if necessary:
class Airport {
…
static mapping = {
sort name:"desc"
}
}Alternatively, you can configure sort order at the association level:
class Airport {
…
static hasMany = [flights:Flight]
static mapping = {
flights sort:'number'
}
}Grails is built on Spring and hence uses Spring's Transaction abstraction for dealing with programmatic transactions. However, GORM classes have been enhanced to make this more trivial through the
withTransaction method which accepts a block the first argument to which is the Spring
TransactionStatus object.
A typical usage scenario is as follows:
def transferFunds = {
Account.withTransaction { status ->
def source = Account.get(params.from)
def dest = Account.get(params.to) def amount = params.amount.toInteger()
if(source.active) {
source.balance -= amount
if(dest.active) {
dest.amount += amount
}
else {
status.setRollbackOnly()
}
}
}}In this example we rollback the transactions if the destination account is not active and if any exception are thrown during the process the transaction will automatically be rolled back.
You can also use "save points" to rollback a transaction to a particular point in time if you don't want to rollback the entire transaction. This can be achieved through the use of Spring's
SavePointManager interface.
The
withTransaction method deals with the begin/commit/rollback logic for you within the scope of the block.
Although constraints are covered in the
Validation section, it is important to mention them here as some of the constraints can affect the way in which the database schema is generated.
Where feasible, Grails uses a domain class's constraints to influence the database columns generated for the corresponding domain class properties.
Consider the following example. Suppose we have a domain model with the following property.
String name
String description
By default, in MySQL, Grails would define these columns as...
column name | data type
description | varchar(255)
But perhaps the business rules for this domain class state that a description can be up to 1000 characters in length. If that were the case, we'd likely define the column as follows
if we were creating the table via an SQL script.
column name | data type
description | TEXT
Chances are we'd also want to have some application-based validation to make sure we don't exceed that 1000 character limit
before we persist any records. In Grails, we achieve this validation via
constraints. We'd add the following constraint declaration to the domain class.
static constraints = {
description(maxSize:1000)
}This constraint would provide both the application-based validation we want and it would also cause the schema to be generated as shown above. Below is a description of the other constraints that influence schema generation.
Constraints Affecting String Properties
If either the
maxSize or the
size constraint is defined, Grails sets the maximum column length based on the constraint value.
In general, it's not advisable to use both constraints on the same domain class property. However, if both the
maxSize constraint and the
size constraint are defined, then Grails sets the column length to the minimum of the
maxSize constraint and the upper bound of the size constraint. (Grails uses the minimum of the two, because any length that exceeds that minimum will result in a validation error.)
If the inList constraint is defined (and the
maxSize and the
size constraints are not defined), then Grails sets the maximum column length based on the length of the longest string in the list of valid values. For example, given a list including values "Java", "Groovy", and "C++", Grails would set the column length to 6 (i.e., the number of characters in the string "Groovy").
Constraints Affecting Numeric Properties
If the
max constraint, the
min constraint, or the
range constraint is defined, Grails attempts to set the column
precision based on the constraint value. (The success of this attempted influence is largely dependent on how Hibernate interacts with the underlying DBMS.)
In general, it's not advisable to combine the pair min/max and range constraints together on the same domain class property. However, if both of these constraints is defined, then Grails uses the minimum precision value from the constraints. (Grails uses the minimum of the two, because any length that exceeds that minimum precision will result in a validation error.)
If the scale constraint is defined, then Grails attempts to set the column
scale based on the constraint value. This rule only applies to floating point numbers (i.e., java.lang.Float, java.Lang.Double, java.lang.BigDecimal, or subclasses of java.lang.BigDecimal). (The success of this attempted influence is largely dependent on how Hibernate interacts with the underlying DBMS.)
The constraints define the minimum/maximum numeric values, and Grails derives the maximum number of digits for use in the precision. Keep in mind that specifying only one of min/max constraints will not affect schema generation (since there could be large negative value of property with max:100, for example), unless specified constraint value requires more digits than default Hibernate column precision is (19 at the moment). For example...
someFloatValue(max:1000000, scale:3)
would yield:
someFloatValue DECIMAL(19, 3) // precision is default
but
someFloatValue(max:12345678901234567890, scale:5)
would yield:
someFloatValue DECIMAL(25, 5) // precision = digits in max + scale
and
someFloatValue(max:100, min:-100000)
would yield:
someFloatValue DECIMAL(8, 2) // precision = digits in min + default scale
A controller handles requests and creates or prepares the response and is request-scoped. In other words a new instance is created for each
request. A controller can generate the response or delegate to a view. To create a controller simply create a class whose name ends with
Controller and place it within the
grails-app/controllers directory.
The default
URL Mapping setup ensures that the first part of your controller name is mapped to a URI and each action defined within your controller maps to URI within the controller name URI.
Creating a controller
Controllers can be created with the
create-controller target. For example try running the following command from the root of a Grails project:
grails create-controller book
The command will result in the creation of a controller at the location
grails-app/controllers/BookController.groovy:
class BookController { … }BookController by default maps to the /book URI (relative to your application root).
The create-controller command is merely for convenience and you can just as easily create controllers using your favorite text editor or IDE
Creating Actions
A controller can have multiple properties that are each assigned a block of code. Each of these properties maps to a URI:
class BookController {
def list = { // do controller logic
// create model return model
}
}This example maps to the
/book/list URI by default thanks to the property being named
list.
The Default Action
A controller has the concept of a default URI that maps to the root URI of the controller. By default the default URI in this case is
/book. The default URI is dictated by the following rules:
- If only one action is present the default URI for a controller maps to that action.
- If you define an
index action which is the action that handles requests when no action is specified in the URI /book
- Alternatively you can set it explicitly with the
defaultAction property:
def defaultAction = "list"
Available Scopes
Scopes are essentially hash like objects that allow you to store variables. The following scopes are available to controllers:
- servletContext - Also known as application scope, this scope allows you to share state across the entire web application. The servletContext is an instance of javax.servlet.ServletContext
- session - The session allows associating state with a given user and typically uses cookies to associate a session with a client. The session object is an instance of HttpSession
- request - The request object allows the storage of objects for the current request only. The request object is an instance of HttpServletRequest
- params - Mutable map of incoming request (CGI) parameters
- flash - See below.
Accessing Scopes
Scopes can be accessed using the variable names above in combination with Groovy's array index operator even on classes provided by the Servlet API such as the
HttpServletRequest:
class BookController {
def find = {
def findBy = params["findBy"]
def appContext = request["foo"]
def loggedUser = session["logged_user"] }
}You can even access values within scopes using the de-reference operator making the syntax even clearer:
class BookController {
def find = {
def findBy = params.findBy
def appContext = request.foo
def loggedUser = session.logged_user }
}This is one of the ways that Grails unifies access to the different scopes.
Using Flash Scope
Grails supports the concept of
flash scope is a temporary store for attributes which need to be available for this request and the next request only. Afterwards the attributes are cleared. This is useful for setting a message directly before redirection, for example:
def delete = {
def b = Book.get( params.id )
if(!b) {
flash.message = "User not found for id ${params.id}"
redirect(action:list)
}
… // remaining code
}Returning the Model
A model is essentially a map that the view uses when rendering. The keys within that map translate to variable names accessible by the view. There are a couple of ways to return a model, the first way is to explicitly return a map instance:
def show = {
[ book : Book.get( params.id ) ]
}If no explicit model is returned the controller's properties will be used as the model thus allowing you to write code like this:
class BookController {
List books
List authors
def list = {
books = Book.list()
authors = Author.list()
}
}
This is possible due to the fact that controllers are prototype scoped. In other words a new controller is created for each request. Otherwise code such as the above would not be thread safe.
In the above example the
books and
authors properties will be available in the view.
A more advanced approach is to return an instance of the Spring
ModelAndView class:
import org.springframework.web.servlet.ModelAndViewdef index = {
def favoriteBooks = … // get some books just for the index page, perhaps your favorites // forward to the list view to show them
return new ModelAndView("/book/list", [ bookList : favoriteBooks ])
}Selecting the View
In both of the previous two examples there was no code that specified which
view to render. So how does Grails know which view to pick? The answer lies in the conventions. For the action:
class BookController {
def show = {
[ book : Book.get( params.id ) ]
}
}Grails will automatically look for a view at the location
grails-app/views/book/show.gsp (actually Grails will try to look for a JSP first, as Grails can equally be used with JSP).
If you wish to render another view, then the
render method there to help:
def show = {
def map = [ book : Book.get( params.id ) ]
render(view:"display", model:map)
}In this case Grails will attempt to render a view at the location
grails-app/views/book/display.gsp. Notice that Grails automatically qualifies the view location with the
book folder of the
grails-app/views directory. This is convenient, but if you have some shared views you need to access instead use:
def show = {
def map = [ book : Book.get( params.id ) ]
render(view:"/shared/display", model:map)
}In this case Grails will attempt to render a view at the location
grails-app/views/shared/display.gsp.
Rendering a Response
Sometimes its easier (typically with Ajax applications) to render snippets of text or code to the response directly from the controller. For this, the highly flexible
render method can be used:
The above code writes the text "Hello World!" to the response, other examples include:
// write some markup
render {
for(b in books) {
div(id:b.id, b.title)
}
}
// render a specific view
render(view:'show')
// render a template for each item in a collection
render(template:'book_template', collection:Book.list())
// render some text with encoding and content type
render(text:"<xml>some xml</xml>",contentType:"text/xml",encoding:"UTF-8")If you plan on using Groovy's MarkupBuilder to generate html for use with the render method becareful of naming clashes between html elements and Grails tags. e.g.
def login = {
StringWriter w = new StringWriter()
def builder = new groovy.xml.MarkupBuilder(w)
builder.html{
head{
title 'Log in'
}
body{
h1 'Hello'
form{ }
}
} def html = w.toString()
render html
}Will actually
call the form tag (which will return some text that will be ignored by the MarkupBuilder). To correctly output a <form> elemement, use the following:
def login = {
// …
body{
h1 'Hello'
builder.form{ }
}
// …
}Redirects
Actions can be redirected using the
redirect method present in all controllers:
class OverviewController {
def login = {} def find = {
if(!session.user)
redirect(action:login)
…
}
} Internally the
redirect method uses the
HttpServletResonse object's
sendRedirect method.
The
redirect method expects either:
- Another closure within the same controller class:
// Call the login action within the same class
redirect(action:login)
- The name of a controller and action:
// Also redirects to the index action in the home controller
redirect(controller:'home',action:'index')
- A URI for a resource relative the application context path:
// Redirect to an explicit URI
redirect(uri:"/login.html")// Redirect to a URL
redirect(url:"http://grails.org") Parameters can be optionally passed from one action to the next using the
params argument of the method:
redirect(action:myaction, params:[myparam:"myvalue"])
These parameters are made available through the
params dynamic property that also accesses request parameters. If a parameter is specified with the same name as a request parameter the request parameter is overridden and the controller parameter used.
Since the
params object is also a map, you can use it to pass the current request parameters from one action to the next:
redirect(action:"next", params:params)
Finally, you can also include a fragment in the target URI:
redirect(controller: "test", action: "show", fragment: "profile")
will (depending on the URL mappings) redirect to something like "/myapp/test/show#profile".
h4. Chaining
Actions can also be chained. Chaining allows the model to be retained from one action to the next. For example calling the
first action in the below action:
class ExampleChainController {
def first = {
chain(action:second,model:[one:1])
}
def second = {
chain(action:third,model:[two:2])
}
def third = {
[three:3])
}
}
Results in the model:
The model can be accessed in subsequent controller actions in the chain via the
chainModel map. This dynamic property only exists in actions following the call to the
chain method:
class ChainController { def nextInChain = {
def model = chainModel.myModel
…
}
}
Like the
redirect method you can also pass parameters to the
chain method:
chain(action:"action1", model:[one:1], params:[myparam:"param1"])
Often it is useful to intercept processing based on either request, session or application state. This can be achieved via action interceptors. There are currently 2 types of interceptors: before and after.
If your interceptor is likely to apply to more than one controller, you are almost certainly better off writing a Filter. Filters can be applied to multiple controllers or URIs, without the need to change the logic of each controller
Before Interception
The
beforeInterceptor intercepts processing before the action is executed. If it returns
false then the intercepted action will not be executed. The interceptor can be defined for all actions in a controller as follows:
def beforeInterceptor = {
println "Tracing action ${actionUri}"
}
The above is declared inside the body of the controller definition. It will be executed before all actions and does not interfere with processing. A common use case is however for authentication:
def beforeInterceptor = [action:this.&auth,except:'login']
// defined as a regular method so its private
def auth() {
if(!session.user) {
redirect(action:'login')
return false
}
}
def login = {
// display login page
}
The above code defines a method called
auth. A method is used so that it is not exposed as an action to the outside world (i.e. it is private). The
beforeInterceptor then defines an interceptor that is used on all actions 'except' the login action and is told to execute the 'auth' method. The 'auth' method is referenced using Groovy's method pointer syntax, within the method itself it detects whether there is a user in the session otherwise it redirects to the login action and returns false, instruction the intercepted action not to be processed.
After Interception
To define an interceptor that is executed after an action use the
afterInterceptor property:
def afterInterceptor = { model ->
println "Tracing action ${actionUri}"
}The after interceptor takes the resulting model as an argument and can hence perform post manipulation of the model or response.
An after interceptor may also modify the Spring MVC
ModelAndView object prior to rendering. In this case, the above example becomes:
def afterInterceptor = { model, modelAndView ->
println "Current view is ${modelAndView.viewName}"
if(model.someVar) modelAndView.viewName = "/mycontroller/someotherview"
println "View is now ${modelAndView.viewName}"
}This allows the view to be changed based on the model returned by the current action. Note that the
modelAndView may be
null if the action being intercepted called redirect or render.
Interception Conditions
Rails users will be familiar with the authentication example and how the 'except' condition was used when executing the interceptor (interceptors are called 'filters' in Rails, this terminology conflicts with the servlet filter terminology in Java land):
def beforeInterceptor = [action:this.&auth,except:'login']
This executes the interceptor for all actions except the specified action. A list of actions can also be defined as follows:
def beforeInterceptor = [action:this.&auth,except:['login','register']]
The other supported condition is 'only', this executes the interceptor for only the specified actions:
def beforeInterceptor = [action:this.&auth,only:['secure']]
Data binding is the act of "binding" incoming request parameters onto the properties of an object or an entire graph of objects. Data binding should deal with all necessary type conversion since request parameters, which are typically delivered via a form submission, are always strings whilst the properties of a Groovy or Java object may well not be.
Grails uses
Spring's underlying data binding capability to perform data binding.
Binding Request Data to the Model
There are two ways to bind request parameters onto the properties of a domain class. The first involves using a domain classes' implicit constructor:
def save = {
def b = new Book(params)
b.save()
}The data binding happens within the code
new Book(params). By passing the
params object to the domain class constructor Grails automatically recognizes that you are trying to bind from request parameters. So if we had an incoming request like:
/book/save?title=The%20Stand&author=Stephen%20King
Then the
title and
author request parameters would automatically get set on the domain class. If you need to perform data binding onto an existing instance then you can use the
properties property:
def save = {
def b = Book.get(params.id)
b.properties = params
b.save()
}This has exactly the same effect as using the implicit constructor.
Data binding and Single-ended Associations
If you have a
one-to-one or
many-to-one association you can use Grails' data binding capability to update these relationships too. For example if you have an incoming request such as:
Grails will automatically detect the
.id suffix on the request parameter and look-up the
Author instance for the given id when doing data binding such as:
Data Binding and Many-ended Associations
If you have a one-to-many or many-to-many association there are different techniques for data binding depending of the association type.
If you have a
Set based association (default for a
hasMany) then the simplest way to populate an association is to simply send a list of identifiers. For example consider the usage of
<g:select> below:
<g:select name="books"
from="${Book.list()}"
size="5" multiple="yes" optionKey="id"
value="${author?.books}" />This produces a select box that allows you to select multiple values. In this case if you submit the form Grails will automatically use the identifiers from the select box to populate the
books association.
However, if you have a scenario where you want to update the properties of the associated objects the this technique won't work. Instead you have to use the subscript operator:
<g:textField name="books[0].title" value="the Stand" />
<g:textField name="books[1].title" value="the Shining" />
However, with
Set based association it is critical that you render the mark-up in the same order that you plan to do the update in. This is because a
Set has no concept of order, so although we're referring to
books0 and
books1 it is not guaranteed that the order of the association will be correct on the server side unless you apply some explicit sorting yourself.
This is not a problem if you use
List based associations, since a
List has a defined order and an index you can refer to. This is also true of
Map based associations.
Note also that if the association you are binding to has a size of 2 and you refer to an element that is outside the size of association:
<g:textField name="books[0].title" value="the Stand" />
<g:textField name="books[1].title" value="the Shining" />
<g:textField name="books[2].title" value="Red Madder" />
Then Grails will automatically create a new instance for you at the defined position. If you "skipped" a few elements in the middle:
<g:textField name="books[0].title" value="the Stand" />
<g:textField name="books[1].title" value="the Shining" />
<g:textField name="books[5].title" value="Red Madder" />
Then Grails will automatically create instances in between. For example in the above case Grails will create 4 additional instances if the association being bound had a size of 2.
Data binding with Multiple domain classes
It is possible to bind data to multiple domain objects from the
params object.
For example so you have an incoming request to:
/book/save?book.title=The%20Stand&author.name=Stephen%20King
You'll notice the difference with the above request is that each parameter has a prefix such as
author. or
book. which is used to isolate which parameters belong to which type. Grails'
params object is like a multi-dimensional hash and you can index into to isolate only a subset of the parameters to bind.
def b = new Book(params['book'])
Notice how we use the prefix before the first dot of the
book.title parameter to isolate only parameters below this level to bind. We could do the same with an
Author domain class:
def a = new Author(params['author'])
Data binding and type conversion errors
Sometimes when performing data binding it is not possible to convert a particular String into a particular target type. What you get is a type conversion error. Grails will retain type conversion errors inside the
errors property of a Grails domain class. Take this example:
class Book {
…
URL publisherURL
}Here we have a domain class
Book that uses the Java concrete type
java.net.URL to represent URLs. Now say we had an incoming request such as:
/book/save?publisherURL=a-bad-url
In this case it is not possible to bind the string
a-bad-url to the
publisherURL property os a type mismatch error occurs. You can check for these like this:
def b = new Book(params)if(b.hasErrors()) {
println "The value ${b.errors.getFieldError('publisherURL').rejectedValue} is not a valid URL!"
}Although we have not yet covered error codes (for more information see the section on
Validation), for type conversion errors you would want a message to use for the error inside the grails-app/i18n/messages.properties file. You can use a generic error message handler such as:
typeMismatch.java.net.URL=The field {0} is not a valid URLOr a more specific one:
typeMismatch.Book.publisherURL=The publisher URL you specified is not a valid URL
Data Binding and Security concerns
When batch updating properties from request parameters you need to be careful not to allow clients to bind malicious data to domain classes that end up being persisted to the database. You can limit what properties are bound to a given domain class using the subscript operator:
def p = Person.get(1)p.properties['firstName','lastName'] = params
In this case only the
firstName and
lastName properties will be bound.
Another way to do this is instead of using domain classes as the target of data binding you could use
Command Objects. Alternatively there is also the flexible
bindData method.
The
bindData method allows the same data binding capability, but to arbitrary objects:
def p = new Person()
bindData(p, params)
However, the
bindData method also allows you to exclude certain parameters that you don't want updated:
def p = new Person()
bindData(p, params, [exclude:'dateOfBirth'])
Or include only certain properties:
def p = new Person()
bindData(p, params, [include:['firstName','lastName]])
Using the render method to output XML
Grails' supports a few different ways to produce XML and JSON responses. The first one covered is via the
render method.
The
render method can be passed a block of code to do mark-up building in XML:
def list = {
def results = Book.list()
render(contentType:"text/xml") {
books {
for(b in results) {
book(title:b.title)
}
}
}
}The result of this code would be something like:
<books>
<book title="The Stand" />
<book title="The Shining" />
</books>
Note that you need to be careful to avoid naming conflicts when using mark-up building. For example this code would produce an error:
def list = {
def books = Book.list() // naming conflict here
render(contentType:"text/xml") {
books {
for(b in results) {
book(title:b.title)
}
}
}
}The reason is that there is local variable
books which Groovy attempts to invoke as a method.
Using the render method to output JSON
The
render method can also be used to output JSON:
def list = {
def results = Book.list()
render(contentType:"text/json") {
books = array {
for(b in results) {
book title:b.title
}
}
}
}In this case the result would be something along the lines of:
[
{title:"The Stand"},
{title:"The Shining"}
]Again the same dangers with naming conflicts apply to JSON building.
Automatic XML Marshalling
Grails also supports automatic marshaling of
domain classes to XML via special converters.
To start off with import the
grails.converters package into your controller:
import grails.converters.*
Now you can use the following highly readable syntax to automatically convert domain classes to XML:
render Book.list() as XML
The resulting output would look something like the following::
<?xml version="1.0" encoding="ISO-8859-1"?>
<list>
<book id="1">
<author>Stephen King</author>
<title>The Stand</title>
</book>
<book id="2">
<author>Stephen King</author>
<title>The Shining</title>
</book>
</list>An alternative to using the converters is to use the
codecs feature of Grails. The codecs feature provides
encodeAsXML and
encodeAsJSON methods:
def xml = Book.list().encodeAsXML()
render xml
For more information on XML marshaling see the section on
RESTAutomatic JSON Marshalling
Grails also supports automatic marshaling to JSON via the same mechanism. Simply substitute
XML with
JSON:
render Book.list() as JSON
The resulting output would look something like the following:
[
{"id":1,
"class":"Book",
"author":"Stephen King",
"title":"The Stand"},
{"id":2,
"class":"Book",
"author":"Stephen King",
"releaseDate":new Date(1194127343161),
"title":"The Shining"}
]Again as an alternative you can use the
encodeAsJSON to achieve the same effect.
The previous section on on XML and JSON responses covered simplistic examples of rendering XML and JSON responses. Whilst the XML builder used by Grails is the standard
XmlSlurper found in Groovy, the JSON builder is a custom implementation specific to Grails.
JSONBuilder and Grails versions
JSONBuilder behaves different depending on the version of Grails you use. For version below 1.2 there deprecated
grails.util.JSonBuilder class is used. This section covers the usage of the Grails 1.2 JSONBuilder
For backwards compatibility the old
JSonBuilder class is used with the
render method for older applications, if you want to use the newer/better
JSONBuilder class then you can do so by setting the following in
Config.groovy:
grails.json.legacy.builder=false
Rendering Simple Objects
To render a simple JSON object just set properties within the context of the closure:
render(contentType:"text/json") {
hello = "world"
}The above will produce the JSON:
Rendering JSON Arrays
To render a list of objects simple assign a list:
render(contentType:"text/json") {
categories = ['a', 'b', 'c']
}This will produce:
{"categories":["a","b","c"]}You can also render lists of complex objects, for example:
render(contentType:"text/json") {
categories = [ { a = "A" }, { b = "B" } ]
}This will produce:
{"categories":[ {"a":"A"} , {"b":"B"}] }If you want to return a list as the root then you have to use the special
element method:
render(contentType:"text/json") {
element 1
element 2
element 3
}The above code produces:
Rendering Complex Objects
Rendering complex objects can be done with closures. For example:
render(contentType:"text/json") {
categories = ['a', 'b', 'c']
title ="Hello JSON"
information = {
pages = 10
}
}The above will produce the JSON:
{"categories":["a","b","c"],"title":"Hello JSON","information":{"pages":10}}Arrays of Complex Objects
As mentioned previously you can nest complex objects within arrays using closures:
render(contentType:"text/json") {
categories = [ { a = "A" }, { b = "B" } ]
}However, if you need to build them up dynamically then you may want to use the
array method:
def results = Book.list()
render(contentType:"text/json") {
books = array {
for(b in results) {
book title:b.title
}
}
}Direct JSONBuilder API Access
If you don't have access to the
render method, but still want to produce JSON you can use the API directly:
def builder = new JSONBuilder()def result = builder.build {
categories = ['a', 'b', 'c']
title ="Hello JSON"
information = {
pages = 10
}
}// prints the JSON text
println result.toString()def sw = new StringWriter()
result.render swProgrammatic File Uploads
Grails supports file uploads via Spring's
MultipartHttpServletRequest interface. To upload a file the first step is to create a multipart form like the one below:
Upload Form: <br />
<g:form action="upload" method="post" enctype="multipart/form-data">
<input type="file" name="myFile" />
<input type="submit" />
</g:form>
There are then a number of ways to handle the file upload. The first way is to work with the Spring
MultipartFile instance directly:
def upload = {
def f = request.getFile('myFile')
if(!f.empty) {
f.transferTo( new File('/some/local/dir/myfile.txt') )
response.sendError(200,'Done');
}
else {
flash.message = 'file cannot be empty'
render(view:'uploadForm')
}
}This is clearly handy for doing transfers to other destinations and manipulating the file directly as you can obtain an InputStream and so on via the
MultipartFile interface.
File Uploads through Data Binding
File uploads can also be performed via data binding. For example say you have an
Image domain class as per the below example:
class Image {
byte[] myFile
}Now if you create an image and pass in the
params object such as the below example, Grails will automatically bind the file's contents as a byte to the
myFile property:
def img = new Image(params)
It is also possible to set the contents of the file as a string by changing the type of the
myFile property on the image to a String type:
class Image {
String myFile
}Grails controllers support the concept of command objects. A command object is similar to a form bean in something like Struts and they are useful in circumstances when you want to populate a subset of the properties needed to update a domain class. Or where there is no domain class required for the interaction, but you need features such as
data binding and
validation.
Declaring Command Objects
Command objects are typically declared in the same source file as a controller directly below the controller class definition. For example:
class UserController {
…
}
class LoginCommand {
String username
String password
static constraints = {
username(blank:false, minSize:6)
password(blank:false, minSize:6)
}
}As the previous example demonstrates you can supply
constraints to command objects just as you can with
domain classes.
Using Command Objects
To use command objects, controller actions may optionally specify any number of command object parameters. The parameter types must be supplied so that Grails knows what objects to create, populate and validate.
Before the controller action is executed Grails will automatically create an instance of the command object class, populate the properties of the command object with request parameters having corresponding names and the command object will be validated. For Example:
class LoginController {
def login = { LoginCommand cmd ->
if(cmd.hasErrors()) {
redirect(action:'loginForm')
}
else {
// do something else
}
}
}Command Objects and Dependency Injection
Command objects can participate in dependency injection. This is useful if your command object has some custom validation logic which may need to interact with Grails
services:
class LoginCommand {
def loginService String username
String password static constraints = {
username(validator: { val, obj ->
obj.loginService.canLogin(obj.username, obj.password)
})
}
}In this example the command object interacts with a bean injected by name from the Spring
ApplicationContext.
Grails has built in support for handling duplicate form submissions using the "Synchronizer Token Pattern". To get started you need to define a token on the
form tag:
<g:form useToken="true" ...>
Then in your controller code you can use the
withForm method to handle valid and invalid requests:
withForm {
// good request
}.invalidToken {
// bad request
}If you only provide the
withForm method and not the chained
invalidToken method then by default Grails will store the invalid token in a
flash.invalidToken variable and redirect the request back to the original page. This can then be checked in the view:
<g:if test="${flash.invalidToken}">
Don't click the button twice!
</g:if>
The withForm tag makes use of the session and hence requires session affinity if used in a cluster.
Type Conversion Methods
If you prefer to avoid the overhead of
Data Binding and simply want to convert incoming parameters (typically Strings) into another more appropriate type the
params object has a number of convenience methods for each type:
def total = params.int('total')The above example uses the
int method, there are also methods for
boolean,
long,
char,
short and so on. Each of these methods are null safe and safe from any parsing errors so you don't have to perform any addition checks on the parameters.
These same type conversion methods are also available on the tagLibraries parameter of GSP tags.
Handling Multi Parameters
A common use case is dealing with multiple request parameters of the same name. For example you could get a query string such as
?name=Bob&name=Judy.
In this case dealing with 1 parameter and dealing with many has different semantics since Groovy's iteration mechanics for
String iterate over each character. To avoid this problem the
params object provides a
list method that always returns a list:
for(name in params.list('name')) {
println name
}Groovy Servers Pages (or GSP for short) is Grails' view technology. It is designed to be familiar for users of technologies such as ASP and JSP, but to be far more flexible and intuitive.
In Grails GSPs live in the
grails-app/views directory and are typically rendered automatically (by convention) or via the
render method such as:
A GSP is typically a mix of mark-up and GSP tags which aid in view rendering.
Although it is possible to have Groovy logic embedded in your GSP and doing this will be covered in this document the practice is strongly discouraged. Mixing mark-up and code is a bad thing and most GSP pages contain no code and needn't do so.
A GSP typically has a "model" which is a set of variables that are used for view rendering. The model is passed to the GSP view from a controller. For example consider the following controller action:
def show = {
[book: Book.get(params.id)]
}This action will look-up a
Book instance and create a model that contains a key called
book. This key can then be reference within the GSP view using the name
book:
In the next view sections we'll go through the basics of GSP and what is available to you. First off let's cover some basic syntax that users of JSP and ASP should be familiar with.
GSP supports the usage of
<% %> blocks to embed Groovy code (again this is discouraged):
<html>
<body>
<% out << "Hello GSP!" %>
</body>
</html>As well as this syntax you can also use the
<%= %> syntax to output values:
<html>
<body>
<%="Hello GSP!" %>
</body>
</html>
GSP also supports JSP-style server-side comments as the following example demonstrates:
<html>
<body>
<%-- This is my comment --%>
<%="Hello GSP!" %>
</body>
</html>Within the
<% %> brackets you can of course declare variables:
And then re-use those variables further down the page:
However, within the scope of a GSP there are a number of pre-defined variables including:
Using the
<% %> syntax you can of course embed loops and so on using this syntax:
<html>
<body>
<% [1,2,3,4].each { num -> %>
<p><%="Hello ${num}!" %></p>
<%}%>
</body>
</html>As well as logical branching:
<html>
<body>
<% if(params.hello == 'true' )%>
<%="Hello!"%>
<% else %>
<%="Goodbye!"%>
</body>
</html>GSP also supports a few JSP-style page directives.
The import directive allows you to import classes into the page. However, it is rarely needed due to Groovy's default imports and
GSP Tags:
<%@ page import="java.awt.*" %>
GSP also supports the contentType directive:
<%@ page contentType="text/json" %>
The contentType directive allows using GSP to render other formats.
In GSP the
<%= %> syntax introduced earlier is rarely used due to the support for GSP expressions. It is present mainly to allow ASP and JSP developers to feel at home using GSP. A GSP expression is similar to a JSP EL expression or a Groovy GString and takes the form
${expr}:
<html>
<body>
Hello ${params.name}
</body>
</html>However, unlike JSP EL you can have any Groovy expression within the
${..} parenthesis. Variables within the
${..} are
not escaped by default, so any HTML in the variable's string is output directly to the page. To reduce the risk of Cross-site-scripting (XSS) attacks, you can enable automatic HTML escaping via the
grails.views.default.codec setting in
grails-app/conf/Config.groovy:
grails.views.default.codec='html'
Other possible values are 'none' (for no default encoding) and 'base64'.
Now that the less attractive JSP heritage has been set aside, the following sections cover GSP's built-in tags, which are the favored way to define GSP pages.
The section on Tag Libraries covers how to add your own custom tag libraries.
All built-in GSP tags start with the prefix
g:. Unlike JSP, you don't need to specify any tag library imports. If a tag starts with
g: it is automatically assumed to be a GSP tag. An example GSP tag would look like:
GSP tags can also have a body such as:
<g:example>
Hello world
</g:example>
Expressions can be passed into GSP tag attributes, if an expression is not used it will be assumed to be a String value:
<g:example attr="${new Date()}">
Hello world
</g:example>Maps can also be passed into GSP tag attributes, which are often used for a named parameter style syntax:
<g:example attr="${new Date()}" attr2="[one:1, two:2, three:3]">
Hello world
</g:example>Note that within the values of attributes you must use single quotes for Strings:
<g:example attr="${new Date()}" attr2="[one:'one', two:'two']">
Hello world
</g:example>With the basic syntax out the way, the next sections look at the tags that are built into Grails by default.
Variables can be defined within a GSP using the
set tag:
<g:set var="now" value="${new Date()}" />Here we assign a variable called
now to the result of a GSP expression (which simply constructs a new
java.util.Date instance). You can also use the body of the
<g:set> tag to define a variable:
<g:set var="myHTML">
Some re-usable code on: ${new Date()}
</g:set>Variables can also be placed in one of the following scopes:
page - Scoped to the current page (default)request - Scoped to the current requestflash - Placed within flash scope and hence available for the next requestsession - Scoped for the user sessionapplication - Application-wide scope.
To select which scope a variable is placed into use the
scope attribute:
<g:set var="now" value="${new Date()}" scope="request" />GSP also supports logical and iterative tags out of the box. For logic there are
if,
else and
elseif which support your typical branching scenarios:
<g:if test="${session.role == 'admin'}">
<%-- show administrative functions --%>
</g:if>
<g:else>
<%-- show basic functions --%>
</g:else>For iteration GSP has the
each and
while tags:
<g:each in="${[1,2,3]}" var="num">
<p>Number ${num}</p>
</g:each><g:set var="num" value="${1}" />
<g:while test="${num < 5 }">
<p>Number ${num++}</p>
</g:while>If you have collections of objects you often need to sort and filter them in some way. GSP supports the
findAll and
grep for this task:
Stephen King's Books:
<g:findAll in="${books}" expr="it.author == 'Stephen King'">
<p>Title: ${it.title}</p>
</g:findAll>The
expr attribute contains a Groovy expression that can be used as a filter. Speaking of filters the
grep tag does a similar job such as filter by class:
<g:grep in="${books}" filter="NonFictionBooks.class">
<p>Title: ${it.title}</p>
</g:grep>Or using a regular expression:
<g:grep in="${books.title}" filter="~/.*?Groovy.*?/">
<p>Title: ${it}</p>
</g:grep>The above example is also interesting due to its usage of GPath. GPath is Groovy's equivalent to an XPath like language. Essentially the
books collection is a collection of
Book instances. However assuming each
Book has a
title, you can obtain a list of Book titles using the expression
books.title. Groovy will auto-magically go through the list of Book instances, obtain each title, and return a new list!
GSP also features tags to help you manage linking to controllers and actions. The
link tag allows you to specify controller and action name pairing and it will automatically work out the link based on the
URL Mappings, even if you change them! Some examples of the
link can be seen below:
<g:link action="show" id="1">Book 1</g:link>
<g:link action="show" id="${currentBook.id}">${currentBook.name}</g:link>
<g:link controller="book">Book Home</g:link>
<g:link controller="book" action="list">Book List</g:link>
<g:link url="[action:'list',controller:'book']">Book List</g:link>
<g:link action="list" params="[sort:'title',order:'asc',author:currentBook.author]">
Book List
</g:link>Form Basics
GSP supports many different tags for aiding in dealing with HTML forms and fields, the most basic of which is the
form tag. The
form tag is a controller/action aware version of the regular HTML form tag. The
url attribute allows you to specify which controller and action to map to:
<g:form name="myForm" url="[controller:'book',action:'list']">...</g:form>
In this case we create a form called
myForm that submits to the
BookController's
list action. Beyond that all of the usual HTML attributes apply.
Form Fields
As well as easy construction of forms GSP supports custom tags for dealing with different types of fields including:
- textField - For input fields of type 'text'
- checkBox - For input fields of type 'checkbox'
- radio - For input fields of type 'radio'
- hiddenField - For input fields of type 'hidden'
- select - For dealing with HTML select boxes
Each of these allow GSP expressions as the value:
<g:textField name="myField" value="${myValue}" />GSP also contains extended helper versions of the above tags such as
radioGroup (for creating groups of
radio tags),
localeSelect,
currencySelect and
timeZoneSelect (for selecting locale's, currencies and time zone's respectively).
Multiple Submit Buttons
The age old problem of dealing with multiple submit buttons is also handled elegantly with Grails via the
actionSubmit tag. It is just like a regular submit, but allows you to specify an alternative action to submit to:
<g:actionSubmit value="Some update label" action="update" />
One major different between GSP tags and other tagging technologies is that GSP tags can be called as either regular tags or as method calls from either
controllers,
tag libraries or GSP views.
Tags as method calls from GSPs
When called as methods tags return their results as a String instead of writing directly to the response. So for example the
createLinkTo tag can equally be called as a method:
Static Resource: ${createLinkTo(dir:"images", file:"logo.jpg")}This is particularly useful when you need to use a tag within an attribute:
<img src="${createLinkTo(dir:'images', file:'logo.jpg')}" />In view technologies that don't support this feature you have to nest tags within tags, which becomes messy quickly and often has an adverse effect of WYSWIG tools such as Dreamweaver that attempt to render the mark-up as it is not well-formed:
<img src="<g:createLinkTo dir="images" file="logo.jpg" />" />
Tags as method calls from Controllers and Tag Libraries
You can also invoke tags from controllers and tag libraries. Tags within the default
g: namespace can be invoked without the prefix and a String result is returned:
def imageLocation = createLinkTo(dir:"images", file:"logo.jpg")
However, you can also prefix the namespace to avoid naming conflicts:
def imageLocation = g.createLinkTo(dir:"images", file:"logo.jpg")
If you have a
custom namespace you can use that prefix instead (Example using the
FCK Editor plugin):
def editor = fck.editor()
As well as views, Grails has the concept of templates. Templates are useful for separating out your views into maintainable chunks and combined with
Layouts provide a highly re-usable mechanism for structure views.
Template Basics
Grails uses the convention of placing an underscore before the name of a view to identify it as a template. For example a you may have a template that deals with rendering Books located at
grails-app/views/book/_bookTemplate.gsp:
<div class="book" id="${book?.id}">
<div>Title: ${book?.title}</div>
<div>Author: ${book?.author?.name}</div>
</div>To render this template from one of the views in
grails-app/views/book you can use the
render tag:
<g:render template="bookTemplate" model="[book:myBook]" />
Notice how we pass into a model to use using the
model attribute of the render tag. If you have multiple
Book instances you can also render the template for each
Book using the render tag:
<g:render template="bookTemplate" var="book" collection="${bookList}" />Shared Templates
In the previous example we had a template that was specific to the
BookController and its views at
grails-app/views/book. However, you may want to share templates across your application.
In this case you can place them in the root views directory at grails-app/views or any subdirectory below that location and then with the template attribute use a
/ before the template name to indicate the relative template path. For example if you had a template called
grails-app/views/shared/_mySharedTemplate.gsp, you could reference it as follows:
<g:render template="/shared/mySharedTemplate" />
You can also use this technique to reference templates in any directory from any view or controller:
<g:render template="/book/bookTemplate" model="[book:myBook]" />
The Template Namespace
Since templates are used so frequently there is template namespace, called
tmpl, available that makes using templates easier. Consider for example the following usage pattern:
<g:render template="bookTemplate" model="[book:myBook]" />
This can be expressed with the
tmpl namespace as follows:
<tmpl:bookTemplate book="${myBook}" />Templates in Controllers and Tag Libraries
You can also render templates from controllers using the
render method found within controllers, which is useful for
Ajax applications:
def show = {
def b = Book.get(params.id)
render(template:"bookTemplate", model:[book:b])
}The
render method within controllers writes directly to the response, which is the most common behaviour. If you need to instead obtain the result of template as a String you can use the
render tag:
def show = {
def b = Book.get(params.id)
String content = g.render(template:"bookTemplate", model:[book:b])
render content
}Notice the usage of the
g. namespace which tells Grails we want to use the
tag as method call instead of the
render method.
Creating Layouts
Grails leverages
Sitemesh, a decorator engine, to support view layouts. Layouts are located in the
grails-app/views/layouts directory. A typical layout can be seen below:
<html>
<head>
<title><g:layoutTitle default="An example decorator" /></title>
<g:layoutHead />
</head>
<body onload="${pageProperty(name:'body.onload')}">
<div class="menu"></menu>
<div class="body">
<g:layoutBody />
</div>
</div>
</body>
</html>The key elements are the
layoutHead,
layoutTitle and
layoutBody tag usages, here is what they do:
layoutTitle - outputs the target page's titlelayoutHead - outputs the target pages head tag contentslayoutBody - outputs the target pages body tag contents
The previous example also demonstrates the
pageProperty tag which can be used to inspect and return aspects of the target page.
Triggering Layouts
There are a few ways to trigger a layout. The simplest is to add a meta tag to the view:
<html>
<head>
<title>An Example Page</title>
<meta name="layout" content="main"></meta>
</head>
<body>This is my content!</body>
</html>In this case a layout called
grails-app/views/layouts/main.gsp will be used to layout the page. If we were to use the layout from the previous section the output would resemble the below:
<html>
<head>
<title>An Example Page</title>
</head>
<body onload="">
<div class="menu"></div>
<div class="body">
This is my content!
</div>
</body>
</html>Specifying A Layout In A Controller
Another way to specify a layout is to specify the name of the layout by assigning a value to the "layout" property in a controller. For example, if you have a controller such as:
class BookController {
static layout = 'customer' def list = { … }
}You can create a layout called
grails-app/views/layouts/customer.gsp which will be applied to all views that the
BookController delegates to. The value of the "layout" property may contain a directory structure relative to the
grails-app/views/layouts/ directory. For example:
class BookController {
static layout = 'custom/customer' def list = { … }
}Views rendered from that controller would be decorated with the
grails-app/views/layouts/custom/customer.gsp template.
Layout by Convention
Another way to associate layouts is to use "layout by convention". For example, if you have a controller such as:
class BookController {
def list = { … }
}You can create a layout called
grails-app/views/layouts/book.gsp, by convention, which will be applied to all views that the
BookController delegates to.
Alternatively, you can create a layout called
grails-app/views/layouts/book/list.gsp which will only be applied to the
list action within the
BookController.
If you have both the above mentioned layouts in place the layout specific to the action will take precedence when the list action is executed.
Inline Layouts
Grails' also supports Sitemesh's concept of inline layouts with the
applyLayout tag. The
applyLayout tag can be used to apply a layout to a template, URL or arbitrary section of content. Essentially, this allows to even further modularize your view structure by "decorating" your template includes.
Some examples of usage can be seen below:
<g:applyLayout name="myLayout" template="bookTemplate" collection="${books}" /><g:applyLayout name="myLayout" url="http://www.google.com" /><g:applyLayout name="myLayout">
The content to apply a layout to
</g:applyLayout>Server-Side Includes
While the
applyLayout tag is useful for applying layouts to external content, if you simply want to include external content in the current page you can do so with the
include:
<g:include controller="book" action="list"></g:include>
You can even combine the
include tag and the
applyLayout tag for added flexibility:
<g:applyLayout name="myLayout">
<g:include controller="book" action="list"></g:include>
</g:applyLayout>
Finally, you can also call the
include tag from a controller or tag library as a method:
def content = include(controller:"book", action:"list")
The resulting content will be provided via the return value of the
include tag.
Although it is useful to decorate an entire page sometimes you may find the need to decorate independent sections of your site. To do this you can use content blocks. To get started you need to divide the page to be decorate using the
<content> tag:
<content tag="navbar">
… draw the navbar here…
</content>
<content tag="header">
… draw the header here…
</content>
<content tag="footer">
… draw the footer here…
</content>
<content tag="body">
… draw the body here…
</content>
Then within the layout you can reference these components and apply individual layouts to each:
<html>
<body>
<div id="header">
<g:applyLayout name="headerLayout"><g:pageProperty name="page.header"></g:applyLayout>
</div>
<div id="nav">
<g:applyLayout name="navLayout"><g:pageProperty name="page.navbar"></g:applyLayout>
</div>
<div id="body">
<g:applyLayout name="bodyLayout"><g:pageProperty name="page.body"></g:applyLayout>
</div>
<div id="footer">
<g:applyLayout name="footerLayout"><g:pageProperty name="page.footer"></g:applyLayout>
</div>
</body>
</html>
One of the main issues with deploying a Grails application (or typically any servlet-based one) is that any change to the views requires you to redeploy your whole application. If all you want to do is fix a typo on a page, or change an image link, it can seem like a lot of unnecessary work. For such simple requirements, Grails does have a solution: the
grails.gsp.view.dir configuration setting.
How does this work? The first step is to decide where the GSP files should go. Let's say we want to keep them unpacked in a
/var/www/grails/my-app directory. We add these two lines to
grails-app/conf/Config.groovy :
grails.gsp.enable.reload = true
grails.gsp.view.dir = "/var/www/grails/my-app/"
The first line tells Grails that modified GSP files should be reloaded at runtime. If you don't have this setting, you can make as many changes as you like but they won't be reflected in the running application. The second line tells Grails where to load the views and layouts from.
The trailing slash on the grails.gsp.view.dir value is important! Without it, Grails will look for views in the parent directory.
With those settings in place, all you need to do is copy the views from your web application to the external directory. On a Unix-like system, this would look something like this:
mkdir -p /var/www/grails/my-app/grails-app/views
cp -R grails-app/views/* /var/www/grails/my-app/grails-app/views
The key point here is that you must retain the view directory structure, including the
grails-app/views bit. So you end up with the path
/var/www/grails/my-app/grails-app/views/... .
One thing to bear in mind with this technique is that every time you modify a GSP, it uses up permgen space. So at some point you will eventually hit "out of permgen space" errors unless you restart the server. So this technique is not recommended for frequent or large changes to the views.
Like
Java Server Pages (JSP), GSP supports the concept of custom tag libraries. Unlike JSP, Grails tag library mechanism is simply, elegant and completely reload-able at runtime.
Quite simply, to create a tag library create a Groovy class that ends with the convention
TagLib and place it within the
grails-app/taglib directory:
Now to create a tag simply create property that is assigned a block of code that takes two arguments: The tag attributes and the body content:
class SimpleTagLib {
def simple = { attrs, body -> }
}The
attrs argument is a simple map of the attributes of the tag, whilst the
body argument is another invokable block of code that returns the body content:
class SimpleTagLib {
def emoticon = { attrs, body ->
out << body() << (attrs.happy == 'true' ? " :-)" : " :-(")
}
}As demonstrated above there is an implicit
out variable that refers to the output
Writer which you can use to append content to the response. Then you can simply reference the tag inside your GSP, no imports necessary:
<g:emoticon happy="true">Hi John</g:emoticon>
Within the scope of a tag library there are a number of pre-defined variables including:
actionName - The currently executing action namecontrollerName - The currently executing controller nameflash - The flash objectgrailsApplication - The GrailsApplication instanceout - The response writer for writing to the output streampageScope - A reference to the pageScope object used for GSP rendering (i.e. the binding)params - The params object for retrieving request parameterspluginContextPath - The context path to the plugin that contains the tag libraryrequest - The HttpServletRequest instanceresponse - The HttpServletResponse instanceservletContext - The javax.servlet.ServletContext instancesession - The HttpSession instance
As demonstrated it the previous example it is trivial to write simple tags that have no body and merely output content. Another example is a
dateFormat style tag:
def dateFormat = { attrs, body ->
out << new java.text.SimpleDateFormat(attrs.format).format(attrs.date)
}The above uses Java's
SimpleDateFormat class to format a date and then write it to the response. The tag can then be used within a GSP as follows:
<g:dateFormat format="dd-MM-yyyy" date="${new Date()}" />With simple tags sometimes you need to write HTML mark-up to the response. One approach would be to embed the content directly:
def formatBook = { attrs, body ->
out << "<div id="${attrs.book.id}">"
out << "Title : ${attrs.book.title}"
out << "</div>"
}Although this approach may be tempting it is not very clean. A better approach would be to re-use the
render tag:
def formatBook = { attrs, body ->
out << render(template:"bookTemplate", model:[book:attrs.book])
}And then have a separate GSP template that does the actual rendering.
You can also create logical tags where the body of the tag is only output once a set of conditions have been met. An example of this may be a set of security tags:
def isAdmin = { attrs, body ->
def user = attrs['user']
if(user != null && checkUserPrivs(user)) {
out << body()
}
}The tag above checks if the user is an administrator and only outputs the body content if he/she has the correct set of access privileges:
<g:isAdmin user="${myUser}">
// some restricted content
</g:isAdmin>Iterative tags are trivial too, since you can invoke the body multiple times:
def repeat = { attrs, body ->
attrs.times?.toInteger().times { num ->
out << body(num)
}
}In this example we check for a
times attribute and if it exists convert it to a number then use Groovy's
times method to iterate by the number of times specified by the number:
<g:repeat times="3">
<p>Repeat this 3 times! Current repeat = ${it}</p>
</g:repeat>Notice how in this example we use the implicit
it variable to refer to the current number. This works because when we invoked the body we passed in the current value inside the iteration:
That value is then passed as the default variable
it to the tag. However, if you have nested tags this can lead to conflicts, hence you should should instead name the variables that the body uses:
def repeat = { attrs, body ->
def var = attrs.var ? attrs.var : "num"
attrs.times?.toInteger().times { num ->
out << body((var):num)
}
}Here we check if there is a
var attribute and if there is use that as the name to pass into the body invocation on this line:
Note the usage of the parenthesis around the variable name. If you omit these Groovy assumes you are using a String key and not referring to the variable itself.
Now we can change the usage of the tag as follows:
<g:repeat times="3" var="j">
<p>Repeat this 3 times! Current repeat = ${j}</p>
</g:repeat>Notice how we use the
var attribute to define the name of the variable
j and then we are able to reference that variable within the body of the tag.
By default, tags are added to the default Grails namespace and are used with the
g: prefix in GSP pages. However, you can specify a different namespace by adding a static property to your
TagLib class:
class SimpleTagLib {
static namespace = "my" def example = { attrs ->
…
}
}Here we have specified a
namespace of
my and hence the tags in this tag lib must then be referenced from GSP pages like this:
<my:example name="..." />
Where the prefix is the same as the value of the static
namespace property. Namespaces are particularly useful for plugins.
Tags within namespaces can be invoked as methods using the namespace as a prefix to the method call:
out << my.example(name:"foo")
This works from GSP, controllers or tag libraries
In addition to the simplified tag library mechanism provided by GSP, you can also use JSP tags from GSP. To do so simply declare the JSP you want to use via the
taglib directive:
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>
Then you can use it like any other tag:
<fmt:formatNumber value="${10}" pattern=".00"/>With the added bonus that you can invoke JSP tags like methods:
${fmt.formatNumber(value:10, pattern:".00")}Since Grails 1.2, a tag library call returns an instance of
org.codehaus.groovy.grails.web.util.StreamCharBuffer class by default.
This change improves performance by reducing object creation and optimizing buffering during request processing.
In earlier Grails versions, a
java.lang.String instance was returned.
Tag libraries can also return direct object values to the caller since Grails 1.2..
Object returning tag names are listed in a static
returnObjectForTags property in the tag library class.
Example:
class ObjectReturningTagLib {
static namespace = "cms"
static returnObjectForTags = ['content'] def content = { attrs, body ->
CmsContent.findByCode(attrs.code)?.content
}
}Throughout the documentation so far the convention used for URLs has been the default of
/controller/action/id. However, this convention is not hard wired into Grails and is in fact controlled by a URL Mappings class located at
grails-app/conf/UrlMappings.groovy.
The
UrlMappings class contains a single property called
mappings that has been assigned a block of code:
class UrlMappings {
static mappings = {
}
}To create a simple mapping simply use a relative URL as the method name and specify named parameters for the controller and action to map to:
"/product"(controller:"product", action:"list")
In this case we've mapped the URL
/product to the
list action of the
ProductController. You could of course omit the action definition to map to the default action of the controller:
"/product"(controller:"product")
An alternative syntax is to assign the controller and action to use within a block passed to the method:
"/product" {
controller = "product"
action = "list"
}Which syntax you use is largely dependent on personal preference. If you simply want to rewrite on URI onto another explicit URI (rather than a controller/action pair) this can be achieved with the following example:
"/hello"(uri:"/hello.dispatch")
Rewriting specific URIs is often useful when integrating with other frameworks.
Simple Variables
The previous section demonstrated how to map trivial URLs with concrete "tokens". In URL mapping speak tokens are the sequence of characters between each slash / character. A concrete token is one which is well defined such as as
/product. However, in many circumstances you don't know what the value of a particular token will be until runtime. In this case you can use variable placeholders within the URL for example:
static mappings = {
"/product/$id"(controller:"product")
}In this case by embedding a $id variable as the second token Grails will automatically map the second token into a parameter (available via the
params object) called
id. For example given the URL
/product/MacBook, the following code will render "MacBook" to the response:
class ProductController {
def index = { render params.id }
}
You can of course construct more complex examples of mappings. For example the traditional blog URL format could be mapped as follows:
static mappings = {
"/$blog/$year/$month/$day/$id"(controller:"blog", action:"show")
}The above mapping would allow you to do things like:
/graemerocher/2007/01/10/my_funky_blog_entry
The individual tokens in the URL would again be mapped into the
params object with values available for
year,
month,
day,
id and so on.
Dynamic Controller and Action Names
Variables can also be used to dynamically construct the controller and action name. In fact the default Grails URL mappings use this technique:
static mappings = {
"/$controller/$action?/$id?"()
}Here the name of the controller, action and id are implicitly obtained from the variables
controller,
action and
id embedded within the URL.
You can also resolve the controller name and action name to execute dynamically using a closure:
static mappings = {
"/$controller" {
action = { params.goHere }
}
}Optional Variables
Another characteristic of the default mapping is the ability to append a
? at the end of a variable to make it an optional token. In a further example this technique could be applied to the blog URL mapping to have more flexible linking:
static mappings = {
"/$blog/$year?/$month?/$day?/$id?"(controller:"blog", action:"show")
}With this mapping all of the below URLs would match with only the relevant parameters being populated in the
params object:
/graemerocher/2007/01/10/my_funky_blog_entry
/graemerocher/2007/01/10
/graemerocher/2007/01
/graemerocher/2007
/graemerocher
Arbitrary Variables
You can also pass arbitrary parameters from the URL mapping into the controller by merely setting them in the block passed to the mapping:
"/holiday/win" {
id = "Marrakech"
year = 2007
}This variables will be available within the
params object passed to the controller.
Dynamically Resolved Variables
The hard coded arbitrary variables are useful, but sometimes you need to calculate the name of the variable based on runtime factors. This is also possible by assigning a block to the variable name:
"/holiday/win" {
id = { params.id }
isEligible = { session.user != null } // must be logged in
}In the above case the code within the blocks is resolved when the URL is actually matched and hence can be used in combination with all sorts of logic.
If you want to resolve a URL to a view, without a controller or action involved, you can do so too. For example if you wanted to map the root URL
/ to a GSP at the location
grails-app/views/index.gsp you could use:
static mappings = {
"/"(view:"/index") // map the root URL
}Alternatively if you need a view that is specific to a given controller you could use:
static mappings = {
"/help"(controller:"site",view:"help") // to a view for a controller
}Grails also allows you to map HTTP response codes to controllers, actions or views. All you have to do is use a method name that matches the response code you are interested in:
static mappings = {
"500"(controller:"errors", action:"serverError")
"404"(controller:"errors", action:"notFound")
"403"(controller:"errors", action:"forbidden")
}Or alternatively if you merely want to provide custom error pages:
static mappings = {
"500"(view:"/errors/serverError")
"404"(view:"/errors/notFound")
"403"(view:"/errors/forbidden")
}URL mappings can also be configured to map based on the HTTP method (GET, POST, PUT or DELETE). This is extremely useful for RESTful APIs and for restricting mappings based on HTTP method.
As an example the following mappings provide a RESTful API URL mappings for the
ProductController:
static mappings = {
"/product/$id"(controller:"product"){
action = [GET:"show", PUT:"update", DELETE:"delete", POST:"save"]
}
}Grails' URL mappings mechanism also supports wildcard mappings. For example consider the following mapping:
static mappings = {
"/images/*.jpg"(controller:"image")
}This mapping will match all paths to images such as
/image/logo.jpg. Of course you can achieve the same effect with a variable:
static mappings = {
"/images/$name.jpg"(controller:"image")
}However, you can also use double wildcards to match more than one level below:
static mappings = {
"/images/**.jpg"(controller:"image")
}In this cases the mapping will match
/image/logo.jpg as well as
/image/other/logo.jpg. Even better you can use a double wildcard variable:
static mappings = {
// will match /image/logo.jpg and /image/other/logo.jpg
"/images/$name**.jpg"(controller:"image")
}In this case it will store the path matched by the wildcard inside a
name parameter obtainable from the
params object:
def name = params.name
println name // prints "logo" or "other/logo"
If you are using wildcard URL mappings then you may want to exclude certain URIs from Grails' URL mapping process. To do this you can provide an
excludes setting inside the
UrlMappings.groovy class:
class UrlMappings = {
static excludes = ["/images/**", "/css/**"]
static mappings = {
…
}
}In this case Grails won't attempt to match any URIs that start with
/images or
/css.
Another great feature of URL mappings is that they automatically customize the behaviour of the
link tag so that changing the mappings don't require you to go and change all of your links.
This is done through a URL re-writing technique that reverse engineers the links from the URL mappings. So given a mapping such as the blog one from an earlier section:
static mappings = {
"/$blog/$year?/$month?/$day?/$id?"(controller:"blog", action:"show")
}If you use the link tag as follows:
<g:link controller="blog" action="show" params="[blog:'fred', year:2007]">My Blog</g:link>
<g:link controller="blog" action="show" params="[blog:'fred', year:2007, month:10]">My Blog - October 2007 Posts</g:link>
Grails will automatically re-write the URL in the correct format:
<a href="/fred/2007">My Blog</a>
<a href="/fred/2007/10">My Blog - October 2007 Posts</a>
URL Mappings also support Grails' unified
validation constraints mechanism, which allows you to further "constrain" how a URL is matched. For example, if we revisit the blog sample code from earlier, the mapping currently looks like this:
static mappings = {
"/$blog/$year?/$month?/$day?/$id?"(controller:"blog", action:"show")
}This allows URLs such as:
/graemerocher/2007/01/10/my_funky_blog_entry
However, it would also allow:
/graemerocher/not_a_year/not_a_month/not_a_day/my_funky_blog_entry
This is problematic as it forces you to do some clever parsing in the controller code. Luckily, URL Mappings can be constrained to further validate the URL tokens:
"/$blog/$year?/$month?/$day?/$id?" {
controller = "blog"
action = "show"
constraints {
year(matches:/\d{4}/)
month(matches:/\d{2}/)
day(matches:/\d{2}/)
}
}In this case the constraints ensure that the
year,
month and
day parameters match a particular valid pattern thus relieving you of that burden later on.
URL Mappings also support named mappings. Simply put, named mappings are mappings
which have a name associated with them. The name may be used to refer to a
specific mapping when links are being generated.
The syntax for defining a named mapping is as follows:
static mappings = {
name <mapping name>: <url pattern> {
// …
}
}An example:
static mappings = {
name personList: "/showPeople" {
controller = 'person'
action = 'list'
}
name accountDetails: "/details/$acctNumber" {
controller = 'product'
action = 'accountDetails'
}
}The mapping may be referenced in a link tag in a GSP.
<g:link mapping="personList">List People</g:link>
That would result in:
<a href="/showPeople">List People</a>
Parameters may be specified using the params attribute.
<g:link mapping="accountDetails" params="[acctNumber:'8675309']">Show Account</g:link>
That would result in:
<a href="/details/8675309">Show Account</a>
Alternatively you may reference a named mapping using the link namespace.
<link:personList>List People</link:personList>
That would result in:
<a href="/showPeople">List People</a>
The link namespace approach allows parameters to be specified as attributes.
<link:accountDetails acctNumber="8675309">Show Account</link:accountDetails>
That would result in:
<a href="/details/8675309">Show Account</a>
Overview
Grails supports the creation of web flows built on the
Spring Web Flow project. A web flow is a conversation that spans multiple requests and retains state for the scope of the flow. A web flow also has a defined start and end state.
Web flows don't require an HTTP session, but instead store their state in a serialized form, which is then restored using a flow execution key that Grails passes around as a request parameter. This makes flows far more scalable than other forms of stateful application that use the HttpSession and its inherit memory and clustering concerns.
Web flow is essentially an advanced state machine that manages the "flow" of execution from one state to the next. Since the state is managed for you, you don't have to be concerned with ensuring that users enter an action in the middle of some multi step flow, as web flow manages that for you. This makes web flow perfect for use cases such as shopping carts, hotel booking and any application that has multi page work flows.
Creating a Flow
To create a flow create a regular Grails controller and then add an action that ends with the convention
Flow. For example:
class BookController {
def index = {
redirect(action:"shoppingCart")
}
def shoppingCartFlow = {
…
}
}Notice when redirecting or referring to the flow as an action we omit the
Flow suffix. In other words the name of the action of the above flow is
shoppingCart.
As mentioned before a flow has a defined start and end state. A start state is the state which is entered when a user first initiates a conversation (or flow). The start state of A Grails flow is the first method call that takes a block. For example:
class BookController {
…
def shoppingCartFlow = {
showCart {
on("checkout").to "enterPersonalDetails"
on("continueShopping").to "displayCatalogue"
}
…
displayCatalogue {
redirect(controller:"catalogue", action:"show")
}
displayInvoice()
}
}Here the
showCart node is the start state of the flow. Since the showCart state doesn't define an action or redirect it is assumed be a
view state that, by convention, refers to the view
grails-app/views/book/shoppingCart/showCart.gsp.
Notice that unlike regular controller actions, the views are stored within a directory that matches the name of the flow:
grails-app/views/book/shoppingCart.
The
shoppingCart flow also has two possible end states. The first is
displayCatalogue which performs an external redirect to another controller and action, thus exiting the flow. The second is
displayInvoice which is an end state as it has no events at all and will simply render a view called
grails-app/views/book/shoppingCart/displayInvoice.gsp whilst ending the flow at the same time.
Once a flow has ended it can only be resumed from the start state, in this case
showCart, and not from any other state.
View states
A view state is a one that doesn't define an
action or a
redirect. So for example the below is a view state:
enterPersonalDetails {
on("submit").to "enterShipping"
on("return").to "showCart"
}It will look for a view called
grails-app/views/book/shoppingCart/enterPersonalDetails.gsp by default. Note that the
enterPersonalDetails state defines two events:
submit and
return. The view is responsible for
triggering these events. If you want to change the view to be rendered you can do so with the render method:
enterPersonalDetails {
render(view:"enterDetailsView")
on("submit").to "enterShipping"
on("return").to "showCart"
}Now it will look for
grails-app/views/book/shoppingCart/enterDetailsView.gsp. If you want to use a shared view, start with a / in view argument:
enterPersonalDetails {
render(view:"/shared/enterDetailsView")
on("submit").to "enterShipping"
on("return").to "showCart"
}Now it will look for
grails-app/views/shared/enterDetailsView.gsp
Action States
An action state is a state that executes code but does not render any view. The result of the action is used to dictate flow transition. To create an action state you need to define an action to to be executed. This is done by calling the
action method and passing it a block of code to be executed:
listBooks {
action {
[ bookList:Book.list() ]
}
on("success").to "showCatalogue"
on(Exception).to "handleError"
}As you can see an action looks very similar to a controller action and in fact you can re-use controller actions if you want. If the action successfully returns with no errors the
success event will be triggered. In this case since we return a map, this is regarded as the "model" and is automatically placed in
flow scope.
In addition, in the above example we also use an exception handler to deal with errors on the line:
on(Exception).to "handleError"
What this does is make the flow transition to a state called
handleError in the case of an exception.
You can write more complex actions that interact with the flow request context:
processPurchaseOrder {
action {
def a = flow.address
def p = flow.person
def pd = flow.paymentDetails
def cartItems = flow.cartItems
flow.clear() def o = new Order(person:p, shippingAddress:a, paymentDetails:pd)
o.invoiceNumber = new Random().nextInt(9999999)
cartItems.each { o.addToItems(it) }
o.save()
[order:o]
}
on("error").to "confirmPurchase"
on(Exception).to "confirmPurchase"
on("success").to "displayInvoice"
}Here is a more complex action that gathers all the information accumulated from the flow scope and creates an
Order object. It then returns the order as the model. The important thing to note here is the interaction with the request context and "flow scope".
Transition Actions
Another form of action is what is known as a
transition action. A transition action is executed directly prior to state transition once an
event has been triggered. A trivial example of a transition action can be seen below:
enterPersonalDetails {
on("submit") {
log.trace "Going to enter shipping"
}.to "enterShipping"
on("return").to "showCart"
}Notice how we pass a block of the code to
submit event that simply logs the transition. Transition states are extremely useful for
data binding and validation, which is covered in a later section.
In order to
transition execution of a flow from one state to the next you need some way of trigger an
event that indicates what the flow should do next. Events can be triggered from either view states or action states.
Triggering Events from a View State
As discussed previously the start state of the flow in a previous code listing deals with two possible events. A
checkout event and a
continueShopping event:
def shoppingCartFlow = {
showCart {
on("checkout").to "enterPersonalDetails"
on("continueShopping").to "displayCatalogue"
}
…
}Since the
showCart event is a view state it will render the view
grails-app/book/shoppingCart/showCart.gsp. Within this view you need to have components that trigger flow execution. On a form this can be done use the
submitButton tag:
<g:form action="shoppingCart">
<g:submitButton name="continueShopping" value="Continue Shopping"></g:submitButton>
<g:submitButton name="checkout" value="Checkout"></g:submitButton>
</g:form>The form must submit back to the
shoppingCart flow. The name attribute of each
submitButton tag signals which event will be triggered. If you don't have a form you can also trigger an event with the
link tag as follows:
<g:link action="shoppingCart" event="checkout" />
Triggering Events from an Action
To trigger an event from an
action you need to invoke a method. For example there is the built in
error() and
success() methods. The example below triggers the
error() event on validation failure in a transition action:
enterPersonalDetails {
on("submit") {
def p = new Person(params)
flow.person = p
if(!p.validate())return error()
}.to "enterShipping"
on("return").to "showCart"
}In this case because of the error the transition action will make the flow go back to the
enterPersonalDetails state.
With an action state you can also trigger events to redirect flow:
shippingNeeded {
action {
if(params.shippingRequired) yes()
else no()
}
on("yes").to "enterShipping"
on("no").to "enterPayment"
}Scope Basics
You'll notice from previous examples that we used a special object called
flow to store objects within "flow scope". Grails flows have 5 different scopes you can utilize:
request - Stores an object for the scope of the current requestflash - Stores the object for the current and next request onlyflow - Stores objects for the scope of the flow, removing them when the flow reaches an end stateconversation - Stores objects for the scope of the conversation including the root flow and nested subflowssession - Stores objects inside the users session
Grails service classes can be automatically scoped to a web flow scope. See the documentation on Services for more information.
Also returning a model map from an action will automatically result in the model being placed in flow scope. For example, using a transition action, you can place objects within
flow scope as follows:
enterPersonalDetails {
on("submit") {
[person:new Person(params)]
}.to "enterShipping"
on("return").to "showCart"
}Be aware that a new request is always created for each state, so an object placed in request scope in an action state (for example) will not be available in a subsequent view state. Use one of the other scopes to pass objects from one state to another. Also note that Web Flow:
- Moves objects from flash scope to request scope upon transition between states;
- Merges objects from the flow and conversation scopes into the view model before rendering (so you shouldn't include a scope prefix when referencing these objects within a view, e.g. GSP pages).
Flow Scopes and Serialization
When placing objects in
flash,
flow or
conversation scope they must implement
java.io.Serializable otherwise you will get an error. This has an impact on
domain classes in that domain classes are typically placed within a scope so that they can be rendered in a view. For example consider the following domain class:
class Book {
String title
}In order to place an instance of the
Book class in a flow scope you will need to modify it as follows:
class Book implements Serializable {
String title
}This also impacts associations and closures you declare within a domain class. For example consider this:
class Book implements Serializable {
String title
Author author
}Here if the
Author association is not
Serializable you will also get an error. This also impacts closures used in
GORM events such as
onLoad,
onSave and so on. The following domain class will cause an error if an instance is placed in a flow scope:
class Book implements Serializable {
String title
def onLoad = {
println "I'm loading"
}
}The reason is that the assigned block on the
onLoad event cannot be serialized. To get around this you should declare all events as
transient:
class Book implements Serializable {
String title
transient onLoad = {
println "I'm loading"
}
}In the section on
start and end states, the start state in the first example triggered a transition to the
enterPersonalDetails state. This state renders a view and waits for the user to enter the required information:
enterPersonalDetails {
on("submit").to "enterShipping"
on("return").to "showCart"
}The view contains a form with two submit buttons that either trigger the submit event or the return event:
<g:form action="shoppingCart">
<g:submitButton name="submit" value="Continue"></g:submitButton>
<g:submitButton name="return" value="Back"></g:submitButton>
</g:form>However, what about the capturing the information submitted by the form? To to capture the form info we can use a flow transition action:
enterPersonalDetails {
on("submit") {
flow.person = new Person(params)
!flow.person.validate() ? error() : success()
}.to "enterShipping"
on("return").to "showCart"
}Notice how we perform data binding from request parameters and place the
Person instance within
flow scope. Also interesting is that we perform
validation and invoke the
error() method if validation fails. This signals to the flow that the transition should halt and return to the
enterPersonalDetails view so valid entries can be entered by the user, otherwise the transition should continue and go to the
enterShipping state.
Like regular actions, flow actions also support the notion of
Command Objects by defining the first argument of the closure:
enterPersonalDetails {
on("submit") { PersonDetailsCommand cmd ->
flow.personDetails = cmd
!flow.personDetails.validate() ? error() : success()
}.to "enterShipping"
on("return").to "showCart"
}Grails' Web Flow integration also supports subflows. A subflow is like a flow within a flow. For example take this search flow:
def searchFlow = {
displaySearchForm {
on("submit").to "executeSearch"
}
executeSearch {
action {
[results:searchService.executeSearch(params.q)]
}
on("success").to "displayResults"
on("error").to "displaySearchForm"
}
displayResults {
on("searchDeeper").to "extendedSearch"
on("searchAgain").to "displaySearchForm"
}
extendedSearch {
subflow(extendedSearchFlow) // <--- extended search subflow
on("moreResults").to "displayMoreResults"
on("noResults").to "displayNoMoreResults"
}
displayMoreResults()
displayNoMoreResults()
}It references a subflow in the
extendedSearch state. The subflow is another flow entirely:
def extendedSearchFlow = {
startExtendedSearch {
on("findMore").to "searchMore"
on("searchAgain").to "noResults"
}
searchMore {
action {
def results = searchService.deepSearch(ctx.conversation.query)
if(!results)return error()
conversation.extendedResults = results
}
on("success").to "moreResults"
on("error").to "noResults"
}
moreResults()
noResults()
}Notice how it places the
extendedResults in conversation scope. This scope differs to flow scope as it allows you to share state that spans the whole conversation not just the flow. Also notice that the end state (either
moreResults or
noResults of the subflow triggers the events in the main flow:
extendedSearch {
subflow(extendedSearchFlow) // <--- extended search subflow
on("moreResults").to "displayMoreResults"
on("noResults").to "displayNoMoreResults"
}Although Grails
controllers support fine grained interceptors, these are only really useful when applied to a few controllers and become difficult to manage with larger applications. Filters on the other hand can be applied across a whole group of controllers, a URI space or a to a specific action. Filters are far easier to plug-in and maintain completely separately to your main controller logic and are useful for all sorts of cross cutting concerns such as security, logging, and so on.
To create a filter create a class that ends with the convention
Filters in the
grails-app/conf directory. Within this class define a code block called
filters that contains the filter definitions:
class ExampleFilters {
def filters = {
// your filters here
}
}Each filter you define within the
filters block has a name and a scope. The name is the method name and the scope is defined using named arguments. For example if you need to define a filter that applies to all controllers and all actions you can use wildcards:
sampleFilter(controller:'*', action:'*') {
// interceptor definitions
}The scope of the filter can be one of the following things:
- A controller and/or action name pairing with optional wildcards
- A URI, with Ant path matching syntax
Filter rule attributes:
controller - controller matching pattern, by default * is replaced with .* and a regex is compiledaction - action matching pattern, by default * is replaced with .* and a regex is compiledregex (true/false) - use regex syntax (don't replace '*' with '.*')uri - a uri to match, expressed with as Ant style path (e.g. /book/**)find (true/false) - rule matches with partial match (see java.util.regex.Matcher.find())invert (true/false) - invert the rule (NOT rule)
Some examples of filters include:
- All controllers and actions
all(controller:'*', action:'*') {}
- Only for the
BookController
justBook(controller:'book', action:'*') {}
- All controllers except the
BookController
notBook(controller:'book', invert:true) {}
- All actions containing 'save' in the action name
saveInActionName(action:'save', find:true) {}someURIs(uri:'/book/**') {}In addition, the order in which you define the filters dictates the order in which they are executed.
Within the body of the filter you can then define one of the following interceptor types for the filter:
before - Executed before the action. Can return false to indicate all future filters and the action should not executeafter - Executed after an action. Takes a first argument as the view modelafterView - Executed after view rendering
For example to fulfill the common authentication use case you could define a filter as follows:
class SecurityFilters {
def filters = {
loginCheck(controller:'*', action:'*') {
before = {
if(!session.user && !actionName.equals('login')) {
redirect(action:'login')
return false
}
} }
}
}
Here the
loginCheck filter uses a
before interceptor to execute a block of code that checks if a user is in the session and if not redirects to the login action. Note how returning false ensure that the action itself is not executed.
Filters support all the common properties available to
controllers and
tag libraries, plus the application context:
However, filters only support a subset of the methods available to controllers and tag libraries. These include:
- redirect - For redirects to other controllers and actions
- render - For rendering custom responses
Ajax stands for Asynchronous Javascript and XML and is the driving force behind the shift to richer web applications. These types of applications in general are better suited to agile, dynamic frameworks written in languages like
Ruby and
Groovy Grails provides support for building Ajax applications through its Ajax tag library for a full list of these see the Tag Library Reference.
By default Grails ships with the
Prototype library, but through the
Plug-in system provides support for other frameworks such as
Dojo Yahoo UI and the
Google Web ToolkitThis section covers Grails' support for Prototype. To get started you need to add this line to the
<head> tag of your page:
<g:javascript library="prototype" />
This uses the
javascript tag to automatically place the correct references in place for Prototype. If you require
Scriptaculous too you can do the following instead:
<g:javascript library="scriptaculous" />
This works because of Grails' support for adaptive tag libraries. Thanks to Grails' plugin system there is support for a number of different Ajax libraries including (but not limited to):
- prototype
- dojo
- yui
- mootools
Remote content can be loaded in a number of ways, the most commons way is through the
remoteLink tag. This tag allows the creation of HTML anchor tags that perform an asynchronous request and optionally set the response in an element. The simplest way to create a remote link is as follows:
<g:remoteLink action="delete" id="1">Delete Book</g:remoteLink>
The above link sends an asynchronous request to the
delete action of the current controller with an id of
1.
This is great, but usually you would want to provide some kind of feedback to the user as to what has happened:
def delete = {
def b = Book.get( params.id )
b.delete()
render "Book ${b.id} was deleted"
}GSP code:
<div id="message"></div>
<g:remoteLink action="delete" id="1" update="message">Delete Book</g:remoteLink>
The above example will call the action and set the contents of the
message div to the response in this case
"Book 1 was deleted". This is done by the
update attribute on the tag, which can also take a map to indicate what should be updated on failure:
<div id="message"></div>
<div id="error"></div>
<g:remoteLink action="delete" id="1"
update="[success:'message',failure:'error']">Delete Book</g:remoteLink>Here the
error div will be updated if the request failed.
An HTML form can also be submitted asynchronously in one of two ways. Firstly using the
formRemote tag which expects similar attributes to those for the
remoteLink tag:
<g:formRemote url="[controller:'book',action:'delete']" update="[success:'message',failure:'error']">
<input type="hidden" name="id" value="1" />
<input type="submit" value="Delete Book!" />
</g:formRemote >Or alternatively you can use the
submitToRemote tag to create a submit button. This allows some buttons to submit remotely and some not depending on the action:
<form action="delete">
<input type="hidden" name="id" value="1" />
<g:submitToRemote action="delete" update="[success:'message',failure:'error']" />
</form>Specific javascript can be called if certain events occur, all the events start with the "on" prefix and allow you to give feedback to the user where appropriate, or take other action:
<g:remoteLink action="show"
id="1"
update="success"
onLoading="showProgress()"
onComplete="hideProgress()">Show Book 1</g:remoteLink>The above code will execute the "showProgress()" function which may show a progress bar or whatever is appropriate. Other events include:
onSuccess - The javascript function to call if successfulonFailure - The javascript function to call if the call failedon_ERROR_CODE - The javascript function to call to handle specified error codes (eg on404="alert('not found!')")onUninitialized - The javascript function to call the a ajax engine failed to initialiseonLoading - The javascript function to call when the remote function is loading the responseonLoaded - The javascript function to call when the remote function is completed loading the responseonComplete - The javascript function to call when the remote function is complete, including any updates
If you need a reference to the
XmlHttpRequest object you can use the implicit event parameter
e to obtain it:
<g:javascript>
function fireMe(e) {
alert("XmlHttpRequest = " + e)
}
}
</g:javascript>
<g:remoteLink action="example"
update="success"
onSuccess="fireMe(e)">Ajax Link</g:remoteLink>Grails features an external plug-in to add
Dojo support to Grails. To install the plug-in type the following command from the root of your project in a terminal window:
grails install-plugin dojo
This will download the current supported version of Dojo and install it into your Grails project. With that done you can add the following reference to the top of your page:
<g:javascript library="dojo" />
Now all of Grails tags such as
remoteLink,
formRemote and
submitToRemote work with Dojo remoting.
Grails also features support for the
Google Web Toolkit through a plug-in comprehensive
documentation for can be found on the Grails wiki.
Although Ajax features the X for XML there are a number of different ways to implement Ajax which are typically broken down into:
- Content Centric Ajax - Where you merely use the HTML result of a remote call to update the page
- Data Centric Ajax - Where you actually send an XML or JSON response from the server and programmatically update the page
- Script Centric Ajax - Where the server sends down a stream of Javascript to be evaluated on the fly
Most of the examples in the
Ajax section cover Content Centric Ajax where you are updating the page, but you may also want to use Data Centric or Script Centric. This guide covers the different styles of Ajax.
Content Centric Ajax
Just to re-cap, content centric Ajax involves sending some HTML back from the server and is typically done by rendering a template with the
render method:
def showBook = {
def b = Book.get(params.id) render(template:"bookTemplate", model:[book:b])
}Calling this on the client involves using the
remoteLink tag:
<g:remoteLink action="showBook" id="${book.id}" update="book${book.id}">Update Book</g:remoteLink>
<div id="book${book.id}">
</div>Data Centric Ajax with JSON
Data Centric Ajax typically involves evaluating the response on the client and updating programmatically. For a JSON response with Grails you would typically use Grails'
JSON marshaling capability:
import grails.converters.*def showBook = {
def b = Book.get(params.id) render b as JSON
}And then on the client parse the incoming JSON request using an Ajax event handler:
<g:javascript>
function updateBook(e) {
var book = eval("("+e.responseText+")") // evaluate the JSON
$("book"+book.id+"_title").innerHTML = book.title
}
<g:javascript>
<g:remoteLink action="test" update="foo" onSuccess="updateBook(e)">Update Book</g:remoteLink>
<g:set var="bookId">book${book.id}</g:set>
<div id="${bookId}">
<div id="${bookId}_title">The Stand</div>
</div>Data Centric Ajax with XML
On the server side using XML is equally trivial:
import grails.converters.*def showBook = {
def b = Book.get(params.id) render b as XML
}However, since DOM is involved the client gets more complicated:
<g:javascript>
function updateBook(e) {
var xml = e.responseXML
var id = xml.getElementsByTagName("book").getAttribute("id")
$("book"+id+"_title")=xml.getElementsByTagName("title")[0].textContent
}
<g:javascript>
<g:remoteLink action="test" update="foo" onSuccess="updateBook(e)">Update Book</g:remoteLink>
<g:set var="bookId">book${book.id}</g:set>
<div id="${bookId}">
<div id="${bookId}_title">The Stand</div>
</div>Script Centric Ajax with JavaScript
Script centric Ajax involves actually sending Javascript back that gets evaluated on the client. An example of this can be seen below:
def showBook = {
def b = Book.get(params.id) response.contentType = "text/javascript"
String title = b.title.encodeAsJavascript()
render "$('book${b.id}_title')='${title}'"
}The important thing to remember is to set the
contentType to
text/javascript. If you are using Prototype on the client the returned Javascript will automatically be evaluated due to this
contentType setting.
Obviously in this case it is critical that you have an agreed client-side API as you don't want changes on the client breaking the server. This is one of the reasons Rails has something like RJS. Although Grails does not currently have a feature such as RJS there is a
Dynamic JavaScript Plug-in that offers similar capabilities.
Grails has built in support for
Content negotiation using either the HTTP
Accept header, an explicit format request parameter or the extension of a mapped URI.
Configuring Mime Types
Before you can start dealing with content negotiation you need to tell Grails what content types you wish to support. By default Grails comes configured with a number of different content types within
grails-app/conf/Config.groovy using the
grails.mime.types setting:
grails.mime.types = [ xml: ['text/xml', 'application/xml'],
text: 'text-plain',
js: 'text/javascript',
rss: 'application/rss+xml',
atom: 'application/atom+xml',
css: 'text/css',
cvs: 'text/csv',
all: '*/*',
json: 'text/json',
html: ['text/html','application/xhtml+xml']
]The above bit of configuration allows Grails to detect to format of a request containing either the 'text/xml' or 'application/xml' media types as simply 'xml'. You can add your own types by simply adding new entries into the map.
Content Negotiation using the Accept header
Every incoming HTTP request has a special
Accept header that defines what media types (or mime types) a client can "accept". In older browsers this is typically:
Which simply means anything. However, on newer browser something all together more useful is sent such as (an example of a Firefox
Accept header):
text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Grails parses this incoming format and adds a
property to the
request object that outlines the preferred request format. For the above example the following assertion would pass:
assert 'html' == request.format
Why? The
text/html media type has the highest "quality" rating of 0.9, therefore is the highest priority. If you have an older browser as mentioned previously the result is slightly different:
assert 'all' == request.format
In this case 'all' possible formats are accepted by the client. To deal with different kinds of requests from
Controllers you can use the
withFormat method that acts as kind of a switch statement:
import grails.converters.*class BookController {
def books
def list = {
this.books = Book.list()
withFormat {
html bookList:books
js { render "alert('hello')" }
xml { render books as XML }
}
}
}What happens here is that if the preferred format is
html then Grails will execute the
html() call only. What this is does is make Grails look for a view called either
grails-app/views/books/list.html.gsp or
grails-app/views/books/list.gsp. If the format is
xml then the closure will be invoked and an XML response rendered.
How do we handle the "all" format? Simply order the content-types within your
withFormat block so that whichever one you want executed comes first. So in the above example, "all" will trigger the
html handler.
When using withFormat make sure it is the last call in your controller action as the return value of the withFormat method is used by the action to dictate what happens next.
Content Negotiation with the format Request Parameter
If fiddling with request headers if not your favorite activity you can override the format used by specifying a
format request parameter:
You can also define this parameter in the
URL Mappings definition:
"/book/list"(controller:"book", action:"list") {
format = "xml"
}Content Negotiation with URI Extensions
Grails also supports content negotiation via URI extensions. For example given the following URI:
Grails will shave off the extension and map it to
/book/list instead whilst simultaneously setting the content format to
xml based on this extension. This behaviour is enabled by default, so if you wish to turn it off, you must set the
grails.mime.file.extensions property in
grails-app/conf/Config.groovy to
false:
grails.mime.file.extensions = false
Testing Content Negotiation
To test content negotiation in an integration test (see the section on
Testing) you can either manipulate the incoming request headers:
void testJavascriptOutput() {
def controller = new TestController()
controller.request.addHeader "Accept", "text/javascript, text/html, application/xml, text/xml, */*" controller.testAction()
assertEquals "alert('hello')", controller.response.contentAsString
}Or you can set the format parameter to achieve a similar effect:
void testJavascriptOutput() {
def controller = new TestController()
controller.params.format = 'js' controller.testAction()
assertEquals "alert('hello')", controller.response.contentAsString
}Grails validation capability is built on
Spring's Validator API and data binding capabilities. However Grails takes this further and provides a unified way to define validation "constraints" with its constraints mechanism.
Constraints in Grails are a way to declaratively specify validation rules. Most commonly they are applied to
domain classes, however
URL Mappings and
Command Objects also support constraints.
Within a domain class a
constraints are defined with the constraints property that is assigned a code block:
class User {
String login
String password
String email
Integer age static constraints = {
…
}
}You then use method calls that match the property name for which the constraint applies in combination with named parameters to specify constraints:
class User {
... static constraints = {
login(size:5..15, blank:false, unique:true)
password(size:5..15, blank:false)
email(email:true, blank:false)
age(min:18, nullable:false)
}
}In this example we've declared that the
login property must be between 5 and 15 characters long, it cannot be blank and must be unique. We've all applied other constraints to the
password,
email and
age properties.
A complete reference for the available constraints can be found in the left navigation bar (if you have frames enabled) under the Constraints heading.
Validation Basics
To validate a domain class you can call the
validate method on any instance:
def user = new User(params)if(user.validate()) {
// do something with user
}
else {
user.errors.allErrors.each {
println it
}
}The
errors property on domain classes is an instance of the Spring
Errors interface. The
Errors interface provides methods to navigate the validation errors and also retrieve the original values.
Validation Phases
Within Grails there are essentially 2 phases of validation, the first phase is
data binding which occurs when you bind request parameters onto an instance such as:
def user = new User(params)
At this point you may already have errors in the
errors property due to type conversion (such as converting Strings to Dates). You can check these and obtain the original input value using the
Errors API:
if(user.hasErrors()) {
if(user.errors.hasFieldErrors("login")) {
println user.errors.getFieldError("login").rejectedValue
}
}The second phase of validation happens when you call
validate or
save. This is when Grails will validate the bound values againts the
constraints you defined. For example, by default the persistent
save method calls
validate before executing hence allowing you to write code like:
if(user.save()) {
return user
}
else {
user.errors.allErrors.each {
println it
}
}Displaying Errors
Typically if you get a validation error you want to redirect back to the view for rendering. Once there you need some way of rendering errors. Grails supports a rich set of tags for dealing with errors. If you simply want to render the errors as a list you can use
renderErrors:
<g:renderErrors bean="${user}" />If you need more control you can use
hasErrors and
eachError:
<g:hasErrors bean="${user}">
<ul>
<g:eachError var="err" bean="${user}">
<li>${err}</li>
</g:eachError>
</ul>
</g:hasErrors>Highlighting Errors
It is often useful to highlight using a red box or some indicator when a field has been incorrectly input. This can also be done with the
hasErrors by invoking it as a method. For example:
<div class='value ${hasErrors(bean:user,field:'login','errors')}'>
<input type="text" name="login" value="${fieldValue(bean:user,field:'login')}"/>
</div>What this code does is check if the
login field of the
user bean has any errors and if it does adds an
errors CSS class to the
div thus allowing you to use CSS rules to highlight the
div.
Retrieving Input Values
Each error is actually an instance of the
FieldError class in Spring, which retains the original input value within it. This is useful as you can use the error object to restore the value input by the user using the
fieldValue tag:
<input type="text" name="login" value="${fieldValue(bean:user,field:'login')}"/>This code will look if there is an existing
FieldError in the
User bean and if there is obtain the originally input value for the
login field.
Another important thing to note about errors in Grails is that the messages that the errors display are not hard coded anywhere. The
FieldError class in Spring essentially resolves messages from message bundles using Grails'
i18n support.
Constraints and Message Codes
The codes themselves are dictated by a convention. For example consider the constraints we looked at earlier:
package com.mycompany.myappclass User {
... static constraints = {
login(size:5..15, blank:false, unique:true)
password(size:5..15, blank:false)
email(email:true, blank:false)
age(min:18, nullable:false)
}
}If the
blank constraint was violated Grails will, by convention, look for a message code in the form:
[Class Name].[Property Name].[Constraint Code]
In the case of the
blank constraint this would be
user.login.blank so you would need a message such as the following in your
grails-app/i18n/messages.properties file:
user.login.blank=Your login name must be specified!
The class name is looked for both with and without a package, with the packaged version taking precedence. So for example, com.mycompany.myapp.User.login.blank will be used before user.login.blank. This allows for cases where you domain class encounters message code clashes with plugins.
For a reference on what codes are for which constraints refer to the reference guide for each constraint.
Displaying Messages
The
renderErrors tag will automatically deal with looking up messages for you using the
message tag. However, if you need more control of rendering you will need to do this yourself:
<g:hasErrors bean="${user}">
<ul>
<g:eachError var="err" bean="${user}">
<li><g:message error="${err}" /></li>
</g:eachError>
</ul>
</g:hasErrors>In this example within the body of the
eachError tag we use the
message tag in combination with its
error argument to read the message for the given error.
Domain classes and
command objects support validation by default. Other classes may be made validateable by defining the static constraints property in the class (as described above) and then telling the framework about them. It is important that the application register the validateable classes with the framework. Simply defining the constraints property is not sufficient.
The Validateable Annotation
Classes which define the static constraints property and are marked with the @Validateable annotation may be made validateable by the framework. Consider this example:
// src/groovy/com/mycompany/myapp/User.groovy
package com.mycompany.myappimport org.codehaus.groovy.grails.validation.Validateable@Validateable
class User {
... static constraints = {
login(size:5..15, blank:false, unique:true)
password(size:5..15, blank:false)
email(email:true, blank:false)
age(min:18, nullable:false)
}
}You need to tell the framework which packages to search for @Validateable classes by assigning a list of Strings to the grails.validateable.packages property in Config.groovy.
// grails-app/conf/Config.groovy...grails.validateable.packages = ['com.mycompany.dto', 'com.mycompany.util']...
The framework will only search those packages (and child packages of those) for classes marked with @Validateable.
Registering Validateable Classes
If a class is not marked with @Validateable, it may still be made validateable by the framework. The steps required to do this are to define the static constraints property in the class (as described above) and then telling the framework about the class by assigning a value to the grails.validateable.classes property in Config.groovy.
// grails-app/conf/Config.groovy...grails.validateable.classes = [com.mycompany.myapp.User, com.mycompany.dto.Account]...
As well as the
Web layer, Grails defines the notion of a service layer. The Grails team discourages the embedding of core application logic inside controllers, as it does not promote re-use and a clean separation of concerns.
Services in Grails are seen as the place to put the majority of the logic in your application, leaving controllers responsible for handling request flow via redirects and so on.
Creating a Service
You can create a Grails service by running the
create-service command from the root of your project in a terminal window:
grails create-service simple
The above example will create a service at the location
grails-app/services/SimpleService.groovy. A service's name ends with the convention
Service, other than that a service is a plain Groovy class:
Default Declarative Transactions
Services are typically involved with co-ordinating logic between
domain classes, and hence often involved with persistence that spans large operations. Given the nature of services they frequently require transactional behaviour. You can of course use programmatic transactions with the
withTransaction method, however this is repetitive and doesn't fully leverage the power of Spring's underlying transaction abstraction.
Services allow the enablement of transaction demarcation, which is essentially a declarative way of saying all methods within this service are to be made transactional. All services have transaction demarcation enabled by default - to disable it, simply set the
transactional property to
false:
class CountryService {
static transactional = false
}You may also set this property to
true in case the default changes in the future, or simply to make it clear that the service is intentionally transactional.
Warning: dependency injection is the only way that declarative transactions work. You will not get a transactional service if you use the new operator such as new BookService()
The result is all methods are wrapped in a transaction and automatic rollback occurs if an exception is thrown in the body of one of the methods. The propagation level of the transaction is by default set to
PROPAGATION_REQUIRED.
Custom Transaction Configuration
Grails also fully supports Spring's
Transactional annotation for cases where you need more fine-grained control over transactions at a per-method level or need specify an alternative propagation level:
import org.springframework.transaction.annotation.*class BookService { @Transactional(readOnly = true)
def listBooks() { Book.list() } @Transactional def updateBook() {
// …
}}For more information refer to the section of the Spring user guide on
Using @Transactional.
Unlike Spring you do not need any prior configuration to use Transactional, just specify the annotation as needed and Grails will pick them up automatically.
By default, access to service methods is not synchronised, so nothing prevents concurrent execution of those functions. In fact, because the service is a singleton and may be used concurrently, you should be very careful about storing state in a service. Or take the easy (and better) road and never store state in a service.
You can change this behaviour by placing a service in a particular scope. The supported scopes are:
prototype - A new service is created every time it is injected into another classrequest - A new service will be created per requestflash - A new service will be created for the current and next request onlyflow - In web flows the service will exist for the scope of the flowconversation - In web flows the service will exist for the scope of the conversation. ie a root flow and its sub flowssession - A service is created for the scope of a user sessionsingleton (default) - Only one instance of the service ever exists
If your service is flash, flow or conversation scoped it will need to implement java.io.Serializable and can only be used in the context of a Web Flow
To enable one of the scopes, add a static scope property to your class whose value is one of the above:
Dependency Injection Basics
A key aspect of Grails services is the ability to take advantage of the
Spring Framework's dependency injection capability. Grails supports "dependency injection by convention". In other words, you can use the property name representation of the class name of a service, to automatically inject them into controllers, tag libraries, and so on.
As an example, given a service called
BookService, if you place a property called
bookService within a controller as follows:
class BookController {
def bookService
…
}In this case, the Spring container will automatically inject an instance of that service based on its configured scope. All dependency injection is done by name. You can also specify the type as follows:
class AuthorService {
BookService bookService
}
NOTE: Normally the property name is generated by lower casing the first letter of the type. For example, an instance of the BookService class would map to a property named bookService.To be consistent with standard JavaBean convetions, if the first 2 letters of the class name are upper case, the property name is the same as the class name. For example, an instance of the MYhelperService class would map to a property named MYhelperService.See section 8.8 of the JavaBean specification for more information on de-capitalization rules.
Dependency Injection and Services
You can inject services in other services with the same technique. Say you had an
AuthorService that needed to use the
BookService, declaring the
AuthorService as follows would allow that:
class AuthorService {
def bookService
}Dependency Injection and Domain Classes
You can even inject services into domain classes, which can aid in the development of rich domain models:
class Book {
…
def bookService
def buyBook() {
bookService.buyBook(this)
}
}One of the powerful things about services is that since they encapsulate re-usable logic, you can use them from other classes, including Java classes. There are a couple of ways you can re-use a service from Java. The simplest way is to move your service into a package within the
grails-app/services directory. The reason this is a critical step is that it is not possible to import classes into Java from the default package (the package used when no package declaration is present). So for example the
BookService below cannot be used from Java as it stands:
class BookService {
void buyBook(Book book) {
// logic
}
}However, this can be rectified by placing this class in a package, by moving the class into a sub directory such as
grails-app/services/bookstore and then modifying the package declaration:
package bookstore
class BookService {
void buyBook(Book book) {
// logic
}
}An alternative to packages is to instead have an interface within a package that the service implements:
package bookstore;
interface BookStore {
void buyBook(Book book);
}And then the service:
class BookService implements bookstore.BookStore {
void buyBook(Book b) {
// logic
}
}This latter technique is arguably cleaner, as the Java side only has a reference to the interface and not to the implementation class. Either way, the goal of this exercise to enable Java to statically resolve the class (or interface) to use, at compile time. Now that this is done you can create a Java class within the
src/java package, and provide a setter that uses the type and the name of the bean in Spring:
package bookstore;
// note: this is Java class
public class BookConsumer {
private BookStore store; public void setBookStore(BookStore storeInstance) {
this.store = storeInstance;
}
…
}Once this is done you can configure the Java class as a Spring bean in
grails-app/conf/spring/resources.xml (For more information one this see the section on
Grails and Spring):
<bean id="bookConsumer" class="bookstore.BookConsumer">
<property name="bookStore" ref="bookService" />
</bean>
Automated testing is seen as a key part of Grails, implemented using
Groovy Tests. Hence, Grails provides many ways to making testing easier from low level unit testing to high level functional tests. This section details the different capabilities that Grails offers in terms of testing.
The first thing to be aware of is that all of the
create-* commands actually end up creating
integration tests automatically for you. For example say you run the
create-controller command as follows:
grails create-controller simple
Not only will Grails create a controller at
grails-app/controllers/SimpleController.groovy, but also an integration test at
test/integration/SimpleControllerTests.groovy. What Grails won't do however is populate the logic inside the test! That is left up to you.
As of Grails 1.2.2,the suffix of Test is also supported for test cases.
Running Tests
Test are run with the
test-app command:
The above command will produce output such as:
-------------------------------------------------------
Running Unit Tests…
Running test FooTests...FAILURE
Unit Tests Completed in 464ms …
-------------------------------------------------------Tests failed: 0 errors, 1 failures
Whilst reports will have been written out the
target/test-reports directory.
You can force a clean before running tests by passing -clean to the test-app command.
Targeting Tests
You can selectively target the test(s) to be run in different ways. To run all tests for a controller named
SimpleController you would run:
grails test-app SimpleController
This will run any tests for the class named
SimpleController. Wildcards can be used...
grails test-app *Controller
This will test all classes ending in
Controller. Package names can optionally be specified...
grails test-app some.org.*Controller
or to run all tests in a package...
grails test-app some.org.*
or to run all tests in a package including subpackages...
grails test-app some.org.**
You can also target particular test methods...
grails test-app SimpleController.testLogin
This will run the
testLogin test in the
SimpleController tests. You can specify as many patterns in combination as you like...
grails test-app some.org.* SimpleController.testLogin BookController
Targeting Test Types and/or Phases
In addition to targeting certain tests, you can also target test
types and/or
phases by using the
phase:type syntax.
Grails organises tests by phase and by type. A test phase relates to the state of the Grails application during the tests, and the type relates to the testing mechanism.Grails comes with support for 4 test phases (unit, integration, functional and other) and JUnit test types for the unit and integration phases. These test types have the same name as the phase.Testing plugins may provide new test phases or new test types for existing phases. Refer to the plugin documentation.
To execute the JUnit
integration tests you can run:
grails test-app integration:integration
Both
phase and
type are optional. Their absence acts as a wildcard. The following command will run all test types in the
unit phase:
The Grails
Spock Plugin is one plugin that adds new test types to Grails. It adds a
spock test type to the
unit,
integration and
functional phases. To run all spock tests in all phases you would run the following:
To run the all of the spock tests in the
functional phase you would run...
grails test-app functional:spock
More than one pattern can be specified...
grails test-app unit:spock integration:spock
Targeting Tests in Types and/or Phases
Test and type/phase targetting can be applied at the same time:
grails test-app integration: unit: some.org.**
This would run all tests in the
integration and
unit phases that are in the page
some.org or a subpackage of.
Unit testing are tests at the "unit" level. In other words you are testing individual methods or blocks of code without considering for surrounding infrastructure. In Grails you need to be particularity aware of the difference between unit and integration tests because in unit tests Grails
does not inject any of the dynamic methods present during integration tests and at runtime.
This makes sense if you consider that the methods injected by Grails typically communicate with the database (with GORM) or the underlying Servlet engine (with Controllers).
For example say you have service like the following in
BookController:
class MyService {
def otherService String createSomething() {
def stringId = otherService.newIdentifier()
def item = new Item(code: stringId, name: "Bangle")
item.save()
return stringId
} int countItems(String name) {
def items = Item.findAllByName(name)
return items.size()
}
}
As you can see the service takes advantage of GORM methods. So how do you go about testing the above code in a unit test? The answer can be found in Grails' testing support classes.
The Testing Framework
The core of the testing plugin is the
grails.test.GrailsUnitTestCase class. This is a sub-class of
GroovyTestCase geared towards Grails applications and their artifacts. It provides several methods for mocking particular types as well as support for general mocking a la Groovy's MockFor and StubFor classes.
Normally you might look at the
MyService example shown previously and the dependency on another service and the use of dynamic domain class methods with a bit of a groan. You can use meta-class programming and the "map as object" idiom, but these can quickly get ugly. How might we write the test with GrailsUnitTestCase ?
import grails.test.GrailsUnitTestCaseclass MyServiceTests extends GrailsUnitTestCase {
void testCreateSomething() {
// Mock the domain class.
mockDomain(Item) // Mock the "other" service.
String testId = "NH-12347686"
def otherControl = mockFor(OtherService)
otherControl.demand.newIdentifier(1..1) {-> return testId } // Initialise the service and test the target method.
def testService = new MyService()
testService.otherService = otherControl.createMock() def retval = testService.createSomething() // Check that the method returns the identifier returned by the
// mock "other" service and also that a new Item instance has
// been saved.
def testInstances = Item.list()
assertEquals testId, retval
assertEquals 1, testInstances.size()
assertTrue testInstances[0] instanceof Item
} void testCountItems() {
// Mock the domain class, this time providing a list of test
// Item instances that can be searched.
def testInstances = [ new Item(code: "NH-4273997", name: "Laptop"),
new Item(code: "EC-4395734", name: "Lamp"),
new Item(code: "TF-4927324", name: "Laptop") ]
mockDomain(Item, testInstances) // Initialise the service and test the target method. def testService = new MyService() assertEquals 2, testService.countItems("Laptop")
assertEquals 1, testService.countItems("Lamp")
assertEquals 0, testService.countItems("Chair")
}
}OK, so a fair bit of new stuff there, but once we break it down you should quickly see how easy it is to use the methods available to you. Take a look at the "testCreateSomething()" test method. The first thing you will probably notice is the
mockDomain() method, which is one of several provided by
GrailsUnitTestCase:
def testInstances = []
mockDomain(Item, testInstances)
It adds all the common domain methods (both instance and static) to the given class so that any code using it sees it as a full-blown domain class. So for example, once the
Item class has been mocked, we can safely call the
save() method on instances of it. Invoking the
save() method doesn't really save the instance to any database but it will cache the object in the testing framework so the instance will be visible to certain queries. The following code snippet demonstrates the effect of calling the
save() method.
void testSomething() {
def testInstances=[]
mockDomain(Song, testInstances)
assertEquals(0, Song.count())
new Song(name:"Supper's Ready").save()
assertEquals(1, Song.count())
}The next bit we want to look at is centered on the
mockFor method:
def otherControl = mockFor(OtherService)
otherControl.demand.newIdentifier(1..1) {-> return testId }This is analagous to the
MockFor and
StubFor classes that come with Groovy and it can be used to mock any class you want. In fact, the "demand" syntax is identical to that used by Mock/StubFor, so you should feel right at home. Of course you often need to inject a mock instance as a dependency, but that is pretty straight forward with the
createMock() method, which you simply call on the mock control as shown. For those familiar with EasyMock, the name
otherControl highlights the role of the object returned by
mockFor() - it is a control object rather than the mock itself.
The rest of the
testCreateSomething() method should be pretty familiar, particularly as you now know that the mock
save() method adds instances to
testInstances list. However, there is an important technique missing from the test method. We can determine that the mock
newIdentifier() method is called because its return value has a direct impact on the result of the
createSomething() method. But what if that weren't the case? How would we know whether it had been called or not? With Mock/StubFor the check would be performed at the end of the
use() closure, but that's not available here. Instead, you can call
verify() on the control object - in this case
otherControl. This will perform the check and throw an assertion error if it hasn't been called when it should have been.
Lastly,
testCountItems() in the example demonstrates another facet of the
mockDomain() method:
def testInstances = [ new Item(code: "NH-4273997", name: "Laptop"),
new Item(code: "EC-4395734", name: "Lamp"),
new Item(code: "TF-4927324", name: "Laptop") ]
mockDomain(Item, testInstances)
It is normally quite fiddly to mock the dynamic finders manually, and you often have to set up different data sets for each invocation. On top of that, if you decide a different finder should be used then you have to update the tests to check for the new method! Thankfully the
mockDomain() method provides a lightweight implementation of the dynamic finders backed by a list of domain instances. Simply provide the test data as the second argument of the method and the mock finders will just work.
GrailsUnitTestCase - the mock methods
You have already seen a couple of examples in the introduction of the
mock..() methods provided by the
GrailsUnitTestCase class. Here we will look at all the available methods in some detail, starting with the all-purpose
mockFor(). But before we do, there is a very important point to make: using these methods ensures that any changes you make to the given classes do not leak into other tests! This is a common and serious problem when you try to perform the mocking yourself via meta-class programming, but that headache just disappears as long as you use at least one of
mock..() methods on each class you want to mock.
mockFor(class, loose = false)
General purpose mocking that allows you to set up either strict or loose demands on a class.
This method is surprisingly intuitive to use. By default it will create a strict mock control object (one for which the order in which methods are called is important) that you can use to specify demands:
def strictControl = mockFor(MyService)
strictControl.demand.someMethod(0..2) { String arg1, int arg2 -> … }
strictControl.demand.static.aStaticMethod {-> … }Notice that you can mock static methods as well as instance ones simply by using the "static" property after "demand". You then specify the name of the method that you want to mock with an optional range as its argument. This range determines how many times you expect the method to be called, so if the number of invocations falls outside of that range (either too few or too many) then an assertion error will be thrown. If no range is specified, a default of "1..1" is assumed, i.e. that the method must be called exactly once.
The last part of a demand is a closure representing the implementation of the mock method. The closure arguments should match the number and types of the mocked method, but otherwise you are free to add whatever you want in the body.
As we mentioned before, if you want an actual mock instance of the class that you are mocking, then you need to call
mockControl.createMock(). In fact, you can call this as many times as you like to create as many mock instances as you need. And once you have executed the test method, you can call
mockControl.verify() to check whether the expected methods were actually called or not.
Lastly, the call:
def looseControl = mockFor(MyService, true)
will create a mock control object that has only loose expectations, i.e. the order that methods are invoked does not matter.
mockDomain(class, testInstances = )
Takes a class and makes mock implementations of all the domain class methods (both instance- and static-level) accessible on it.
Mocking domain classes is one of the big wins from using the testing plugin. Manually doing it is fiddly at best, so it's great that mockDomain() takes that burden off your shoulders.
In effect,
mockDomain() provides a lightweight version of domain classes in which the "database" is simply a list of domain instances held in memory. All the mocked methods (
save() ,
get() ,
findBy*() , etc.) work against that list, generally behaving as you would expect them to. In addition to that, both the mocked
save() and validate() methods will perform real validation (support for the unique constraint included!) and populate an errors object on the corresponding domain instance.
There isn't much else to say other than that the plugin does not support the mocking of criteria or HQL queries. If you use either of those, simply mock the corresponding methods manually (for example with
mockFor() ) or use an integration test with real data.
mockForConstraintsTests(class, testInstances = )
Highly specialised mocking for domain classes and command objects that allows you to check whether the constraints are behaving as you expect them to.
Do you test your domain constraints? If not, why not? If your answer is that they don't need testing, think again. Your constraints contain logic and that logic is highly susceptible to bugs - the kind of bugs that can be tricky to track down (particularly as save() doesn't throw an exception when it fails). If your answer is that it's too hard or fiddly, that is no longer an excuse. Enter the
mockForConstraintsTests() method.
This is like a much reduced version of the
mockDomain() method that simply adds a
validate() method to a given domain class. All you have to do is mock the class, create an instance with field values, and then call
validate(). You can then access the errors property on your domain instance to find out whether the validation failed or not. So if all we are doing is mocking the
validate() method, why the optional list of test instances? That is so that we can test unique constraints as you will soon see.
So, suppose we have a simple domain class like so:
class Book {
String title
String author static constraints = {
title(blank: false, unique: true)
author(blank: false, minSize: 5)
}
}Don't worry about whether the constraints are sensible or not (they're not!), they are for demonstration only. To test these constraints we can do the following:
class BookTests extends GrailsUnitTestCase {
void testConstraints() {
def existingBook = new Book(title: "Misery", author: "Stephen King")
mockForConstraintsTests(Book, [ existingBook ]) // Validation should fail if both properties are null.
def book = new Book()
assertFalse book.validate()
assertEquals "nullable", book.errors["title"]
assertEquals "nullable", book.errors["author"] // So let's demonstrate the unique and minSize constraints.
book = new Book(title: "Misery", author: "JK")
assertFalse book.validate()
assertEquals "unique", book.errors["title"]
assertEquals "minSize", book.errors["author"] // Validation should pass!
book = new Book(title: "The Shining", author: "Stephen King")
assertTrue book.validate()
}
}You can probably look at that code and work out what's happening without any further explanation. The one thing we will explain is the way the errors property is used. First, it does return a real Spring
Errors instance, so you can access all the properties and methods you would normally expect. Second, this particular
Errors object also has map/property access as shown. Simply specify the name of the field you are interested in and the map/property access will return the name of the constraint that was violated. Note that it is the constraint name , not the message code (as you might expect).
That's it for testing constraints. One final thing we would like to say is that testing the constraints in this way catches a common error: typos in the "constraints" property! It is currently one of the hardest bugs to track down normally, and yet a unit test for your constraints will highlight the problem straight away.
mockLogging(class, enableDebug = false)
Adds a mock "log" property to a class. Any messages passed to the mock logger are echoed to the console.
mockController(class)
Adds mock versions of the dynamic controller properties and methods to the given class. This is typically used in conjunction with the
ControllerUnitTestCase class.
mockTagLib(class)
Adds mock versions of the dynamic taglib properties and methods to the given class. This is typically used in conjunction with the
TagLibUnitTestCase class.
Integration tests differ from unit tests in that you have full access to the Grails environment within the test. Grails will use an in-memory HSQLDB database for integration tests and clear out all the data from the database in between each test.
Testing Controllers
To test controllers you first have to understand the Spring Mock Library
Essentially Grails automatically configures each test with a
MockHttpServletRequest,
MockHttpServletResponse, and
MockHttpSession which you can then use to perform your tests. For example consider the following controller:
class FooController { def text = {
render "bar"
} def someRedirect = {
redirect(action:"bar")
}
}The tests for this would be:
class FooControllerTests extends GroovyTestCase { void testText() {
def fc = new FooController()
fc.text()
assertEquals "bar", fc.response.contentAsString
} void testSomeRedirect() { def fc = new FooController()
fc.someRedirect()
assertEquals "/foo/bar", fc.response.redirectedUrl
}
}In the above case the response is an instance of
MockHttpServletResponse which we can use to obtain the
contentAsString (when writing to the response) or the URL redirected to for example. These mocked versions of the Servlet API are, unlike the real versions, all completely mutable and hence you can set properties on the request such as the
contextPath and so on.
Grails
does not invoke
interceptors automatically when calling actions during integration testing. You should test interceptors in isolation, and via
functional testing if necessary.
Testing Controllers with Services
If your controller references a service, you have to explicitly initialise the service from your test.
Given a controller using a service:
class FilmStarsController {
def popularityService def update = {
// do something with popularityService
}
}The test for this would be:
class FilmStarsTests extends GroovyTestCase {
def popularityService public void testInjectedServiceInController () {
def fsc = new FilmStarsController()
fsc.popularityService = popularityService
fsc.update()
}
}Testing Controller Command Objects
With command objects you just supply parameters to the request and it will automatically do the command object work for you when you call your action with no parameters:
Given a controller using a command object:
class AuthenticationController {
def signup = { SignupForm form ->
…
}
}You can then test it like this:
def controller = new AuthenticationController()
controller.params.login = "marcpalmer"
controller.params.password = "secret"
controller.params.passwordConfirm = "secret"
controller.signup()
Grails auto-magically sees your call to
signup() as a call to the action and populates the command object from the mocked request parameters. During controller testing, the
params are mutable with a mocked request supplied by Grails.
Testing Controllers and the render Method
The
render method allows you to render a custom view at any point within the body of an action. For instance, consider the example below:
def save = {
def book = Book(params)
if(book.save()) {
// handle
}
else {
render(view:"create", model:[book:book])
}
}In the above example the result of the model of the action is not available as the return value, but instead is stored within the
modelAndView property of the controller. The
modelAndView property is an instance of Spring MVC's
ModelAndView class and you can use it to the test the result of an action:
def bookController = new BookController()
bookController.save()
def model = bookController.modelAndView.model.book
Simulating Request Data
If you're testing an action that requires request data such as a REST web service you can use the Spring
MockHttpServletRequest object to do so. For example consider this action which performs data binding from an incoming request:
def create = {
[book: new Book(params['book']) ]
}If you wish the simulate the 'book' parameter as an XML request you could do something like the following:
void testCreateWithXML() {
def controller = new BookController()
controller.request.contentType = 'text/xml'
controller.request.content = '''<?xml version="1.0" encoding="ISO-8859-1"?>
<book>
<title>The Stand</title>
…
</book>
'''.getBytes() // note we need the bytes def model = controller.create()
assert model.book
assertEquals "The Stand", model.book.title
}The same can be achieved with a JSON request:
void testCreateWithJSON() {
def controller = new BookController()
controller.request.contentType = "text/json"
controller.request.content = '{"id":1,"class":"Book","title":"The Stand"}'.getBytes() def model = controller.create()
assert model.book
assertEquals "The Stand", model.book.title}
With JSON don't forget the class property to specify the name the target type to bind too. In the XML this is implicit within the name of the <book> node, but with JSON you need this property as part of the JSON packet.
For more information on the subject of REST web services see the section on
REST.
Testing Web Flows
Testing
Web Flows requires a special test harness called
grails.test.WebFlowTestCase which sub classes Spring Web Flow's
AbstractFlowExecutionTests class.
Subclasses of WebFlowTestCase must be integration tests
For example given this trivial flow:
class ExampleController {
def exampleFlow = {
start {
on("go") {
flow.hello = "world"
}.to "next"
}
next {
on("back").to "start"
on("go").to "end"
}
end()
}
}You need to tell the test harness what to use for the "flow definition". This is done via overriding the abstract
getFlow
method:
class ExampleFlowTests extends grails.test.WebFlowTestCase {
def getFlow() { new ExampleController().exampleFlow }
…
}If you need to specify the flow id you can do so by overriding the getFlowId method otherwise the default is
test:
class ExampleFlowTests extends grails.test.WebFlowTestCase {
String getFlowId() { "example" }
…
}Once this is done in your test you need to kick off the flow with the
startFlow method which returns a
ViewSelection object:
void testExampleFlow() {
def viewSelection = startFlow() assertEquals "start", viewSelection.viewName
…
}As demonstrated above you can check you're on the right state using the
viewName property of the
ViewSelection object. To trigger and event you need to use the
signalEvent method:
void testExampleFlow() {
…
viewSelection = signalEvent("go")
assertEquals "next", viewSelection.viewName
assertEquals "world", viewSelection.model.hello
}Here we have signaled to the flow to execute the event "go" this causes a transition to the "next" state. In the example a transition action placed a
hello variable into the flow scope. We can test the value of this variable by inspecting the
model property of the
ViewSelection as above.
Testing Tag Libraries
Testing tag libraries is actually pretty trivial because when a tag is invoked as a method it returns its result as a string. So for example if you have a tag library like this:
class FooTagLib {
def bar = { attrs, body ->
out << "<p>Hello World!</p>"
} def bodyTag = { attrs, body ->
out << "<${attrs.name}>"
out << body()
out << "</${attrs.name}>"
}
}The tests would look like:
class FooTagLibTests extends GroovyTestCase { void testBarTag() {
assertEquals "<p>Hello World!</p>", new FooTagLib().bar(null,null).toString()
} void testBodyTag() {
assertEquals "<p>Hello World!</p>", new FooTagLib().bodyTag(name:"p") {
"Hello World!"
}.toString()
}
}Notice that for the second example,
testBodyTag, we pass a block that returns the body of the tag. This is handy for representing the body as a String.
Testing Tag Libraries with GroovyPagesTestCase
In addition to doing simply testing of tag libraries like the above you can also use the
grails.test.GroovyPagesTestCase class to test tag libraries.
The
GroovyPagesTestCase class is a sub class of the regular
GroovyTestCase class and provides utility methods for testing the output of a GSP rendering.
GroovyPagesTestCase can only be used in an integration test.
As an example given a date formatting tag library such as the one below:
class FormatTagLib {
def dateFormat = { attrs, body ->
out << new java.text.SimpleDateFormat(attrs.format) << attrs.date
}
}This can be easily tested as follows:
class FormatTagLibTests extends GroovyPagesTestCase {
void testDateFormat() {
def template = '<g:dateFormat format="dd-MM-yyyy" date="${myDate}" />' def testDate = … // create the date
assertOutputEquals( '01-01-2008', template, [myDate:testDate] )
}
}You can also obtain the result of a GSP using the
applyTemplate method of the
GroovyPagesTestCase class:
class FormatTagLibTests extends GroovyPagesTestCase {
void testDateFormat() {
def template = '<g:dateFormat format="dd-MM-yyyy" date="${myDate}" />' def testDate = … // create the date
def result = applyTemplate( template, [myDate:testDate] ) assertEquals '01-01-2008', result
}
}Testing Domain Classes
Testing domain classes is typically a simple matter of using the
GORM API, however there are some things to be aware of. Firstly, if you are testing queries you will often need to "flush" in order to ensure the correct state has been persisted to the database. For example take the following example:
void testQuery() {
def books = [ new Book(title:"The Stand"), new Book(title:"The Shining")]
books*.save() assertEquals 2, Book.list().size()
}This test will actually fail, because calling
save does not actually persist the
Book instances when called. Calling
save merely indicates to Hibernate that at some point in the future these instances should be persisted. If you wish to commit changes immediately you need to "flush" them:
void testQuery() {
def books = [ new Book(title:"The Stand"), new Book(title:"The Shining")]
books*.save(flush:true) assertEquals 2, Book.list().size()
}In this case since we're passing the argument
flush with a value of
true the updates will be persisted immediately and hence will be available to the query later on.
Functional tests involve testing the actual running application and are often harder to automate. Grails does not ship with any functional testing support out of the box, but has support for
Canoo WebTest via a plug-in.
To get started install Web Test with the following commands:
grails install-plugin webtest
Then refer to the
reference on the wiki which explains how to go about using Web Test and Grails.
Grails supports Internationalization (i18n) out of the box through the underlying Spring MVC support for internationalization. With Grails you are able to customize the text that appears in any view based on the users Locale. To quote the javadoc for the
Locale class in Java:
A Locale object represents a specific geographical, political, or cultural region. An operation that requires a Locale to perform its task is called locale-sensitive and uses the Locale to tailor information for the user. For example, displaying a number is a locale-sensitive operation--the number should be formatted according to the customs/conventions of the user's native country, region, or culture.
A Locale is made up of a
language code and a
country code. For example "en_US" is the code for US english, whilst "en_GB" is the for British English.
Now that you have an idea of locales, to take advantage of them in Grails you have to create message bundles that contain the different languages that you wish to render. Message bundles in Grails are located inside the
grails-app/i18n directory and are simple Java properties files.
Each bundle starts with the name
messages by convention and ends with the locale. Grails ships with a bunch of built in message bundles for a whole range of languages within the
grails-app/i18n directory. For example:
messages.properties
messages_de.properties
messages_es.properties
etc.
By default Grails will look in
messages.properties for messages, unless the user has specified a custom locale. You can create your own message bundle by simply creating a new properties file that ends with the locale you are interested. For example
messages_en_GB.properties for British English.
By default the user locale is detected from the incoming
Accept-Language header. However, you can provide users the capability to switch locales by simply passing a parameter called
lang to Grails as a request parameter:
Grails will automatically switch the user locale and store it in a cookie so subsequent requests will have the new header.
Reading Messages in the View
The most common place that you need messages is inside the view. To read messages from the view just use the
message tag:
<g:message code="my.localized.content" />
As long as you have a key in your
messages.properties (with appropriate locale suffix) such as the one below then Grails will look-up the message:
my.localized.content=Hola, Me llamo John. Hoy es domingo.
Note that sometimes you may need to pass arguments to the message. This is also possible with the
message tag:
<g:message code="my.localized.content" args="${ ['Juan', 'lunes'] }" />And then use positional parameters in the message:
my.localized.content=Hola, Me llamo {0}. Hoy es {1}.Reading Messages in Controllers and Tag Libraries
Since you can invoke tags as methods from controllers it is also trivial to read messages within in a controller:
def show = {
def msg = message(code:"my.localized.content", args:['Juan', 'lunes'])
}The same technique can be used on
tag libraries, but note if your tag library has a different
namespace then you will need to
g. prefix:
def myTag = { attrs, body ->
def msg = g.message(code:"my.localized.content", args:['Juan', 'lunes'])
}Grails does not ship with i18n aware
scaffolding templates to generate the controller and views. However, i18n aware templates are available via the i18n templates plugin. The templates are identical to the default scaffolding templates, except that they are i18n aware using the
message tag for labels, buttons etc.
To get started install the i18n templates with the following command:
grails install-plugin i18n-templates
Then refer to the
reference on the wiki which explains how to use the i18n templates.
Grails is no more or less secure than Java Servlets. However, Java servlets (and hence Grails) are extremely secure and largely immune to common buffer overrun and malformed URL exploits due to the nature of the Java Virtual Machine underpinning the code.
Web security problems typically occur due to developer naivety or mistakes, and there is a little Grails can do to avoid common mistakes and make writing secure applications easier to write.
What Grails Automatically Does
Grails has a few built in safety mechanisms by default.
- All standard database access via GORM domain objects is automatically SQL escaped to prevent SQL injection attacks
- The default scaffolding templates HTML escape all data fields when displayed
- Grails link creating tags (link, form, createLink, createLinkTo and others) all use appropriate escaping mechanisms to prevent code injection
- Grails provides codecs to allow you to trivially escape data when rendered as HTML, JavaScript and URLs to prevent injection attacks here.
SQL injection
Hibernate, which is the technology underlying GORM domain classes, automatically escapes data when committing to database so this is not an issue. However it is still possible to write bad dynamic HQL code that uses unchecked request parameters. For example doing the following is vulnerable to HQL injection attacks:
def vulnerable = {
def books = Book.find("from Book as b where b.title ='" + params.title + "'")
}Do
not do this. If you need to pass in parameters use named or positional parameters instead:
def safe = {
def books = Book.find("from Book as b where b.title =?", [params.title])
}Phishing
This really a public relations issue in terms of avoiding hijacking of your branding and a declared communication policy with your customers. Customers need to know how to identify bonafide emails received.
XSS - cross-site scripting injection
It is important that your application verifies as much as possible that incoming requests were originated from your application and not from another site. Ticketing and page flow systems can help this and Grails' support for
Spring Web Flow includes security like this by default.
It is also important to ensure that all data values rendered into views are escaped correctly. For example when rendering to HTML or XHTML you must call
encodeAsHTML on every object to ensure that people cannot maliciously inject JavaScript or other HTML into data or tags viewed by others. Grails supplies several
Dynamic Encoding Methods for this purpose and if your output escaping format is not supported you can easily write your own codec.
You must also avoid the use of request parameters or data fields for determining the next URL to redirect the user to. If you use a
successURL parameter for example to determine where to redirect a user to after a successful login, attackers can imitate your login procedure using your own site, and then redirect the user back to their own site once logged in, potentially allowing JS code to then exploit the logged-in account on the site.
HTML/URL injection
This is where bad data is supplied such that when it is later used to create a link in a page, clicking it will not cause the expected behaviour, and may redirect to another site or alter request parameters.
HTML/URL injection is easily handled with the
codecs supplied by Grails, and the tag libraries supplied by Grails all use
encodeAsURL where appropriate. If you create your own tags that generate URLs you will need to be mindful of doing this too.
Denial of service
Load balancers and other appliances are more likely to be useful here, but there are also issues relating to excessive queries for example where a link is created by an attacker to set the maximum value of a result set so that a query could exceed the memory limits of the server or slow the system down. The solution here is to always sanitize request parameters before passing them to dynamic finders or other GORM query methods:
def safeMax = Math.max(params.max?.toInteger(), 100) // never let more than 100 results be returned
return Book.list(max:safeMax)
Guessable IDs
Many applications use the last part of the URL as an "id" of some object to retrieve from GORM or elsewhere. Especially in the case of GORM these are easily guessable as they are typically sequential integers.
Therefore you must assert that the requesting user is allowed to view the object with the requested id before returning the response to the user.
Not doing this is "security through obscurity" which is inevitably breached, just like having a default password of "letmein" and so on.
You must assume that every unprotected URL is publicly accessible one way or another.
Grails supports the concept of dynamic encode/decode methods. A set of standard codecs are bundled with Grails. Grails also supports a simple mechanism for developers to contribute their own codecs that will be recognized at runtime.
Codec Classes
A Grails codec class is a class that may contain an encode closure, a decode closure or both. When a Grails application starts up the Grails framework will dynamically load codecs from the
grails-app/utils/ directory.
The framework will look under
grails-app/utils/ for class names that end with the convention
Codec. For example one of the standard codecs that ship with Grails is
HTMLCodec.
If a codec contains an
encode property assigned a block of code Grails will create a dynamic
encode method and add that method to the Object class with a name representing the codec that defined the encode closure. For example, the
HTMLCodec class defines an
encode block so Grails will attach that closure to the
Object class with the name
encodeAsHTML.
The
HTMLCodec and
URLCodec classes also define a
decode block so Grails will attach those with the names
decodeHTML and
decodeURL. Dynamic codec methods may be invoked from anywhere in a Grails application. For example, consider a case where a report contains a property called 'description' and that description may contain special characters that need to be escaped to be presented in an HTML document. One way to deal with that in a GSP is to encode the description property using the dynamic encode method as shown below:
${report.description.encodeAsHTML()}Decoding is performed using
value.decodeHTML() syntax.
Standard Codecs
HTMLCodecThis codec perfoms HTML escaping and unescaping, so that values you provide can be rendered safely in an HTML page without creating any HTML tags or damaging the page layout. For example, given a value "Don't you know that 2 > 1?" you wouldn't be able to show this safely within an HTML page because the > will look like it closes a tag, which is especially bad if you render this data within an attribute, such as the value attribute of an input field.
Example of usage:
<input name="comment.message" value="${comment.message.encodeAsHTML()}"/>
Note that the HTML encoding does not re-encode apostrophe/single quote so you must use double quotes on attribute values to avoid text with apostrophes messing up your page.
URLCodecURL encoding is required when creating URLs in links or form actions, or any time data may be used to create a URL. It prevents illegal characters getting into the URL to change its meaning, for example a "Apple & Blackberry" is not going to work well as a parameter in a GET request as the ampersand will break the parsing of parameters.
Example of usage:
<a href="/mycontroller/find?searchKey=${lastSearch.encodeAsURL()}">Repeat last search</a>Performs Base64 encode/decode functions. Example of usage:
Your registration code is: ${user.registrationCode.encodeAsBase64()}Will escape Strings so they can be used as valid JavaSctipt strings. Example of usage:
Element.update('${elementId}', '${render(template: "/common/message").encodeAsJavaScript()}')Will encode byte arrays or lists of integers to lowercase hexadecimal strings, and can decode hexadecimal strings into byte arrays. Example of usage:
Selected colour: #${[255,127,255].encodeAsHex()}Will use the MD5 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a lowercase hexadecimal string. Example of usage:
Your API Key: ${user.uniqueID.encodeAsMD5()}Will use the MD5 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a byte array. Example of usage:
byte[] passwordHash = params.password.encodeAsMD5Bytes()
Will use the SHA1 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a lowercase hexadecimal string. Example of usage:
Your API Key: ${user.uniqueID.encodeAsSHA1()}Will use the SHA1 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a byte array. Example of usage:
byte[] passwordHash = params.password.encodeAsSHA1Bytes()
Will use the SHA256 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a lowercase hexadecimal string. Example of usage:
Your API Key: ${user.uniqueID.encodeAsSHA256()}Will use the SHA256 algorithm to digest byte arrays or lists of integers, or the bytes of a string (in default system encoding), as a byte array. Example of usage:
byte[] passwordHash = params.password.encodeAsSHA256Bytes()
Custom Codecs
Applications may define their own codecs and Grails will load them along with the standard codecs. A custom codec class must be defined in the
grails-app/utils/ directory and the class name must end with
Codec. The codec may contain a
static encode block, a
static decode block or both. The block should expect a single argument which will be the object that the dynamic method was invoked on. For Example:
class PigLatinCodec {
static encode = { str ->
// convert the string to piglatin and return the result
}
}
With the above codec in place an application could do something like this:
${lastName.encodeAsPigLatin()}Although there is no current default mechanism for authentication as it is possible to implement authentication in literally thousands of different ways. It is however, trivial to implement a simple authentication mechanism using either
interceptors or
filters.
Filters allow you to apply authentication across all controllers or across a URI space. For example you can create a new set of filters in a class called
grails-app/conf/SecurityFilters.groovy:
class SecurityFilters {
def filters = {
loginCheck(controller:'*', action:'*') {
before = {
if(!session.user && actionName != "login") {
redirect(controller:"user",action:"login")
return false
}
} }
}
}Here the
loginCheck filter will intercept execution
before an action executed and if their is no user in the session and the action being executed is not the
login action then redirect to the
login action.
The
login action itself is trivial too:
def login = {
if(request.get) render(view:"login")
else {
def u = User.findByLogin(params.login)
if(u) {
if(u.password == params.password) {
session.user = u
redirect(action:"home")
}
else {
render(view:"login", model:[message:"Password incorrect"])
}
}
else {
render(view:"login", model:[message:"User not found"])
}
}
}If you need more advanced functionality beyond simple authentication such as authorization, roles etc. then you may want to consider using one of the available security plug-ins.
The Acegi Plug-in is built on the
Spring Acegi project which provides a flexible, extensible framework for building all sorts of authentication and authorization schemes.
The Acegi plug-in requires you to specify a mapping between URIs and roles and provides a default domain model to model people, authorities and request maps. See the
documentation on the wiki for more information.
JSecurity is another Java POJO oriented security framework that again provides a default domain model that models realms, users, roles and permissions. With JSecurity you have to extends a controller base called called
JsecAuthBase in each controller you want secured and then provide an
accessControl block to setup the roles. An example below:
class ExampleController extends JsecAuthBase {
static accessControl = {
// All actions require the 'Observer' role.
role(name: 'Observer') // The 'edit' action requires the 'Administrator' role.
role(name: 'Administrator', action: 'edit') // Alternatively, several actions can be specified.
role(name: 'Administrator', only: [ 'create', 'edit', 'save', 'update' ])
} …
}For more information on the JSecurity plug-in refer to the
JSecurity Quick Start.
Grails provides a number of extension points that allow you to extend anything from the command line interface to the runtime configuration engine. The following sections detail how to go about it.
Creating Plugins
Creating a Grails plugin is a simple matter of running the command:
grails create-plugin [PLUGIN NAME]
This will create a plugin project for the name you specify. Say for example you run
grails create-plugin example. This would create a new plugin project called
example.
The structure of a Grails plugin is exactly the same as a regular Grails project's directory structure, except that in the root of the plugin directory you will find a plugin Groovy file called the "plugin descriptor".
Being a regular Grails project has a number of benefits in that you can immediately get going testing your plugin by running:
The plugin descriptor itself ends with the convention
GrailsPlugin and is found in the root of the plugin project. For example:
class ExampleGrailsPlugin {
def version = 0.1 …
}All plugins must have this class in the root of their directory structure to be valid. The plugin class defines the version of the plugin and optionally various hooks into plugin extension points (covered shortly).
You can also provide additional information about your plugin using several special properties:
title - short one sentence description of your pluginversion - The version of your problem. Valid versions are for example "0.1", "0.2-SNAPSHOT", "0.1.4" etc.grailsVersion - The version of version range of Grails that the plugin supports. eg. "1.1 > *"author - plug-in author's nameauthorEmail - plug-in author's contact e-maildescription - full multi-line description of plug-in's featuresdocumentation - URL where plug-in's documentation can be found
Here is an example from
Quartz Grails pluginclass QuartzGrailsPlugin {
def version = "0.1"
def grailsVersion = "1.1 > *"
def author = "Sergey Nebolsin"
def authorEmail = "nebolsin@gmail.com"
def title = "This plugin adds Quartz job scheduling features to Grails application."
def description = '''
Quartz plugin allows your Grails application to schedule jobs to be
executed using a specified interval or cron expression. The underlying
system uses the Quartz Enterprise Job Scheduler configured via Spring,
but is made simpler by the coding by convention paradigm.
'''
def documentation = "http://grails.org/Quartz+plugin" …
}Installing & Distributing Plugins
To distribute a plugin you need to navigate to its root directory in a terminal window and then type:
This will create a zip file of the plugin starting with
grails- then the plugin name and version. For example with the example plug-in created earlier this would be
grails-example-0.1.zip. The
package-plugin command will also generate
plugin.xml file which contains machine-readable information about plugin's name, version, author, and so on.
Once you have a plugin distribution file you can navigate to a Grails project and type:
grails install-plugin /path/to/plugin/grails-example-0.1.zip
If the plugin is hosted on a remote HTTP server you can also do:
grails install-plugin http://myserver.com/plugins/grails-example-0.1.zip
Notes on excluded Artefacts
Although the
create-plugin command creates certain files for you so that the plug-in can be run as a Grails application, not all of these files are included when packaging a plug-in. The following is a list of artefacts created, but not included by
package-plugin:
grails-app/conf/DataSource.groovygrails-app/conf/UrlMappings.groovybuild.xml- Everything within
/web-app/WEB-INF
If you need artefacts within
WEB-INF it is recommended you use the
_Install.groovy script (covered later), which is executed when a plug-in is installed, to provide such artefacts. In addition, although
UrlMappings.groovy is excluded you are allowed to include a
UrlMappings definition with a different name, such as
FooUrlMappings.groovy.
Distributing Plugins in Grails Plugins Repository
The preferred way of plugin distributing is to publish it under Grails Plugins Repository. This will make your plugin visible to the
list-plugins command:
Which lists all plugins in the Grails Plugin repository and also the
plugin-info command:
grails plugin-info [plugin-name]
Which outputs more information based on the meta info entered into the plug-in descriptor.
If you have created a Grails plug-in and want it to be hosted in the central repository take a look at the wiki page , which details how to go about releasing your plugin in the repository.
When you have access to the Grails Plug-in repository to release your plugin you simply have to execute the
release-plugin command:
This will automatically commit changes to SVN, do some tagging and make your changes available via the
list-plugins command.
Configuring Additional Repositories
By default when you use the
list-plugins,
install-plugin and
release-plugin command they work against the central repository hosted at http://plugins.grails.org.
However, Grails supports the notion of multiple plugin repositories. To configure multiple repositories you can using the
grails-app/conf/BuildConfig.groovy file:
grails.plugin.repos.discovery.myRepository="http://svn.codehaus.org/grails/trunk/grails-test-plugin-repo"
grails.plugin.repos.distribution.myRepository="https://svn.codehaus.org/grails/trunk/grails-test-plugin-repo"
Repositories are split into those used for discovery over HTTP and those used for distribution, typically over HTTPS. You can also provide these settings in the
USER_HOME/.grails/settings.groovy file if you prefer to share the same settings across multiple projects.
Once this is done the
list-plugins,
install-plugin and
plugin-info commands will automatically resolve against the newly configured repository. If you want to list only the plugins from the repository you can use its alias to do so:
grails list-plugins -repository=myRepository
Additionally, if you want to distribute a plugin within the configured repository you can do so with the
release-plugin command:
grails release-plugin -repository=myRepository
Secured Plugin Repositories
By default when using a repository URL starting with the
https:// protocol, Grails will prompt you for a username and password. If you prefer
not to get these prompts then you can specify the username and password to use in your
~/.grails/settings.groovy file as follows:
grails.plugin.repos.discovery.myRepo="https://user01:password01@myserver.com"
The format is:
PROTOCOL://USERNAME:PASSWORD@SERVER
With this set Grails will use the specified username and password rather than prompting you for one.
Configuring Repository Search Order
A common use case for having your own plugin repository is when you want to override or provide a modified version of an existing plugin within the central repository.
However, by default Grails will search repository in a preset order. The repositories it will search are as follows:
default - The default repository found at http://plugins.grails.orgcore - The repository for plugins provides by the framework (such as the hibernate plugin)
If you add an additional repository then Grails will search the repository you have defined last, meaning it is not possible to override a plugin in the central repository unless you change the search order. To change the repository search order you can do the following:
grails.plugin.repos.resolveOrder=['myRepository','default','core']
In the above case the repository called
myRepository will be searched before the default one. In addition, if you remove the built in repositories from the list you can prevent Grails from searching these repositories at all:
grails.plugin.repos.resolveOrder=['myRepository']
This is useful in a circumstance where you don't want Grails to perform any internet lookups when searching for plugins.
As as mentioned previously, a plugin is merely a regular Grails application with a contained plug-in descriptors. However when installed, the structure of a plugin differs slightly. For example, take a look at this plugin directory structure:
+ grails-app
+ controllers
+ domain
+ taglib
etc.
+ lib
+ src
+ java
+ groovy
+ web-app
+ js
+ cssEssentially when a plugin is installed into a project, the contents of the
grails-app directory will go into a directory such as
plugins/example-1.0/grails-app. They
will not be copied into the main source tree. A plugin never interferes with a project's primary source tree.
Dealing with static resources is slightly different. When developing a plugin, just like an application, all static resources can go in the
web-app directory. You can then link to static resources just like in an application (example below links to a javascript source):
<g:resource dir="js" file="mycode.js" />
When you run the plugin in development mode the link to the resource will resolve to something like
/js/mycode.js. However, when the plugin is installed into an application the path will automatically change to something like
/plugin/example-0.1/js/mycode.js and Grails will deal with making sure the resources are in the right place.
There is a special
pluginContextPath variable that can be used whilst both developing the plugin and when in the plugin is installed into the application to find out what the correct path to the plugin is.
At runtime the
pluginContextPath variable will either evaluate to an empty string or
/plugins/example depending on whether the plugin is running standalone or has been installed in an application
Java & Groovy code that the plugin provides within the lib and
src/java and
src/groovy directories will be compiled into the main project's
web-app/WEB-INF/classes directory so that they are made available at runtime.
Adding a new Script
A plugin can add a new script simply by providing the relevant Gant script within the scripts directory of the plugin:
+ MyPlugin.groovy
+ scripts <-- additional scripts here
+ grails-app
+ controllers
+ services
+ etc.
+ libAdding a new Controller, Tag Library or Service
A plugin can add a new controller, tag libraries, service or whatever by simply creating the relevant file within the
grails-app tree. Note that when the plugin is installed it will be loaded from where it is installed and not copied into the main application tree.
+ ExamplePlugin.groovy
+ scripts
+ grails-app
+ controllers <-- additional controllers here
+ services <-- additional services here
+ etc. <-- additional XXX here
+ libProviding Views, Templates and View resolution
When a plug-in provides a controller it may also provide default views to be rendered. This is an excellent way to modularize your application through plugins. The way it works is that Grails' view resolution mechanism will first look the view in the application it is installed into and if that fails will attempt to look for the view within the plug-in.
For example given a
AmazonGrailsPlugin plug-n provided controller called
BookController if the action being executed is
list, Grails will first look for a view called
grails-app/views/book/list.gsp then if that fails will look for the same view relative to the plug-in.
Note however that if the view uses templates that are also provided by the plugin then the following syntax may be necessary:
<g:render template="fooTemplate" plugin="amazon"/>
Note the usage of the
plugin attribute, which contains the name of the plugin where the template resides. If this is not specified then Grails will look for the template relative to the application.
Excluded Artefacts
Note that by default, when packaging a plug-in, Grails will excludes the following files from the packaged plug-in:
- grails-app/conf/DataSource.groovy
- grails-app/conf/UrlMappings.groovy
- Everything under web-app/WEB-INF
If your plug-in does require files under the
web-app/WEB-INF directory it is recommended that you modify the plug-in's
scripts/_Install.groovy Gant script to install these artefacts into the target project's directory tree.
In addition, the default
UrlMappings.groovy file is excluded to avoid naming conflicts, however you are free to add a UrlMappings definition under a different name which
will be included. For example a file called
grails-app/conf/BlogUrlMappings.groovy is fine.
Additionally the list of includes is extensible via the
pluginExcludes property:
// resources that are excluded from plugin packaging
def pluginExcludes = [
"grails-app/views/error.gsp"
]This is useful, for example, if you want to include demo or test resources in the plugin repository, but not include them in the final distribution.
Before moving onto looking at providing runtime configuration based on conventions you first need to understand how to evaluated those conventions from a plug-in. Essentially every plugin has an implicit
application variable which is an instance of the
GrailsApplication interface.
The
GrailsApplication interface provides methods to evaluate the conventions within the project and internally stores references to all classes within a GrailsApplication using the
GrailsClass interface.
A
GrailsClass represents a physical Grails resources such as a controller or a tag library. For example to get all
GrailsClass instances you can do:
application.allClasses.each { println it.name }There are a few "magic" properties that the
GrailsApplication instance possesses that allow you to narrow the type of artefact you are interested in. For example if you only want to controllers you can do:
application.controllerClasses.each { println it.name }The dynamic method conventions are as follows:
*Classes - Retrieves all the classes for a particular artefact name. Example application.controllerClasses.get*Class - Retrieves a named class for a particular artefact. Example application.getControllerClass("ExampleController")is*Class - Returns true if the given class is of the given artefact type. Example application.isControllerClass(ExampleController.class)
The
GrailsClass interface itself provides a number of useful methods that allow you to further evaluate and work with the conventions. These include:
getPropertyValue - Gets the initial value of the given property on the classhasProperty - Returns true if the class has the specified propertynewInstance - Creates a new instance of this class.getName - Returns the logical name of the class in the application without the trailing convention part if applicablegetShortName - Returns the short name of the class without package prefixgetFullName - Returns the full name of the class in the application with the trailing convention part and with the package namegetPropertyName - Returns the name of the class as a property namegetLogicalPropertyName - Returns the logical property name of the class in the application without the trailing convention part if applicablegetNaturalName - Returns the name of the property in natural terms (eg. 'lastName' becomes 'Last Name')getPackageName - Returns the package name
For a full reference refer to the
javadoc API.
Post-Install Configuration and Participating in Upgrades
Grails plug-ins can do post-install configuration and participate in application upgrade process (the
upgrade command). This is achieved via two specially named scripts under
scripts directory of the plugin -
_Install.groovy and
_Upgrade.groovy.
_Install.groovy is executed after the plugin has been installed and
_Upgrade.groovy is executed each time the user upgrades his application with
upgrade command.
These scripts are normal
Gant scripts so you can use the full power of Gant. An addition to the standard Gant variables is the
pluginBasedir variable which points at the plugin installation basedir.
As an example the below
_Install.groovy script will create a new directory type under the
grails-app directory and install a configuration template:
Ant.mkdir(dir:"${basedir}/grails-app/jobs")
Ant.copy(file:"${pluginBasedir}/src/samples/SamplePluginConfiguration.groovy",
todir:"${basedir}/grails-app/conf")// To access Grails home you can use following code:
// Ant.property(environment:"env")
// grailsHome = Ant.antProject.properties."env.GRAILS_HOME"Scripting events
It is also possible to hook into command line scripting events through plug-ins. These are events triggered during execution of Grails target and plugin scripts.
For example, you can hook into status update output (i.e. "Tests passed", "Server running") and the creation of files or artefacts.
A plug-in merely has to provide an
_Events.groovy script to listen to the required events. Refer the documentation on
Hooking into Events for further information.
Grails provides a number of hooks to leverage the different parts of the system and perform runtime configuration by convention.
Hooking into the Grails Spring configuration
First, you can hook in Grails runtime configuration by providing a property called
doWithSpring which is assigned a block of code. For example the following snippet is from one of the core Grails plugins that provides
i18n support:
import org.springframework.web.servlet.i18n.CookieLocaleResolver;
import org.springframework.web.servlet.i18n.LocaleChangeInterceptor;
import org.springframework.context.support.ReloadableResourceBundleMessageSource;class I18nGrailsPlugin { def version = 0.1 def doWithSpring = {
messageSource(ReloadableResourceBundleMessageSource) {
basename = "WEB-INF/grails-app/i18n/messages"
}
localeChangeInterceptor(LocaleChangeInterceptor) {
paramName = "lang"
}
localeResolver(CookieLocaleResolver)
}
}This plugin sets up the Grails
messageSource bean and a couple of other beans to manage Locale resolution and switching. It using the
Spring Bean Builder syntax to do so.
Participating in web.xml Generation
Grails generates the
WEB-INF/web.xml file at load time, and although plugins cannot change this file directly, they can participate in the generation of the file. Essentially a plugin can provide a
doWithWebDescriptor property that is assigned a block of code that gets passed the
web.xml as a
XmlSlurper GPathResult.
Consider the below example from the
ControllersPlugin:
def doWithWebDescriptor = { webXml ->
def mappingElement = webXml.'servlet-mapping'
def lastMapping = mappingElement[mappingElement.size()-1]
lastMapping + {
'servlet-mapping' {
'servlet-name'("grails")
'url-pattern'("*.dispatch")
}
}
}Here the plugin goes through gets a reference to the last
<servlet-mapping> element and appends Grails' servlet to the end of it using XmlSlurper's ability to programmatically modify XML using closures and blocks.
Doing Post Initialisation Configuration
Sometimes it is useful to be able do some runtime configuration after the Spring
ApplicationContext has been built. In this case you can define a
doWithApplicationContext closure property.
class SimplePlugin {
def name="simple"
def version = 1.1 def doWithApplicationContext = { appCtx ->
SessionFactory sf = appCtx.getBean("sessionFactory")
// do something here with session factory
}
}The Basics
Grails plugins allow you to register dynamic methods with any Grails managed or other class at runtime. New methods can only be added within a
doWithDynamicMethods closure of a plugin.
For Grails managed classes like controllers, tag libraries and so forth you can add methods, constructors etc. using the
ExpandoMetaClass mechanism by accessing each controller's
MetaClass:
class ExamplePlugin {
def doWithDynamicMethods = { applicationContext ->
application.controllerClasses.each { controllerClass ->
controllerClass.metaClass.myNewMethod = {-> println "hello world" }
}
}
}In this case we use the implicit application object to get a reference to all of the controller classes' MetaClass instances and then add a new method called
myNewMethod to each controller.
Alternatively, if you know before hand the class you wish the add a method to you can simple reference that classes
metaClass property:
class ExamplePlugin { def doWithDynamicMethods = { applicationContext ->
String.metaClass.swapCase = {->
def sb = new StringBuffer()
delegate.each {
sb << (Character.isUpperCase(it as char) ?
Character.toLowerCase(it as char) :
Character.toUpperCase(it as char))
}
sb.toString()
} assert "UpAndDown" == "uPaNDdOWN".swapCase()
}
}In this example we add a new method
swapCase to
java.lang.String directly by accessing its
metaClass.
Interacting with the ApplicationContext
The
doWithDynamicMethods closure gets passed the Spring
ApplicationContext instance. This is useful as it allows you to interact with objects within it. For example if you where implementing a method to interact with Hibernate you could use the
SessionFactory instance in combination with a
HibernateTemplate:
import org.springframework.orm.hibernate3.HibernateTemplateclass ExampleHibernatePlugin { def doWithDynamicMethods = { applicationContext -> application.domainClasses.each { domainClass -> domainClass.metaClass.static.load = { Long id->
def sf = applicationContext.sessionFactory
def template = new HibernateTemplate(sf)
template.load(delegate, id)
}
}
}
}Also because of the autowiring and dependency injection capability of the Spring container you can implement more powerful dynamic constructors that use the application context to wire dependencies into your object at runtime:
class MyConstructorPlugin { def doWithDynamicMethods = { applicationContext ->
application.domainClasses.each { domainClass ->
domainClass.metaClass.constructor = {->
return applicationContext.getBean(domainClass.name)
}
} }
}Here we actually replace the default constructor with one that looks up prototyped Spring beans instead!
Monitoring Resources for Changes
Often it is valuable to monitor resources for changes and then reload those changes when they occur. This is how Grails implements advanced reloading of application state at runtime. For example, consider the below simplified snippet from the
ServicesPlugin that Grails comes with:
class ServicesGrailsPlugin {
…
def watchedResources = "file:./grails-app/services/*Service.groovy" …
def onChange = { event ->
if(event.source) {
def serviceClass = application.addServiceClass(event.source)
def serviceName = "${serviceClass.propertyName}"
def beans = beans {
"$serviceName"(serviceClass.getClazz()) { bean ->
bean.autowire = true
}
}
if(event.ctx) {
event.ctx.registerBeanDefinition(serviceName,
beans.getBeanDefinition(serviceName))
}
}
}
}Firstly it defines a set of
watchedResources as either a String or a List of strings that contain either the references or patterns of the resources to watch. If the watched resources is a Groovy file, when it is changed it will automatically be reloaded and passed into the
onChange closure inside the
event object.
The
event object defines a number of useful properties:
event.source - The source of the event which is either the reloaded class or a Spring Resourceevent.ctx - The Spring ApplicationContext instanceevent.plugin - The plugin object that manages the resource (Usually this)event.application - The GrailsApplication instance
From these objects you can evaluate the conventions and then apply the appropriate changes to the
ApplicationContext and so forth based on the conventions, etc. In the "Services" example above, a new services bean is re-registered with the
ApplicationContext when one of the service classes changes.
Influencing Other Plugins
As well as being able to react to changes that occur when a plugin changes, sometimes one plugin needs to "influence" another plugin.
Take for example the Services & Controllers plugins. When a service is reloaded, unless you reload the controllers too, problems will occur when you try to auto-wire the reloaded service into an older controller Class.
To get round this, you can specify which plugins another plugin "influences". What this means is that when one plugin detects a change, it will reload itself and then reload all influenced plugins. See this snippet from the
ServicesGrailsPlugin:
def influences = ['controllers']
Observing other plugins
If there is a particular plugin that you would like to observe for changes but not necessary watch the resources that it monitors you can use the "observe" property:
def observe = ["controllers"]
In this case when a controller is changed you will also receive the event chained from the controllers plugin. It is also possible for a plugin to observe all loaded plugins by using a wildcard:
The Logging plugin does exactly this so that it can add the
log property back to
any artefact that changes while the application is running.
Controlling Plug-in Dependencies
Plug-ins often depend on the presence of other plugins and can also adapt depending on the presence of others. To cover this, a plugin can define two properties. The first is called
dependsOn. For example, take a look at this snippet from the Grails Hibernate plugin:
class HibernateGrailsPlugin {
def version = 1.0
def dependsOn = [dataSource:1.0,
domainClass:1.0,
i18n:1.0,
core: 1.0]}As the above example demonstrates the Hibernate plugin is dependent on the presence of 4 plugins: The
dataSource plugin, The
domainClass plugin, the
i18n plugin and the
core plugin.
Essentially the dependencies will be loaded first and then the Hibernate plugin. If all dependencies do not load, then the plugin will not load.
The
dependsOn property also supports a mini expression language for specifying version ranges. A few examples of the syntax can be seen below:
def dependsOn = [foo:"* > 1.0"]
def dependsOn = [foo:"1.0 > 1.1"]
def dependsOn = [foo:"1.0 > *"]
When the wildcard * character is used it denotes "any" version. The expression syntax also excludes any suffixes such as -BETA, -ALPHA etc. so for example the expression "1.0 > 1.1" would match any of the following versions:
- 1.1
- 1.0
- 1.0.1
- 1.0.3-SNAPSHOT
- 1.1-BETA2
Controlling Load Order
Using
dependsOn establishes a "hard" dependency in that if the dependency is not resolved, the plugin will give up and won't load. It is possible though to have a "weaker" dependency using the
loadAfter property:
def loadAfter = ['controllers']
Here the plugin will be loaded after the
controllers plugin if it exists, otherwise it will just be loaded. The plugin can then adapt to the presence of the other plugin, for example the Hibernate plugin has this code in the
doWithSpring closure:
if(manager?.hasGrailsPlugin("controllers")) {
openSessionInViewInterceptor(OpenSessionInViewInterceptor) {
flushMode = HibernateAccessor.FLUSH_MANUAL
sessionFactory = sessionFactory
}
grailsUrlHandlerMapping.interceptors << openSessionInViewInterceptor
}Here the Hibernate plugin will only register an
OpenSessionInViewInterceptor if the
controllers plugin has been loaded. The manager variable is an instance of the
GrailsPluginManager interface and it provides methods to interact with other plugins and the
GrailsPluginManager itself from any plugin.
Web services are all about providing a web API onto your web application and are typically implemented in either
SOAP or
REST.
REST is not really a technology in itself, but more an architectural pattern. REST is extremely simple and just involves using plain XML or JSON as a communication medium, combined with URL patterns that are "representational" of the underlying system and HTTP methods such as GET, PUT, POST and DELETE.
Each HTTP method maps to an action. For example GET for retrieving data, PUT for creating data, POST for updating and so on. In this sense REST fits quite well with
CRUD.
URL patterns
The first step to implementing REST with Grails is to provide RESTful
URL mappings:
static mappings = {
"/product/$id?"(resource:"product")
}What this does is map the URI
/product onto a
ProductController. Each HTTP method such as GET, PUT, POST and DELETE map to unique actions within the controller as outlined by the table below:
| Method | Action |
|---|
GET | show |
PUT | update |
POST | save |
DELETE | delete |
You can alter how HTTP methods by using the capability of URL Mappings to
map to HTTP methods:
"/product/$id"(controller:"product"){
action = [GET:"show", PUT:"update", DELETE:"delete", POST:"save"]
}However, unlike the
resource argument used previously, in this case Grails will not provide automatic XML or JSON marshaling for you unless you specify the
parseRequest argument in the URL mapping:
"/product/$id"(controller:"product", parseRequest:true){
action = [GET:"show", PUT:"update", DELETE:"delete", POST:"save"]
}HTTP Methods
In the previous section you saw how you can easily define URL mappings that map specific HTTP methods onto specific controller actions. Writing a REST client that then sends a specific HTTP method is then trivial (example in Groovy's HTTPBuilder module):
import groovyx.net.http.*
import static groovyx.net.http.ContentType.JSONdef http = new HTTPBuilder("http://localhost:8080/amazon") http.request(Method.GET, JSON) {
url.path = '/book/list'
response.success = {resp, json ->
json.books.each { book ->
println book.title
}
}
}However, issuing a request with a method other than
GET or
POST from a regular browser is not possible without some help from Grails. When defining a
form you can specify an alternative method such as
DELETE:
<g:form controller="book" method="DELETE">
..
</g:form>
Grails will send a hidden parameter called
_method, which will be used as the request's HTTP method. Another alternative for changing the method for non-browser clients is to use the
X-HTTP-Method-Override to specify the alternative method name.
XML Marshaling - Reading
The controller implementation itself can use Grails'
XML marshaling support to implement the GET method:
import grails.converters.*
class ProductController {
def show = {
if(params.id && Product.exists(params.id)) {
def p = Product.findByName(params.id)
render p as XML
}
else {
def all = Product.list()
render all as XML
}
}
..
}Here what we do is if there is an
id we search for the
Product by name and return it otherwise we return all Products. This way if we go to
/products we get all products, otherwise if we go to
/product/MacBook we only get a MacBook.
XML Marshalling - Updating
To support updates such as
PUT and
POST you can use the
params object which Grails enhances with the ability to read an incoming XML packet. Given an incoming XML packet of:
<?xml version="1.0" encoding="ISO-8859-1"?>
<product>
<name>MacBook</name>
<vendor id="12">
<name>Apple</name>
</vender>
</product>You can read this XML packet using the same techniques described in the
Data Binding section via the
params object:
def save = {
def p = new Product(params['product']) if(p.save()) {
render p as XML
}
else {
render p.errors
}
}In this example by indexing into the
params object using the key
'product' we can automatically create and bind the XML using the constructor of the
Product class. An interesting aspect of the line:
def p = new Product(params['product'])
Is that it requires no code changes to deal with a form submission that submits form data than it does to deal with an XML request. The exact same technique can be used with a JSON request too.
If you require different responses to different clients (REST, HTML etc.) you can use content negotation
The
Product object is then saved and rendered as XML, otherwise an error message is produced using Grails'
validation capabilities in the form:
<error>
<message>The property 'title' of class 'Person' must be specified</message>
</error>
There are several plugins that add SOAP support to Grails depending on your preferred approach. For Contract First SOAP services there is a
Spring WS plugin, whilst if you want to generate a SOAP API from Grails services there are several plugins that do this including:
Most of the SOAP integrations integrate with Grails
services via the
exposes static property. The below example is taken from the XFire plugin:
class BookService { static expose=['xfire'] Book[] getBooks(){
Book.list() as Book[]
}
}The WSDL can then be accessed at the location:
http://127.0.0.1:8080/your_grails_app/services/book?wsdlFor more information on the XFire plug-in refer
the documentation on the wiki.
No direct support is provided for RSS or Atom within Grails. You could construct RSS or ATOM feeds with the
render method's XML capability. There is however a
Feeds plug-in available for Grails that provides a RSS and Atom builder using the popular
ROME library. An example of its usage can be seen below:
def feed = {
render(feedType:"rss", feedVersion:"2.0") {
title = "My test feed"
link = "http://your.test.server/yourController/feed" Article.list().each() {
entry(it.title) {
link = "http://your.test.server/article/${it.id}"
it.content // return the content
}
}
}
}This section is for advanced users and those who are interested in how Grails integrates with and builds on the
Spring Framework This section is also useful for
plug-in developers considering doing runtime configuration Grails.
Grails is actually a
Spring MVC application in disguise. Spring MVC is the Spring framework's built-in MVC web application framework. Although Spring MVC suffers from the same difficulties as frameworks like Struts in terms of its ease of use, it is superbly designed and architected and was, for Grails, the perfect framework to build another framework on top of.
Grails leverages Spring MVC in the following areas:
- Basic controller logic - Grails subclasses Spring's DispatcherServlet and uses it to delegate onto Grails controllers
- Data Binding and Validation - Grails' validation and data binding capabilities are built on those provided by Spring
- Runtime configuration - Grails' entire runtime convention based system is wired together by a Spring ApplicationContext
- Transactions - Grails uses Spring's transaction management in GORM
In other words Grails has Spring embedded running all the way through it.
The Grails ApplicationContext
Spring developers are often keen to understand how the Grails
ApplicationContext instance is constructed. The basics of it are as follows.
- Grails constructs a parent
ApplicationContext from the web-app/WEB-INF/applicationContext.xml. This ApplicationContext sets up the GrailsApplication instance and the GrailsPluginManager.
- Using this
ApplicationContext as a parent Grails' analyses the conventions with the GrailsApplication instance and constructs a child ApplicationContext that is used as the root ApplicationContext of the web application
Configured Spring Beans
Most of Grails' configuration happens at runtime. Each
plug-in may configure Spring beans that are registered with the
ApplicationContext. For a reference as to which beans are configured refer to the reference guide which describes each of the Grails plug-ins and which beans they configure.
Using XML
Beans can be configured using the
grails-app/conf/spring/resources.xml file of your Grails application. This file is typical Spring XML file and the Spring documentation has an
excellent reference on how to go about configuration Spring beans. As a trivial example you can configure a bean with the following syntax:
<bean id="myBean" class="my.company.MyBeanImpl"></bean>
Once configured the bean, in this case named
myBean, can be auto-wired into most Grails types including controllers, tag libraries, services and so on:
class ExampleController { def myBean
}Referencing Existing Beans
Beans declared in
resources.xml can also reference Grails classes by convention. For example if you need a reference to a service such as
BookService in your bean you use the property name representation of the class name. In the case of
BookService this would be
bookService. For example:
<bean id="myBean" class="my.company.MyBeanImpl">
<property name="bookService" ref="bookService" />
</bean>
The bean itself would of course need a public setter, which in Groovy is defined like this:
package my.company
class MyBeanImpl {
BookService bookService
}or in Java like this:
package my.company;
class MyBeanImpl {
private BookService bookService;
public void setBookService(BookService theBookService) {
this.bookService = theBookService;
}
}Since much of Grails configuration is done at runtime by convention many of the beans are not declared anywhere, but can still be referenced inside your Spring configuration. For example if you need a reference to the Grails
DataSource you could do:
<bean id="myBean" class="my.company.MyBeanImpl">
<property name="bookService" ref="bookService" />
<property name="dataSource" ref="dataSource" />
</bean>
Or if you need the Hibernate
SessionFactory this will work:
<bean id="myBean" class="my.company.MyBeanImpl">
<property name="bookService" ref="bookService" />
<property name="sessionFactory" ref="sessionFactory" />
</bean>
For a full reference of the available beans see the Plug-in reference in the reference guide.
Using the Spring DSL
If you want to use the
Spring DSL that Grails provides then you need to create a
grails-app/conf/spring/resources.groovy file and define a property called
beans that is assigned a block:
beans = {
// beans here
}The same configuration for the XML example could be represented as:
beans = {
myBean(my.company.MyBeanImpl) {
bookService = ref("bookService")
}
}The main advantage of this way is that you can now mix logic in within your bean definitions, for example based on the
environment:
import grails.util.*
beans = {
switch(GrailsUtil.environment) {
case "production":
myBean(my.company.MyBeanImpl) {
bookService = ref("bookService")
} break
case "development":
myBean(my.company.mock.MockImpl) {
bookService = ref("bookService")
}
break
}
}This Bean builder in Grails aims to provide a simplified way of wiring together dependencies that uses Spring at its core.
In addition, Spring's regular way of configuration (via XML) is essentially static and very difficult to modify and configure at runtime other than programmatic XML creation which is both error prone and verbose. Grails'
BeanBuilder changes all that by making it possible to programmatically wire together components at runtime thus allowing you to adapt the logic based on system properties or environment variables.
This enables the code to adapt to its environment and avoids unnecessary duplication of code (having different Spring configs for test, development and production environments)
The BeanBuilder class
Grails provides a
grails.spring.BeanBuilder class that uses dynamic Groovy to construct bean definitions. The basics are as follows:
import org.apache.commons.dbcp.BasicDataSource
import org.codehaus.groovy.grails.orm.hibernate.ConfigurableLocalSessionFactoryBean;
import org.springframework.context.ApplicationContext;def bb = new grails.spring.BeanBuilder()bb.beans {
dataSource(BasicDataSource) {
driverClassName = "org.hsqldb.jdbcDriver"
url = "jdbc:hsqldb:mem:grailsDB"
username = "sa"
password = ""
}
sessionFactory(ConfigurableLocalSessionFactoryBean) {
dataSource = dataSource
hibernateProperties = [ "hibernate.hbm2ddl.auto":"create-drop",
"hibernate.show_sql":true ]
}
}ApplicationContext appContext = bb.createApplicationContext()
Within plug-ins and the grails-app/conf/spring/resources.groovy file you don't need to create a new instance of BeanBuilder. Instead the DSL is implicitly available inside the doWithSpring and beans blocks respectively.
The above example shows how you would configure Hibernate with an appropriate data source with the
BeanBuilder class.
Essentially, each method call (in this case
dataSource and
sessionFactory calls) map to the name of the bean in Spring. The first argument to the method is the bean's class, whilst the last argument is a block. Within the body of the block you can set properties on the bean using standard Groovy syntax
Bean references are resolved automatically be using the name of the bean. This can be seen in the example above with the way the
sessionFactory bean resolves the
dataSource reference.
Certain special properties related to bean management can also be set by the builder, as seen in the following code:
sessionFactory(ConfigurableLocalSessionFactoryBean) { bean ->
bean.autowire = 'byName' // Autowiring behaviour. The other option is 'byType'. [autowire]
bean.initMethod = 'init' // Sets the initialisation method to 'init'. [init-method]
bean.destroyMethod = 'destroy' // Sets the destruction method to 'destroy'. [destroy-method]
bean.scope = 'request' // Sets the scope of the bean. [scope]
dataSource = dataSource
hibernateProperties = [ "hibernate.hbm2ddl.auto":"create-drop",
"hibernate.show_sql":true ]
}The strings in square brackets are the names of the equivalent bean attributes in Spring's XML definition.
Using BeanBuilder with Spring MVC
If you want to take advantage of BeanBuilder in a regular Spring MVC application you need to make sure the
grails-spring-<version>.jar file is in your classpath. Once that is done you can need to set the following
<context-param> values in your
/WEB-INF/web.xml file:
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/applicationContext.groovy</param-value>
</context-param>
<context-param>
<param-name>contextClass</param-name>
<param-value>org.codehaus.groovy.grails.commons.spring.GrailsWebApplicationContext</param-value>
</context-param>With that done you can then create a /WEB-INF/applicationContext.groovy file that does the rest:
beans {
dataSource(org.apache.commons.dbcp.BasicDataSource) {
driverClassName = "org.hsqldb.jdbcDriver"
url = "jdbc:hsqldb:mem:grailsDB"
username = "sa"
password = ""
}
}Loading Bean Definitions from the File System
You can use the
BeanBuilder class to load external Groovy scripts that define beans using the same path matching syntax defined here. Example:
def bb = new BeanBuilder()
bb.loadBeans("classpath:*SpringBeans.groovy")def applicationContext = bb.createApplicationContext()Here the
BeanBuilder will load all Groovy files on the classpath ending with
SpringBeans.groovy and parse them into bean definitions. An example script can be seen below:
beans {
dataSource(BasicDataSource) {
driverClassName = "org.hsqldb.jdbcDriver"
url = "jdbc:hsqldb:mem:grailsDB"
username = "sa"
password = ""
}
sessionFactory(ConfigurableLocalSessionFactoryBean) {
dataSource = dataSource
hibernateProperties = [ "hibernate.hbm2ddl.auto":"create-drop",
"hibernate.show_sql":true ]
}
}Adding Variables to the Binding (Context)
If you're loading beans from a script you can set the binding to use by creating a Groovy Binding object:
def binding = new Binding()
binding.foo = "bar"def bb = new BeanBuilder()
bb.binding = binding
bb.loadBeans("classpath:*SpringBeans.groovy")def ctx = bb.createApplicationContext()Using Constructor Arguments
Constructor arguments can be defined using parameters to each method that reside between the class of the bean and the last closure:
bb.beans {
exampleBean(MyExampleBean, "firstArgument", 2) {
someProperty = [1,2,3]
}
}Configuring the BeanDefinition (Using factory methods)
The first argument to the closure is a reference to the bean configuration instance, which you can use to configure factory methods and invoke any method on the
AbstractBeanDefinition class:
bb.beans {
exampleBean(MyExampleBean) { bean ->
bean.factoryMethod = "getInstance"
bean.singleton = false
someProperty = [1,2,3]
}
}As an alternative you can also use the return value of the bean defining method to configure the bean:
bb.beans {
def example = exampleBean(MyExampleBean) {
someProperty = [1,2,3]
}
example.factoryMethod = "getInstance"
}Using Factory beans
Spring defines the concept of factory beans and often a bean is created not from a class, but from one of these factories. In this case the bean has no class and instead you must pass the name of the factory bean to the bean:
bb.beans {
myFactory(ExampleFactoryBean) {
someProperty = [1,2,3]
}
myBean(myFactory) {
name = "blah"
}
}Note in the example above instead of a class we pass a reference to the
myFactory bean into the bean defining method. Another common task is provide the name of the factory method to call on the factory bean. This can be done using Groovy's named parameter syntax:
bb.beans {
myFactory(ExampleFactoryBean) {
someProperty = [1,2,3]
}
myBean(myFactory:"getInstance") {
name = "blah"
}
}Here the
getInstance method on the
ExampleFactoryBean bean will be called in order to create the
myBean bean.
Creating Bean References at Runtime
Sometimes you don't know the name of the bean to be created until runtime. In this case you can use a string interpolation to invoke a bean defining method dynamically:
def beanName = "example"
bb.beans {
"${beanName}Bean"(MyExampleBean) {
someProperty = [1,2,3]
}
}In this case the
beanName variable defined earlier is used when invoking a bean defining method.
Furthermore, because sometimes bean names are not known until runtime you may need to reference them by name when wiring together other beans. In this case using the
ref method:
def beanName = "example"
bb.beans {
"${beanName}Bean"(MyExampleBean) {
someProperty = [1,2,3]
}
anotherBean(AnotherBean) {
example = ref("${beanName}Bean")
}
}
Here the example property of
AnotherBean is set using a runtime reference to the
exampleBean. The
ref method can also be used to refer to beans from a parent
ApplicationContext that is provided in the constructor of the
BeanBuilder:
ApplicationContext parent = ...//
der bb = new BeanBuilder(parent)
bb.beans {
anotherBean(AnotherBean) {
example = ref("${beanName}Bean", true)
}
}Here the second parameter
true specifies that the reference will look for the bean in the parent context.
Using Anonymous (Inner) Beans
You can use anonymous inner beans by setting a property of the bean to a block that takes an argument that is the bean type:
bb.beans {
marge(Person.class) {
name = "marge"
husband = { Person p ->
name = "homer"
age = 45
props = [overweight:true, height:"1.8m"]
}
children = [bart, lisa]
}
bart(Person) {
name = "Bart"
age = 11
}
lisa(Person) {
name = "Lisa"
age = 9
}
}In the above example we set the
marge bean's husband property to a block that creates an inner bean reference. Alternatively if you have a factory bean you can ommit the type and just use passed bean definition instead to setup the factory:
bb.beans {
personFactory(PersonFactory.class)
marge(Person.class) {
name = "marge"
husband = { bean ->
bean.factoryBean = "personFactory"
bean.factoryMethod = "newInstance"
name = "homer"
age = 45
props = [overweight:true, height:"1.8m"]
}
children = [bart, lisa]
}
}Abstract Beans and Parent Bean Definitions
To create an abstract bean definition define a bean that takes no class:
class HolyGrailQuest {
def start() { println "lets begin" }
}
class KnightOfTheRoundTable {
String name
String leader
KnightOfTheRoundTable(String n) {
this.name = n
}
HolyGrailQuest quest def embarkOnQuest() {
quest.start()
}
}def bb = new grails.spring.BeanBuilder()
bb.beans {
abstractBean {
leader = "Lancelot"
}
…
}Here we define an abstract bean that sets that has a
leader property with the value of
"Lancelot". Now to use the abstract bean set it as the parent of the child bean:
bb.beans {
…
quest(HolyGrailQuest)
knights(KnightOfTheRoundTable, "Camelot") { bean ->
bean.parent = abstractBean
quest = quest
}
}
When using a parent bean you must set the parent property of the bean before setting any other properties on the bean!
If you want an abstract bean that has a class you can do it this way:
def bb = new grails.spring.BeanBuilder()
bb.beans {
abstractBean(KnightOfTheRoundTable) { bean ->
bean.'abstract' = true
leader = "Lancelot"
}
quest(HolyGrailQuest)
knights("Camelot") { bean ->
bean.parent = abstractBean
quest = quest
}
}In the above example we create an abstract bean of type
KnightOfTheRoundTable and use the bean argument to set it to abstract. Later we define a knights bean that has no class, but inherits the class from the parent bean.
Using Spring Namespaces
Since Spring 2.0, users of Spring have been granted easier access to key features via XML namespaces. With BeanBuilder you can use any Spring namespace by first declaring it:
xmlns context:"http://www.springframework.org/schema/context"
And then invoking a method that matches the names of the Spring namespace tag and its associated attributes:
context.'component-scan'( 'base-package' :"my.company.domain" )
You can do some useful things with Spring namespaces, such as looking up a JNDI resource:
xmlns jee:"http://www.springframework.org/schema/jee"jee.'jndi-lookup'(id:"dataSource", 'jndi-name':"java:comp/env/myDataSource")
The example above will create a Spring bean with the identifier of
dataSource by performing a JNDI lookup on the given JNDI name. With Spring namespaces you also get full access to all of the powerful AOP support in Spring from BeanBuilder. For example given the following two classes:
class Person {
int age;
String name; void birthday() {
++age;
}
}
class BirthdayCardSender {
List peopleSentCards = []
public void onBirthday(Person person) {
peopleSentCards << person
}
}You can define an AOP aspect that uses a pointcut to detect whenever the
birthday() method is called:
xmlns aop:"http://www.springframework.org/schema/aop"
fred(Person) {
name = "Fred"
age = 45
}birthdayCardSenderAspect(BirthdayCardSender)aop {
config("proxy-target-class":true) {
aspect( id:"sendBirthdayCard",ref:"birthdayCardSenderAspect" ) {
after method:"onBirthday", pointcut: "execution(void ..Person.birthday()) and this(person)"
}
}
}Grails supports the notion of property placeholder configuration through an extended version of Spring's
PropertyPlaceholderConfigurer, which is typically useful when used in combination with
externalized configuration.
Settings defined in either
ConfigSlurper scripts of Java properties files can be used as placeholder values for Spring configuration in
grails-app/conf/spring/resources.xml. For example given the following entries in
grails-app/conf/Config.groovy (or an externalized config):
database.driver="com.mysql.jdbc.Driver"
database.dbname="mysql:mydb"
You can then specify placeholders in
resources.xml as follows using the familiar ${..} syntax:
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName"><value>${database.driver}</value></property>
<property name="url"><value>jdbc:${database.dbname}</value></property>
</bean>Grails supports setting of bean properties via
configuration. This is often useful when used in combination with
externalized configuration.
Essentially you define a
beans block with the names of beans and their values:
beans {
bookService {
webServiceURL = "http://www.amazon.com"
}
}The general format is:
[bean name].[property name] = [value]
The same configuration in a Java properties file would be:
beans.bookService.webServiceURL=http://www.amazon.com
If
GORM (Grails Object Relational Mapping) is not flexible enough for your liking you can alternatively map your domain classes using Hibernate, either via XML mapping files or JPA annotations. You will be able to map Grails domain classes onto a wider range of legacy systems and be more flexible in the creation of your database schema. Best of all, you will still be able to call all of the dynamic persistent and query methods provided by GORM!
Mapping your domain classes via XML is pretty straightforward. Simply create a
hibernate.cfg.xml file in your project's
grails-app/conf/hibernate directory that contains the following:
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE hibernate-configuration PUBLIC
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<mapping resource="org.example.Book.hbm.xml"/>
…
</session-factory>
</hibernate-configuration>The individual mapping files, like 'org.example.Book.hbm.xml' in the above example, also go into the
grails-app/conf/hibernate directory. To find out how to map domain classes via XML, check out the
Hibernate manual.
If the default location of the
hibernate.cfg.xml file doesn't suit you, you can change it by specifying an alternative location in
grails-app/conf/DataSource.groovy:
hibernate {
config.location = "file:/path/to/my/hibernate.cfg.xml"
}or even a list of locations:
hibernate {
config.location = ["file:/path/to/one/hibernate.cfg.xml","file:/path/to/two/hibernate.cfg.xml"]
}Grails also allows you to write your domain model in Java or re-use an existing one that already has Hibernate mapping files. Simply place the mapping files into
grails-app/conf/hibernate and either put the Java files in
src/java or (if the domain model is stored in a JAR) the packaged classes into the project's
lib directory. You still need the
hibernate.cfg.xml though!
To map a domain class via annotations, create a new class in
src/java and use the annotations defined as part of the EJB 3.0 spec (for more info on this see the
Hibernate Annotations Docs):
package com.books;
@Entity
public class Book {
private Long id;
private String title;
private String description;
private Date date; @Id
@GeneratedValue
public Long getId() {
return id;
} public void setId(Long id) {
this.id = id;
} public String getTitle() {
return title;
} public void setTitle(String title) {
this.title = title;
} public String getDescription() {
return description;
} public void setDescription(String description) {
this.description = description;
}
}Once that is done you need to register the class with the Hibernate
sessionFactory by adding relevant entries to the
grails-app/conf/hibernate/hibernate.cfg.xml file as follows:
<!DOCTYPE hibernate-configuration SYSTEM
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
<session-factory>
<mapping package="com.books" />
<mapping class="com.books.Book" />
</session-factory>
</hibernate-configuration>
See the previous section for more information on the
hibernate.cfg.xml file.
When Grails loads it will register the necessary dynamic methods with the class. To see what else you can do with a Hibernate domain class see the section on
Scaffolding.
Even if you use a Java domain model, you can still take advantage of GORM validation. Grails allows you to define constraints through a separate script that you place in the
src/java directory. The script should be in a directory that matches the package of the corresponding domain class and its name should have a
Constraints suffix. For example, if you had a domain class
org.example.Book, then you would create the script
src/java/org/example/BookConstraints.groovy.
The contents of the script should contain a standard GORM constraints block like so:
constraints = {
title(blank: false)
author(blank: false)
}
Once the script is in place, you'll be able to validate instances of your domain class!
Grails committer, Jason Rudolph, took the time to write many useful articles about using Grails with custom Hibernate mappings including:
Scaffolding allows you to auto-generate a whole application for a given domain class including:
- The necessary views
- Controller actions for create/read/update/delete (CRUD) operations
Enabling Scaffolding
The simplest way to get started with scaffolding is to enable scaffolding via the
scaffold property. For the
Book domain class, you need to set the
scaffold property on a controller to true:
class BookController {
def scaffold = true
}The above works because the
BookController follows the same naming convention as the
Book domain class, if we wanted to scaffold a specific domain class you can reference the class directly in the scaffold property:
With that done if you run this grails application the necessary actions and views will be auto-generated at runtime. The following actions are dynamically implemented by default by the runtime scaffolding mechanism:
- list
- show
- edit
- delete
- create
- save
- update
As well as this a CRUD interface will be generated. To access the interface in the above example simply go to
http://localhost:8080/app/bookIf you prefer to keep your domain model in Java and
mapped with Hibernate you can still use scaffolding, simply import the necessary class and set the scaffold property to it.
Dynamic Scaffolding
Note that when using the scaffold property Grails does not use code templates, or code generation to achieve this so you can add your own actions to the scaffolded controller that interact with the scaffolded actions. For example, in the below example,
changeAuthor redirects to the
show action which doesn't actually exist physically:
class BookController {
def scaffold = Book def changeAuthor = {
def b = Book.get( params["id"] )
b.author = Author.get( params["author.id"] )
b.save() // redirect to a scaffolded action
redirect(action:show)
}
}You can also override the scaffolded actions with your own actions if necessary:
class BookController {
def scaffold = Book // overrides scaffolded action to return both authors and books
def list = {
[ "books" : Book.list(), "authors": Author.list() ]
}
}All of this is what is known as "dynamic scaffolding" where the CRUD interface is generated dynamically at runtime. Grails also supports "static" scaffolding which will be discussed in the following sections.
Customizing the Generated Views
The views that Grails generates have some form of intelligence in that they adapt to the
Validation constraints. For example you can change the order that fields appear in the views simply by re-ordering the constraints in the builder:
def constraints = {
title()
releaseDate()
}You can also get the generator to generate lists instead of text inputs if you use the
inList constraint:
def constraints = {
title()
category(inList:["Fiction", "Non-fiction", "Biography"])
releaseDate()
}Or if you use the
range constraint on a number:
def constraints = {
age(range:18..65)
}Restricting the size via a constraint also effects how many characters can be entered in the generated view:
def constraints = {
name(size:0..30)
}Generating Controllers & Views
The above scaffolding features are useful but in real world situations its likely that you will want to customize the logic and views. Grails allows you to generate a controller and the views used to create the above interface via the command line. To generate a controller type:
grails generate-controller Book
Or to generate the views type:
grails generate-views Book
Or to generate everything type:
If you have a domain class in a package or are generating from a
Hibernate mapped class remember to include the fully qualified package name:
grails generate-all com.bookstore.Book
Customizing the Scaffolding templates
The templates used by Grails to generate the controller and views can be customized by installing the templates with the
install-templates command.
Grails applications can be deployed in a number of ways, each of which has its pros and cons.
"grails run-app"
You should be very familiar with this approach by now, since it is the most common method of running an application during the development phase. An embedded Tomcat server is launched that loads the web application from the development sources, thus allowing it to pick up an changes to application files.
This approach is not recommended at all for production deployment because the performance is poor. Checking for and loading changes places a sizable overhead on the server. Having said that,
grails prod run-app removes the per-request overhead and allows you to fine tune how frequently the regular check takes place.
Setting the system property "disable.auto.recompile" to
true disables this regular check completely, while the property "recompile.frequency" controls the frequency. This latter property should be set to the number of seconds you want between each check. The default is currently 3.
"grails run-war"
This is very similar to the previous option, but Tomcat runs against the packaged WAR file rather than the development sources. Hot-reloading is disabled, so you get good performance without the hassle of having to deploy the WAR file elsewhere.
WAR file
When it comes down to it, current java infrastructures almost mandate that web applications are deployed as WAR files, so this is by far the most common approach to Grails application deployment in production. Creating a WAR file is as simple as executing the
war command:
There are also many ways in which you can customise the WAR file that is created. For example, you can specify a path (either absolute or relative) to the command that instructs it where to place the file and what name to give it:
grails war /opt/java/tomcat-5.5.24/foobar.war
Alternatively, you can add a line to
grails-app/conf/BuildConfig.groovy that changes the default location and filename:
grails.war.destFile = "foobar-prod.war"
Of course, any command line argument that you provide overrides this setting.
It is also possible to control what libraries are included in the WAR file, in case you need to avoid conflicts with libraries in a shared folder for example. The default behavior is to include in the WAR file all libraries required by Grails, plus any libraries contained in plugin "lib" directories, plus any libraries contained in the application's "lib" directory. As an alternative to the default behavior you can explicitly specify the complete list of libraries to include in the WAR file by setting the properties
grails.war.dependencies and
grails.war.java5.dependencies in Config.groovy to either lists of Ant include patterns or closures containing AntBuilder syntax. Closures are invoked from within an Ant "copy" step, so only elements like "fileset" can be included, whereas each item in a pattern list is included. Any closure or pattern assigned to the latter property will be included in addition to
grails.war.dependencies only if you are running JDK 1.5 or above.
Be careful with these properties: if any of the libraries Grails depends on are missing, the application will almost certainly fail. Here is an example that includes a small subset of the standard Grails dependencies:
def deps = [
"hibernate3.jar",
"groovy-all-*.jar",
"standard-${servletVersion}.jar",
"jstl-${servletVersion}.jar",
"oscache-*.jar",
"commons-logging-*.jar",
"sitemesh-*.jar",
"spring-*.jar",
"log4j-*.jar",
"ognl-*.jar",
"commons-*.jar",
"xstream-1.2.1.jar",
"xpp3_min-1.1.3.4.O.jar" ]grails.war.dependencies = {
fileset(dir: "libs") {
deps.each { pattern ->
include(name: pattern)
}
}
}This example only exists to demonstrate the syntax for the properties. If you attempt to use it as is in your own application, the application will probably not work. You can find a list of dependencies required by Grails in the "dependencies.txt" file that resides in the root directory of the unpacked distribution. You can also find a list of the default dependencies included in WAR generation in the "War.groovy" script - see the "DEFAULT_DEPS" and "DEFAULT_J5_DEPS" variables.
The remaining two configuration options available to you are
grails.war.copyToWebApp and
grails.war.resources. The first of these allows you to customise what files are included in the WAR file from the "web-app" directory. The second allows you to do any extra processing you want before the WAR file is finally created.
// This closure is passed the command line arguments used to start the
// war process.
grails.war.copyToWebApp = { args ->
fileset(dir:"web-app") {
include(name: "js/**")
include(name: "css/**")
include(name: "WEB-INF/**")
}
}// This closure is passed the location of the staging directory that
// is zipped up to make the WAR file, and the command line arguments.
// Here we override the standard web.xml with our own.
grails.war.resources = { stagingDir, args ->
copy(file: "grails-app/conf/custom-web.xml", tofile: "${stagingDir}/WEB-INF/web.xml")
}Application servers
Ideally you should be able to simply drop a WAR file created by Grails into any application server and it should work straight away. However, things are rarely ever this simple. The
Grails website contains an up-to-date list of application servers that Grails has been tested with, along with any additional steps required to get a Grails WAR file working.
