You will need to upgrade your Grails version defined in gradle.properties.

Grails 3 app’s gradle.properties

Grails 4 app’s gradle.properties

If you were using GORM, you will need to update the version defined in gradle.properties.

Grails 3 app’s gradle.properties

Grails 4 app’s gradle.properties

Grails 4.0 is built on Spring 5 and Spring Boot 2.1. See the migration guide and release notes if you are using Spring specific features.

Grails 4.x supports a minimum version of Hibernate 5.4 and GORM 7.x. Several changes have been made to GORM to support the newer version of Hibernate and simplify GORM itself.

The details of these changes are covered in the GORM upgrade documentation.

Please check the Spring Boot Actuator documentation since it has changed substantially from Spring Boot 1.5 the version Grails 3.x used.

If you had configuration such as:

replace it with:

Grails 4 applications include Spring Boot Developer Tools dependencies in the build.gradle build script. If you are migrating a Grails 3.x app, please include the next set of dependencies:

You can use Spring Developer Tools in combination with a browser extension such as the Chrome LiveReload extension to get automatic browser refresh when you change anything in your Grails application.

Grails 4 is built on top of Spring Boot 2.1. Grails 3 apps were built on top of Spring Boot 1.x.

Your Grails 3 app’s build.gradle may have such configuration:

Grails 4 apps are built on top of Spring Boot 2.1. Starting from Spring Boot 2.0, the addResources property no longer exists. Instead, you need to set the sourceResources property to the source set that you want to use. Typically that’s sourceSets.main. This is described in the Spring Boot Gradle plugin’s documentation.

Your Grails 4 app’s build.gradle can be configured:

Spring Boot’s new Gradle Plugin:

If you had configuration such as:

replace it with:

Grails 3 apps by default used Gradle 3.5. Grails 4 apps use Gradle 5.

To upgrade to Gradle 5 execute:

If you customized your app’s build, other migrations may be necessary. Please check Gradle Upgrading your build documentation.

If you were using GORM for Hibernate implementation in your Grails 3 app, you will need to upgrade to Hibernate 5.3.

A Grails 3 build.gradle such as:

will be in Grails 4:

Geb 1.1.x (a JDK 1.7 compatible version) was the version shipped by default with Grails 3. Grails 4 is no longer compatible with Java 1.7. You should migrate to Geb 2.3.

In Grails 3, if your build.gradle looks like:

In Grails 4, you should replace it with:

Create also a Geb Configuration file at src/integration-test/resources/GebConfig.groovy.

GORM 6.1 includes changes that may require you to change your application.

Since Grails 3.3, the Grails Testing Support Framework is used for all unit tests. The new testing framework is much simpler and provides a set of traits that improve readability, debugging and code completion. An example hello world test can be seen below:

For more information on writing tests with Grails Testing Support see the dedicated documentation.

To simplify upgrades you can can still use the previous AST transformation based framework by adding the following dependency to your Grails application:

In previous versions of Grails, if you did not specify a logger in the controller, service, etc, a log variable was injected for you. The naming convention of that logger was grails.app.${artefactType}.package.class. For example:

grails.app.controllers.foo.bar.MyController

To make the logger names more intuitive as well as to increase consistency between custom code, plugin dependencies, and third party libraries, the grails.app.${artefactType} convention was removed. The same class as above will now be referenced the same way as any standard class. The way the log variable gets injected was also changed to defer to the Slf4j transformation. That means it is no longer necessary to check if (log.isDebugEnabled()).

The downside of this change is that it isn’t immediately simple to set up the same logging configuration for all controllers, for example. We think this can be solved with a package naming strategy that represents what your requirements are.

In an effort to trim the size of the produced WAR file by Grails several dependencies are no longer resolved transtively including:

If you are upgrading and have referenced any of these dependencies in your application you may need to alter your build to reference them.

Spring Boot 1.5.x removes a number of deprecated classes, notably all of the classes within the org.springframework.boot.context.embedded package.

If your application is referencing any of the classes within this package you will need to alter your imports to use org.springframework.boot.web.servlet instead.

Since Reactor 2.x is no longer being maintained and a new EventBus abstraction has been implemented, Reactor 2.x and all its dependencies have been removed.

A compatibility layer has been provided to allow classes compiled with the previous version that uses Reactor to run, however all plugins and application code should be re-compiled and direct references to Reactor 2.x should be removed.

Several plugins and libraries have been separated from Grails core into standalone projects. The following table summarizes the previous artefact id, the new artefact id and the location of the new sources:

The Cache plugin has been re-written to no longer use Spring proxies but AST transformations instead.

This improves startup and runtime performance, however one caveat is controller action response caching is no longer supported.

The legacy classes that represent domain classes and their properties have been deprecated in favor of the mapping context API.

The reason for this is to avoid duplicate parsing of the same class data between GORM and Grails and reduce overall startup time.

The internal implementation of the methods in those classes now delegates to the mapping context. Due to that change, information about your domain classes is not available until the application context is available.

In previous versions of Grails it was possible to access GrailsDomainClass instances and inspect the GrailsDomainClassProperty properties inside of the doWithSpring method in a plugin, for example.

If you have code that follows that example, an error will be thrown that looks like "The method …​ cannot be accessed before GORM has initialized". The solution is to move any logic that executes before the context is available to somewhere else that executes after the context is available.

All code that uses the GrailsDomainClass or GrailsDomainClassProperty classes should be re-written to use the mapping context api.

To get started, inject the grailsDomainClassMappingContext bean. See the api documentation for more information on the MappingContext, PersistentEntity (GrailsDomainClass), and PersistentProperty (GrailsDomainClassProperty).

The following table summarizes the deprecations:

The GrailsDomainClassProperty interface had many more methods to evaluate the type of the property such as isOneToOne, isOneToMany etc. and while PersistentProperty does not provide direct equivalents you can use instanceof as a replacement using one of the subclasses found in the org.grails.datastore.mapping.model.types package.

The following table summarizes this:

Grails' previous validation API (part of the grails.validation package) has been externalized into a separate project not part of the grails-datastore-gorm-validation dependency.

This means that some interfaces previously part of Grails core are deprecated and the replacment in the external project should be used, including:

Generally all classes within the org.grails.validation package are now deprecated.

To register a custom constraint you should now use the ConstraintRegistry interface instead.

The default ValidatorRegistry implements the ConstraintRegistry interface and can be autowired into any controller or service by declaring the following property:

The transaction management AST transforms that shipped as part of Grails have been ported to GORM and improved to make it possible to use them outside of Grails.

With this in mind Grails' versions of @Transactional and @Rollback found within the grails.transaction package have been deprecated in favour of GORMs versions. You should change your imports to use the GORM version instead of the Grails version.

The following table summarizes the deprecated classes and their replacements:

Earlier versions of Grails supported the use of Spring proxies for transaction management, but this support was disabled by default in Grails 3.2.x and developers encouraged to use the @Transactional AST transforms instead.

In Grails 3.3 the support for Spring proxies has been dropped completely and you must use Grails' AST transforms.

If you wish to continue to use Spring proxies for transaction management you will have to configure them manually use the appropriate Spring configuration.

In previous versions of Grails and GORM the multiple data sources support relied on Grails' data sources plugin. The logic for configuring multiple data sources has moved to GORM and as a result of major changes to the dataSources plugin, beans for the lazy and unproxied representation of a dataSource are no longer available.

The beans include:

If you are referencing these beans you will need to remove these references and unwrap the single dataSource proxy manually.

Several tasks have had their groups changed to better reflect their purpose. If you’re having trouble finding a task, look through the different groups.

In a previous version of Grails, the JSON builder used by default for rendering JSON inline was changed. The previous behavior of using converters to build the JSON was able to be re-enabled by setting grails.json.legacy.builder to true. In Grails 3.3 that setting has been removed and it is no longer possible to use the legacy converter API to render JSON inline via the render method.

Since the addition of json views, the previous way to convert objects to JSON has been considered legacy. In Grails 3.3 the code to support the legacy converters has been moved out of core and into a separate plugin. That means that by default, code that uses grails.converters.JSON or grails.converters.XML will no longer work by default.

Common usages of this feature are render(book as JSON).

If your codebase uses the legacy converters it is encouraged to convert the functionality to use JSON views, however you can add a dependency in your code to allow current usages of the converters to work again.

The support for rendering with the previous API was disabled by default in 3.1 and was able be re-enabled with the grails.json.legacy.builder: true setting. That setting has been removed in Grails 3.3.

In versions of Grails prior to 3.2, grails.async.Promises used to allow the use of render and other controller methods, however this was unsafe as the request thread may have finished prior to the task executing leading to unexpected errors.

You should now instead use grails.async.web.WebPromises within a controller.

Classes and methods deprecated in Grails 3.0.x have been removed in Grails 3.2. This includes all classes in the org.codehaus.groovy.grails package. If your application or plugin uses deprecated classes they should be updated to use non-deprecated replacements.

The log property injected at compile time into all classes is now an Slf4j Logger instance and not an instance of the Commons Logging Log class.

This should be a simple upgrade for most use cases, however this change does have some implications, for example it is no longer possible to pass non-string types to the log method. Example:

The latter call to the info method will throw an exception as it is not a String.

Instead you should use Slf4j’s formatting anchors to log. The advantage is the toString() method is not called unless the message will be logged.

See the Slf4j FAQ for more information.

Grails 3.2 comes with Spring 4.3 which no longer supports Hibernate 3 and hence Grails 3.2 no longer supports Hibernate 3 either and you will need to upgrade to Hibernate 4 or above.

Spring Boot 1.4, through its dependency management mechanism, enforces the upgrade for many dependencies. You should review your dependencies following the upgrade to ensure the new versions are compatible with your application.

Spring Boot 1.4 also deprecates many testing annotations (such as WebIntegrationTest).

See the Spring Boot 1.4 release notes for more information on the changes required at the Boot level.

Related to Spring Boot 1.4, one important change is that Hibernate 5 is now the default version, so if you have declared a dependency on the hibernate4 plugin in Grails such as:

This will not be enough to ensure that Hibernate 4 is used. You must instead also directly declare the Hibernate 4 dependencies:

In preparation for Hibernate 5.2 support the previous "SessionFactoryBean" notion has been removed. Now if you wish to customize SessionFactory creation you should instead register a custom org.grails.orm.hibernate.connections.HibernateConnectionSourceFactory in Spring.

The grails-datastore-test-support dependency has been removed and the HibernateTestMixin class integrated directly into the plugin, so if you receive a resolve error remove the following dependency from your build.gradle:

An improvement was added to make groovy configuration behave like yml configuration when it comes to the CLI. Previously, configuration values in application.groovy were not available to commands like grails create-controller. A side effect of this change causes an exception when those commands are executed if the configuration relies on classes in the runtime.

The solution is to create a separate file called runtime.groovy in grails-app/conf. That file will not be parsed by the CLI and will only be included at runtime.

Using the default package in places like UrlMappings.groovy, BootStrap.groovy or in a taglib can cause that code to fail or not execute at all when packaged in a JAR or WAR file. Make sure all Groovy/Java files start with the package statement and move any affected files to the respective folder. For example, change:

to:

and move the file from grails-app/controllers/UrlMappings.groovy into .grails-app/controllers/myapp/UrlMappings.groovy

Grails 3.1 ships with GORM 5, which is a near complete rewrite of GORM ontop of Groovy traits and is not binary compatible with the previous version of GORM.

If you receive an error such as:

You are using a plugin or class that was compiled with a previous version of GORM and these will need to be recompiled to be Grails 3.1 and GORM 5 compatible.

For the GORM 5 release the hibernate plugin has been renamed to hibernate4 (and there are hibernate3 and hibernate5 versions too). You should change your build.gradle to reflect that:

The default path for static resources resolved from src/main/resources/public has been changed to be nested under the static/* pattern instead of directly under the root of the application. For example a link in GSP pages such as:

Will produce a URI such as /static/files/mydoc.pdf instead of /files/mydoc.pdf. If you wish to revert to the previous behavior you can configure this in application.yml:

The Filters plugin was replaced by Interceptors in Grails 3.0.x, although the plugin was still present. In Grails 3.1.x the Filters plugin has been removed. If you still wish to use the filters plugin you can add a dependency on the previous version provided by Grails 3.0.x. For example:

You would also need to move the filters to any other source directory (e.g. grails-app/controllers) as grails-app/conf is not considered a source directory anymore.

Because the grails.transactional.Transactional transform already provides the ability to create transactional services without the need for proxies, traditional support for transactional proxies has been disabled by default for new applications.

This means that if you have any services that use the transactional property and not the Transactional annotation they should be altered. For example the following service:

Becomes:

In addition because in previous versions of a Grails transactional defaulted to true any services that do not declare transactional should be altered too.

If you wish to adopt the new behavior then transctional proxies can be disabled with the following configuration:

The default JSON converter no longer includes the class property by default. This can be re-enable with the following configuration:

In addition the default JSON converter will no longer render the id property if it is null.

The class grails.web.JSONBuilder has been deprecated and replaced with groovy.json.StreamingJsonBuilder, the default JSON builder within Groovy. This avoids confusion with the differences between JSON builders and better aligns with Groovy’s core libraries.

This also means that any render blocks that rendered JSON will need to be updated to use the groovy.json.StreamingJsonBuilder syntax. For example the following code:

Should instead be written as:

If you are upgrading and prefer to continue to use the previous implementation then you can re-enable the deprecated JSONBuilder with the following configuration:

With the addition of JSON views the previous API for using JSON converters is largely discouraged in favour of views. The converters plugin will in the future be separated into an external plugin and JSON views phased in to replace it. The JSON converter API is not deprecated, however JSON views provide a more fully featured, elegant API that is superior to writing JSON converters and/or marshallers.

Grails 3.1 ships with upgraded third party libraries that may require changes. See the Spring Boot upgrade notes for information.

Unlike Spring Boot 1.2, Spring Boot 1.3 no longer uses the Gradle Application Plugin so if you relied on any behavior the application plugin then the plugin will need to be re-applied to your build.gradle.

Spring Boot 1.3 also uses Spring Security 4.x by default, so if you project depends on Spring Security 3.x you have to force a downgrade. For example:

Because the Gradle run task for application startup was provided by the Gradle Application Plugin (see above), it is no longer available by default. If you use Gradle to start up your application, use the bootRun task instead, or re-apply the Application plugin in your build.gradle.

Note: If you don’t have need of the Gradle Application plugin’s features, but have custom Gradle tasks or IDE configurations that depend on run, you can supply your own run task that depends on bootRun in your build.gradle:

The Resource annotation applied to domain classes defaults to XML in Grails 3.0.x, but in Grails 3.1.x and above it defaults to JSON.

If you use this annotation with the expecation of produces XML responses as the default you can modify the definition as follows:

This will restore the Grails 3.0.x behavior.

If you use Geb with HTMLUnit (something that is not recommended, as a more native driver such as PhantomJS is recommended) you will need to upgrade your dependencies in build.grade:

Note that there are also some changes in behavior in HTMLUnit 2.18 that may cause issues in existing tests including:

An improvement was added to make groovy configuration behave like yml configuration when it comes to the CLI. Previously, configuration values in application.groovy were not available to commands like grails create-controller. A side effect of this change causes an exception when those commands are executed if the configuration relies on classes in the runtime.

The solution is to create a separate file called runtime.groovy in grails-app/conf. That file will not be parsed by the CLI and will only be included at runtime.

Before and after interceptors were removed. So all beforeInterceptor and afterInterceptor need to be replaced by Stand alone interceptors.

The first step is to create a new Grails 3 plugin using the command line:

This will create a Grails 3 plugin in the quartz directory.

The next step is to copy the sources from the original Grails 2 plugin to the Grails 3 plugin:

You will need to add a package declaration to the plugin descriptor. In this case QuartzGrailsPlugin is modified as follows:

In addition you should remove the version property from the descriptor as this is now defined in build.gradle.

The repositories and dependencies defined in grails-app/conf/BuildConfig.groovy of the original Grails 2.x plugin will need to be defined in build.gradle of the new Grails 3.x plugin:

It is recommended to use the latest stable, Grails 3+ compatible version of plugins. (Grails 2.x plugin versions will not work.)

In Grails 3.x all internal APIs can be found in the org.grails package and public facing APIs in the grails package. The org.codehaus.groovy.grails package no longer exists.

All package declaration in sources should be modified for the new location of the respective classes. Example org.codehaus.groovy.grails.commons.GrailsApplication is now grails.core.GrailsApplication.

Some plugins define a default configuration file. For example the Quartz plugin defines a file called grails-app/conf/DefaultQuartzConfig.groovy. In Grails 3.x this default configuration can be migrated to grails-app/conf/application.yml and it will automatically be loaded by Grails without requiring manual configuration merging.

Old plugins may have a pluginExcludes property defined that lists the patterns for any files that should not be included in the plugin package. This is normally used to exclude artifacts such as domain classes that are used in the plugin’s integration tests. You generally don’t want these polluting the target application.

This property is no longer sufficient in Grails 3, and nor can you use source paths. Instead, you must specify patterns that match the paths of the compiled classes. For example, imagine you have some test domain classes in the grails-app/domain/plugin/tests directory. You should first change the pluginExcludes value to

and then add this block to the build file:

The easiest way to ensure these patterns work effectively is to put all your non-packaged class into a distinct Java package so that there is a clean separation between the main plugin classes and the rest.

In Grails 3.x ArtefactHandler definitions written in Java need to be declared in a file called src/main/resources/META-INF/grails.factories since these need to be known at compile time.

The Quartz plugin requires the following definition to register the ArtrefactHandler:

Many plugins previously defined command line scripts in Gant. In Grails 3.x command line scripts have been replaced by two new features: Code generation scripts and Gradle tasks.

If your script is doing simple code generation then for many cases a code generation script can replace an old Gant script.

The create-job script provided by the Quartz plugin in Grails 2.x was defined in scripts/CreateJob.groovy as:

A replacement Grails 3.x compatible script can be created using the create-script command:

Which creates a new script called src/main/scripts/create-job.groovy. Using the new code generation API it is simple to implement:

Please refer to the documentation on Creating Custom Scripts for more information.

Using the old Grails 2.x build system it was relatively common to spin up Grails inside the command line. In Grails 3.x it is not possible to load a Grails application within a code generation script created by the create-script command.

Instead a new mechanism specific to plugins exists via the create-command command. The create-command command will create a new ApplicationCommand, for example the following command will execute a query:

With this command in place once the plugin is installed into your local Maven cache you can add the plugin to both the build classpath and the runtime classpath of the application’s build.gradle file:

Grails will automatically create a Gradle task called runQuery and a command named run-query so both the following examples will execute the command:

You should now delete and cleanup the project of any files no longer required by Grails 3.x (BuildConfig.groovy, Config.groovy, DataSource.groovy etc.)

Once the plugins are Grails 3.x compatible you can upgrade the application. To upgrade an application it is again best to create a new Grails 3 application using the "web" profile:

The next step is to copy the sources from the original Grails 2 application to the Grails 3 application:

The repositories and dependencies defined in grails-app/conf/BuildConfig.groovy of the original Grails 2.x application will need to be defined in build.gradle of the new Grails 3.x application.

In Grails 3.x all internal APIs can be found in the org.grails package and public facing APIs in the grails package. The org.codehaus.groovy.grails package no longer exists.

All package declaration in sources should be modified for the new location of the respective classes. Example org.codehaus.groovy.grails.commons.GrailsApplication is now grails.core.GrailsApplication.

The configuration of the application will need to be migrated, this can normally be done by simply renaming grails-app/conf/Config.groovy to grails-app/conf/application.groovy and merging the content of grails-app/conf/DataSource.groovy into grails-app/conf/application.groovy.

Note however that Log4j has been replaced by grails-app/conf/logback.groovy for logging, so any logging configuration in grails-app/conf/Config.groovy should be migrated to logback format.

If you have a modified web.xml template then you will need to migrate this to Spring as Grails 3.x does not use a web.xml (although it is still possible to have on in src/main/webapp/WEB-INF/web.xml).

New servlets and filters can be registered as Spring beans or with ServletRegistrationBean and FilterRegistrationBean respectively.

If you have static assets in your web-app directory of your Grails 2.x application such as HTML files, TLDs etc. these need to be moved. For public assets such as static HTML pages and so on these should go in src/main/resources/public.

TLD descriptors and non public assets should go in src/main/resources/WEB-INF.

As noted earlier, src/main/webapp folder can also be used for this purpose but it is not recommended.

Once the package names are corrected unit tests will continue to run, however any tests that extend the deprecated and removed JUnit 3 hierarchy will need to be migrated to Spock or JUnit 4.

Integration tests will need to be annotated with the Integration annotation and should not extend GroovyTestCase or any JUnit 3 super class.

The Constraints section of a Domain Class (or other validateable object) looks like this:

In Grails 2.x, fields with no constraints could be declared in the Constraints block, as a method call with no arguments. Example (NB. the following syntax is no longer supported):

A different syntax has to be used in Grails 3. Either remove the field declaration from the constraints block (if there are no constraints to specify for it), or to keep the field placeholder, pass an empty map argument: \[:\] instead of ().

Replacement code for Grails 3.x:

If such declarations have not yet been changed then a log message like this emits on startup:

If your project had inline plugins in Grails 2.x, contains ASTs, or if your project is composed of several modules or related applications then you may decide to restructure your project as a Gradle multi-project build.

Sample multi-project structure:

How to configure this is documented in the Plugins section under the heading 'Inline Plugins in Grails 3.0'.

During the progress of migrating code from Grails 2.4 to Grails 3.1+, your project (and the plugins that your project depends on) will be moving to GORM 5 (or higher) and other newer library versions. You might also wish to familiarise yourself with the differences mentioned in the section Upgrading from Grails 3.0.

If your application contains AST transformations, please be aware that for these to be applied to your application code, they must now be contained within a plugin. (In Grails 2.x it was possible to pre-compile AST transformations then apply them to your application code by hooking into compile events in _Events.groovy. This is no longer possible. Move your AST Transformation classes and associated annotations into a plugin for this purpose.)

There are two AST patterns on which you can base migration of your AST transformer code:

Grails uses Spring Boot to embed a Tomcat or Jetty instance by default. To build a war file for deployment to a container you will need to make a simple change to build.gradle (so that a container is not embedded).

If you deploy to a Tomcat 7 container then there is an additional step. Grails 3 is built against Tomcat 8 APIs by default. You will need to change the target Tomcat version in the build to 7.

There are standalone deployment options available.

Refer to the Deployment guide for further details.

If your application uses multiple datasources, then be aware that the way these are declared in application.yml or application.groovy (previously DataSources.groovy) has changed.

If there is more than one DataSource in an application there is now a dataSources { …​ } configuration block to contain them all. Previously, multiple dataSource declarations were used, with an underscore and suffix on the additional datasources, e.g. dataSource_lookup { …​ }.

Please refer to the user guide section on Multiple Datasources for examples.

In your Grails 2.x app you may have used Spring @Autowired in a few situations, such as dependency injection into certain base classes, and for typed field dependency injection. For example:

Grails now has support for dependency injection into typed fields in addition to untyped def fields, following the usual Grails conventions of field name matching the bean property name. Example:

You may find that @Autowired no longer works as it did previously in your code on artefacts or base classes, in certain scenarios, resulting in NULL for these fields. Changing these to a simple typed Grails dependency following the Grails naming convention and removing @Autowired should resolve this.