(Quick Reference)
withFormat
Purpose
Renders different responses based on the incoming request
Accept header, format parameter or URI extension. See
content negotiation for more information.
Examples
import grails.converters.XMLclass BookController { def list() {
def books = Book.list() withFormat {
html bookList:books
js { render "alert('hello')" }
xml { render books as XML }
}
}
}Description
The
withFormat accepts a Closure which contains methods corresponding to the different content types you want to respond to. For example:
withFormat {
html bookList: books
js { render "alert('hello')" }
xml { render books as XML }
}Here we invoke three methods called
html,
js and
xml that use mime type names configured in
grails-app/conf/application.groovy (See
content negotiation for more information). The call to
html accepts a model (a Map) which is passed on to the view. Grails searches for a view called
grails-app/views/book/list.html.gsp and if that is not found fallback to
grails-app/views/book/list.gsp.
Note that the order of the types is significant if the request format is "all" or if more than one content type has the same "q" rating in the accept header. In the former case, the first type handler in the block is executed ("html" in the short example above). The latter case is more confusing because it only holds if there is more than one content type with the highest "q" rating for which you have a type handler
and you have more than one type handler matching that "q" rating. For example if the request has "text/html" and "application/xml" with a "q" rating of 1.0, then this code:
withFormat {
xml { … }
html { … }
}will use the "xml" type handler for the request.
Another important factor to note is that the
withFormat method deals with the
response format and not the request format. As of Grails 2.0, there is a separate
withFormat method made available on the
request that you can use to handle the request format which is dictated by the
CONTENT_TYPE header of the request:
request.withFormat {
form { .. }
xml { .. }
json { .. }
}
The request format of form is used for handling form submission in content negotiation as opposed to html.
If you require that the model be lazily executed you can pass a Closure instead of a Map:
withFormat {
html { [bookList: Book.list()] }
…
}This way the
html Closure will only be executed if the
html format is matched.
Grails ignores the HTTP Accept header unless you add a grails.mime.use.accept.header = true setting to your application.groovy file. In other words, withFormat() will be completely unaffected by the Accept header without that setting.
