Grails Goodness: Customize Root Element Name Collections for XML Marshalling
When we convert a List
or Set
to XML using the Grails XML marshalling support the name of the root element is either <list>
or <set>
. We can change this name by extending the org.codehaus.groovy.grails.web.converters.marshaller. xml.CollectionMarshaller
. We must override the method supports()
to denote the type of collection we want to customize the root element name for. And we must override the method getElementName()
which returns the actual name of the root element for the List
or Set
.
Let’s first see the default output of a collection of Book
domain classes. In a controller we have the following code:
package com.mrhaki.grails.sample class SampleController { def list() { // To force 404 when no results are found // we must return null, because respond method // checks explicitly for null value and // not Groovy truth. respond Book.list() } }
The XML output is:
<?xml version="1.0" encoding="UTF-8"?> <list> <book id="1" version="0"> <author id="1" /> <isbn> 0451169514 </isbn> <numberOfPages> 1104 </numberOfPages> <title> It </title> </book> <book id="2" version="0"> <author id="1" /> <isbn> 0307743683 </isbn> <numberOfPages> 1472 </numberOfPages> <title> The stand </title> </book> </list>
To change the element name list
to books
we add the following code to the init
closure in grails-app/app/BootStrap.groovy
:
// File: grails-app/conf/BootStrap.groovy import com.mrhaki.grails.sample.Book import grails.converters.XML import org.codehaus.groovy.grails.web.converters.marshaller.xml.CollectionMarshaller class BootStrap { def init = { servletContext -> // Register custom collection marshaller for List with Book instances. // The root element name is set to books. XML.registerObjectMarshaller(new CollectionMarshaller() { @Override public boolean supports(Object object) { // We know there is at least one result, // otherwise the controller respond method // would have returned a 404 response code. object instance of List && object.first() instance of Book } @Override String getElementName(final Object o) { 'books' } }) } }
Now when we render a list of Book
instances we get the following XML:
<?xml version="1.0" encoding="UTF-8"?> <books> <book id="1" version="0"> <author id="1" /> <isbn> 0451169514 </isbn> <numberOfPages> 1104 </numberOfPages> <title> It </title> </book> <book id="2" version="0"> <author id="1" /> <isbn> 0307743683 </isbn> <numberOfPages> 1472 </numberOfPages> <title> The stand </title> </book> </books>
To customize the XML marshaling output for Map
collections we must subclass org.codehaus.groovy.grails.web.converters.marshaller.xml.MapMarshaller
.
Code written with Grails 2.3.2.