Grails - XML Conversion

Grails provides some effortless features for converting objects into XML, but some care is necessary when using them.

By default, the XML representation of an object is shallow - this means any reference to another domain object will be represented by the id in the xml document. If the xml document should contain the full object tree, a flag in the converter needs to be set.

Adding the following line to Config.groovy will set the default for the system

grails.converters.xml.default.deep = true

or if you prefer, you can do the same thing programatically

grails.converters.XML.use('deep')

in either case, you can test it out with the following code

def converter = new grails.converters.XML(myInstance)
converter.render(new java.io.FileWriter("c:\\output.xml"))
// or
def xmlStr = myInstance as XML

One issue we had with deep converters was that it was including too much information - our User domain class contained a (cleartext) password field which was being displayed in the resulting xml.

We can customize the behavior for transforming an object into xml by using the registerObjectMarshaller method. This method is passed a class name and a closure which handles writing the XML output. The closure has implicit access to both the instance of the encountered class and the converter used to transform it.

class User {
   String login
   String name
   String password
}

def converter = new XML(aUser)
converter.registerObjectMarshaller(User, {user, conv ->
   conv.build {
       login(user.login)
       name(user.name)
   }
})

or you could set the converter for the entire system by putting the same code in Bootstrap.groovy

grails.converters.XML.registerObjectMarshaller(User) { user, converter ->
   // same implementation as above...
}