How do I get Groovy and JAXB to play nice together

Question

I am trying to get JAXB to work with a groovy class of mine, however, it appears it doesn't work but the java version does. Here is the code...

Here are the Scenarios:

If 2 and 3 are uncommented it works fine.

If 1 and 4 are uncommented I get:

 com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException:
       2 counts of IllegalAnnotationExceptions
 groovy.lang.MetaClass is an interface, and JAXB can't handle interfaces.

If 1 and 5 are uncommented I get:

  javax.xml.bind.JAXBException: class org.oclc.presentations.simplejaxb.PlayerGroovy
        nor any of its super class is known to this context.

Any ideas?

Java:

    import javax.xml.bind.annotation.XmlRootElement;

    @XmlRootElement
    public class Player {
    }

Groovy:

    import javax.xml.bind.annotation.XmlRootElement

    @XmlRootElement
    public class PlayerGroovy {
    }

Test:

    import org.junit.Test
    import javax.xml.bind.JAXBContext
    import javax.xml.bind.Marshaller
    import org.junit.Assert

    class PlayerTest {
        @Test
        public void testJaXB(){
            //1 PlayerGroovy player = new PlayerGroovy()
            //2 Player player = new Player()
            StringWriter writer = new StringWriter();
            //3 JAXBContext context = JAXBContext.newInstance(Player.class);
            //4 JAXBContext context = JAXBContext.newInstance(PlayerGroovy.class);
            //5 JAXBContext context = JAXBContext.newInstance(PlayerGroovy.getClass());
            Marshaller m = context.createMarshaller();
            m.marshal(player, writer);
            println(writer)
            Assert.assertTrue(true)
        }
    }

Answer 1

I was having the same problem while exposing a Grails GORM object. After researching the solution posted above, using @XmlAccessorType( XmlAccessType.NONE ), I quickly grew tired of marking everything as @XmlAttribute.

I'm having plenty of success using:

@XmlAccessorType( XmlAccessType.FIELD )
@XmlRootElement
public class PlayerGroovy {
    String value
}

See: XmlAccessType

Thanks to the original answer for getting me started in the right direction.

Answer 2

The solution does not seem to work on an abstract subclass. I think it's because the compiler does not generate the getMetaClass override code. I ended up mimicking the steps from this question as follows:

@XmlAccessorType(XmlAccessType.NONE)
package groovy.lang;

import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;

Yes, it's kinda weird. In my case, I have code like this:

package pkg;
abstract class ScriptMomma extends groovy.lang.Script {
    // write some nice supporting code here
}

And to execute my scripts, I have:

def config = new org.codehaus.groovy.control.CompilerConfiguration()
config.scriptBaseClass = 'pkg.ScriptMomma'
ScriptMomma mine = new GroovyShell(config).evaluate(scriptFile, 'TheOne')

I'd prefer a better solution, but right now this is all I have.

Answer 3

Uncommenting 1 and 4 is the correct way to set JAXB up with Groovy. The reason it is not working is that each Groovy Class has a metaClass property on it. JAXB is trying to expose this as a JAXB property which obviously fails. Since you don't declare the metaClass property yourself, it is not possible to annotate it to have JAXB ignore it. Instead you and set the XmlAccessType to NONE. This disable's JAXB's auto-discovery of properties to expose as XML elements. After you do that, you need to explicitly declare any fields you want exposed.

Example:

@XmlAccessorType( XmlAccessType.NONE )
@XmlRootElement
public class PlayerGroovy {
    @XmlAttribute
    String value
}