Marshalling nested classes with JAXB

Question

I am trying to marshal some classes I designed, with standard JAXB, the classes all have void constructors, this is my first attempt at using JAXB or marshalling/unmarhslling in any language for that matter but as I understand it JAXB should be able to marshall them without a XSD.

The classes are as follow:

@XmlRootElement(name="place")
class Place {
    @XmlAttribute
    //various fields and get set methods
    public Place() {          
    }
}

@XmlRootElement(name="Arc")
class Arc {
    // various fields and get set methods
    @XmlAttribute
    Place p;
    public setPlace(Place p) {
        // ...
    }

    public Arc() { 
    }
}

@XmlRootElement(name="Transition")
class Transition {
   Arc[] a;

   public Transition() {        
   }
}

I can marshall the Place class but not the Arc class, the Transition I didn't even try, the classes have the @XMLPropriety tags but when it reaches the nested Place class JAXB doesn't seem to understand which XML object to map it too.

If there is another tag I should be using for the nested class or there's another error I'm overlooking?

Answer 1

There is nothing special you need to do to handle nested classes with any JAXB (JSR-222) implementation. Below is a complete example where only one @XmlRootElement annotation is used:

Transition

package forum13159089;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
class Transition {

    Arc[] a;

    public Arc[] getA() {
        return a;
    }

    public void setA(Arc[] a) {
        this.a = a;
    }

}

Arc

package forum13159089;

class Arc {

    Place p;

    public Place getPlace() {
        return p;
    }

    public void setPlace(Place p) {
        this.p = p;
    }

}

Place

package forum13159089;

class Place {

}

Demo

package forum13159089;

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Transition.class);
        
        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum13159089/input.xml");
        Transition transition = (Transition) unmarshaller.unmarshal(xml);
        
        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(transition, System.out);
    }

}

input.xml/Output

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<transition>
    <a>
        <place/>
    </a>
    <a>
        <place/>
    </a>
</transition>

For More Information

• http://blog.bdoughan.com/2012/07/jaxb-no-annotations-required.html
• http://blog.bdoughan.com/2010/09/jaxb-collection-properties.html
• http://wiki.eclipse.org/EclipseLink/Examples/MOXy/GettingStarted

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Note: @XMLProperty is not a JAXB annotation.