Is it possible to ignore a wrapper class during JAXB marshalling

Question

I'm trying to get JAXB to ignore a wrapper class during the Mashalling process, it makes sense to have this wrapper class in code, as it keep all related information together, however I need to get rid of it during the marshaling process. The following is the relevant code.

@XmlType(name = "root")
@XmlRootElement(name = "root")
public class Root {

    @XmlElementRef
    private List<Resource> resources = new ArrayList<>();

    public void addResource(Resource resource) {
        resources.add(resource);
    }
}


@XmlRootElement(name = "", namespace = "")
@XmlAccessorType(XmlAccessType.NONE)
public class Resource {

    @XmlElementRef
    private Element element;
    @XmlElementRef
    private FieldType fieldType;
    @XmlElementRef
    private ListType listType;
}

Root is the main object, and Resource is the wrapper object that I'd like not have a node created for. I still want the Element, FieldType and ListType within the Resource to be rendered however.

This is what I currently have:

<root>
    <>
        <element name="resource1"/>
        <fieldType name="resource1--type">
        </fieldType>
        <listType name="resource--list">
        </listType>
    </>
    <>
        <element name="resource2"/>
        <fieldType name="resource2--type">
        </fieldType>
        <listType name="resource2--list">
        </listType>
    </>
</root>

What I'd like to achieve is the following:

<root>
    <element name="resource1"/>
    <fieldType name="resource1--type">
    </fieldType>
    <listType name="resource--list">
    </listType>
    <element name="resource2"/>
    <fieldType name="resource2--type">
    </fieldType>
    <listType name="resource2--list">
    </listType>
</root>

I don't know if it's possible, but any help would be appreciated.

Thanks.

Answer 1

You cannot achieve that in JAXB. Even if you would be able to serialize like this, using a XmlAdapter for example, it will be impossible to deserialize it.

Try this:

@XmlType(name = "root")
@XmlRootElement(name = "root")
@XmlAccessorType(XmlAccessType.NONE)
public class Root {

    private ArrayList<Resource> resources = new ArrayList<Resource>();

    public void addResource(Resource resource) {
        resources.add(resource);
    }

    @XmlElementRefs(value = { @XmlElementRef(type = Element.class),
                              @XmlElementRef(type = ListType.class),
                              @XmlElementRef(type = FieldType.class) })
    public List<Object> getResourceFields() {
        List<Object> list = new ArrayList<Object>();
        for (Resource r : resources) {
            list.add(r.getElement());
            list.add(r.getFieldType());
            list.add(r.getListType());
        }
        return list;
    }
}

Basically getRerourceFields concatenates all the resources' fields in the same list. If you cannot change the Root class, this could be your RootAdapter and use it as @Biju suggested.

Answer 2

You probably will have to create an XmlAdapter for your Root class, this adapter should basically map your root instances to a different type, where you can flatten your root structure before marshalling - along these lines:

public class CustomRootAdapter extends
                    XmlAdapter<CustomRoot,Root>> {
@Override
public Root unmarshal(CustomRoot v) throws Exception {
    return null;//if you are not keen on unmarshalling..
}
@Override
public CustomRoot marshal(Root v) throws Exception {
    return ...;
}    

}

You can register this Custom adapter using:

@XmlJavaTypeAdapter(CustomRootAdapter.class) with your Root class