Using JAXB annotations, how do you get each XML element of a list wrapped in an element, when each list element has an unknown name?

Question

How is this XML structure modeled in a JAXB class annotation?

<root>
 <linksCollection>
  <links>
    <foo href="http://example.com/foo" rel="link"/>
  </links>
  <links>
    <bar href="http://example.com/bar" rel="link"/>
  </links>
 </linksCollection>
</root>

Starting with the following root class, what is the Link class? How do you get each link with an unknown element name to be wrapped in the links element?

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Root {

    @XmlElement
    protected List<Link> linksCollection;
    // etc.
}

The following attempt does not work:

@XmlRootElement(name = "links")
@XmlAccessorType(XmlAccessType.FIELD)
public class Link {

    @XmlAnyElement
    protected Object link;
    @XmlAttribute
    protected String href;
    @XmlAttribute
    protected String rel;
    //etc.
}

Answer 1

Your attempt with @XmlAnyElement for the unknown elements is the right way, but you were missing the @XmlElementWrapper for the collection. The following mapping produces a collection for those elements:

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Root {

    @XmlElementWrapper(name="linksCollection")
    @XmlElement(name="links")
    protected List<Link> linksCollection;

}

public class Link {

    @XmlAnyElement(lax = true)
    protected Object content;

}

According to this explanation you will have an instance of org.w3c.dom.Element in your collection if you do not specify a mapping.

If you have only a limited subset of unknown elements, you could change the annotation in the link class as follows:

@XmlElements({
    @XmlElement(name = "foo", type = FooBar.class),
    @XmlElement(name = "bar", type = FooBar.class) , ...})
protected Object content;

The FooBar class could then look like this:

public class FooBar {

    @XmlAttribute(name = "href")
    protected String href;

    @XmlAttribute(name = "rel")
    protected String rel;

}

However when you can't predict the possible tags, I would stay with the @XmlAnyElement and add a @XmlTypeAdapter . There is another thread: Jaxb complex xml unmarshall about this topic.