Unmarshal generates null field on generic with a List<T> field

I have a Web Service created in Java (1.6), with metro (2.0), using maven, under Tomcat 6. In all web methods the return type is a generic class:

public class WsResult<T> {
    protected T result;          // the actual result
    protected Code requestState; // 0K, or some error code if needed
    protected String message;    // if error, instead of result, insert a message
}

For example:

public WsResult<OtherClass> someMethod(...);
public WsResult<Foo> someMet开发者_运维问答hod_2(...);

And in client:

MyServiceService service = new MyServiceService();
MyService port = service.getMyServicePort();

WsResult result = port.someMethod(...);
OtherClass oc = (OtherClass) result.getResult();

WsResult res = port.someMethod_2(...);
Foo o = (Foo) res.getResult();

In some web methods it is working. But when the result is a class with have a List<? class> attribute, it fails to unmarshal.

This project is part of a biggest one. So for test purposes I created a new one, simpler, just the project, with the same data model, and copy one of the web methods, in this case it worked, and after unmarshal, I had a result that i could cast to the expected type.

What could be happening?

EDIT:

The answer is a solution yes, but generates a getter for each type added to the field declaration. Is there a better way?

I'm not really sure if I fully understand your problem, but to me it seems you expect a little too much from JAXB here. Your WsResult is generic in the unrestricted parameter T, which means at runtime there's nothing left but an Object reference for JAXB to play with.

What JAXB really needs to deal with such a situation is, loosely speaking, a hint on which class to instantiate to fill the result field. To fill this in you should either

• create concrete subclasses of WsResult (like, following your example, class OtherClassResult extends WsResult<OtherClass> -- when you throw the OtherClassResult at JAXB, it will know that result needs to be an instance of OtherClass and has a chance to act accordingly or
• annotate the result field with @XmlElements, like this:

@XmlElements({
    @XmlElement(name = "text", type = String.class), // add more elems here
    @XmlElement(name = "other", type = OtherClass.class)})
protected Object result;