JAXB marshalling purely from interfaces

Question

I have a complex hierarchy of Java interfaces that I\'d like to marshal (and not necessarily unmarshal) with JAXB. These interfaces represent objects that will be returned from

Answer 1

I think the answer is that JAXB isn't at all intended to support this and that it's foolish to try to force it. Also, JAXB-driven JSON marshaling turns out not to be ideal either.

I ended up writing my own marshaling framework, with its own set of annotations:

@MarshalMixin // marshal fields but not a top-level object
interface Uuided {
  @MarshalAsString // ignore properties; just call toString()
  @MarshalId // treat as identifier for @MarshalUsingIds or cyclic ref
  UUID getId();
}
@MarshalMixin
interface Named {
  @MarshalId
  String getName();
}
@MarshalObject // top-level marshaled object providing class name
interface Component extends Uuided, Named {
  @MarshalAsKeyedObjectMap(key = "name") // see description below
  Map getAttributes();
}
@MarshalObject
interface Attribute extends Named {
  Type getType();
  @MarshalDynamic // use run-time (not declared) type
  Object getValue();
}
interface ComponentAttribute extends Attribute {
  @MarshalUsingIds
  Component getDeclaringComponent();
}

The generated marshalers write to an abstraction layer (currently implemented for JSON and XML). This gives a lot more flexibility to make the output natural for different representations without a ton of annotations and adapters. E.g., what I'm calling keyed-object maps, where each object contains its map key. In JSON, you want a map, but in XML, you want a sequence:

{..., map: {'a': {'name': 'a', ...}, 'b': {'name: 'b', ...}, ...}, ...}
......

Seems like as many as 4 other people care about this too, so hopefully I can open-source it eventually. :-)