Objects to XML

Question

I use XStream to parse the following Objects to XML, the problem is what to do with:
class Tag {
@XStreamAsAttribute
List<SubTag1> st1 = new ArrayList<SubTag1>();
@XStreamAsAttribute
List<SubTag2> st2 = new ArrayList<SubTag2>();
...When the class Tag is converted to XML it will always contain both a 'st1' and 'st2' even when I only
have a Tag that ONLY contains 'st1'.
Tag should be able to contain:
1) List of SubTag1
or
2) List of SubTag2
or
3) List of SubTag1 and List of SubTag2
How do I make sure to only process the Lists if they contains elements?

Answer 1

Looks like you need a converter, for more info you could try the [XStream mailing list|http://xstream.codehaus.org/list-user.html].