I use JBoss 5.1 but I think you have to consider the following points:
1. Complexe classes as a return type must implement java.io.Serializable
2. If you want to return lists, then change the return type to an array and convert the list with a statement like this:
SomeObject[] arr = (SomeObject[]) list
.toArray(new SomeObject[list.size()]);
In eclipse you will retrieve a pattern for this command with 'toarray'
And Overloading is unfortunately not allowed.
Hope it helps.