As a suggestion... you can skip HQL validation by adding an intermediate function called "unionQuery", the suggested sintax would be like this:

Query q = session.createQuery(HQL1).unionQuery(HQL2).unionQuery(HQL3);

That way you can reuse the same HQL validation and the only left thing to do is to validate each query returned values/types;

I fixed this for my requirement by now doing the following (i'm simplifying a lot this example, is only to give you the idea):

List q = new ArrayList();
q.add("HQL1");
q.add("HQL2");
q.add("HQL3");
List result = null;
for(String hql : q) {
if(result == null)

else

}