[Java] Using a complex datastructure as Key for KV

[Shannon Duncan]

So I'm working on essentially doing a word-count on a complex data
structure.

I tried just using a HashMap as the Structure, but that didn't work because
it is non-deterministic.

However when Given a LinkedHashMap or TreeMap which is deterministic the
SDK complains that it's non-deterministic when trying to use it as a key
for GroupByKey.

What would be an appropriate Map style data structure that would be
deterministic enough for Apache Beam to accept it as a key?

Thanks,
Shannon