I want to generate a RSS feed that can be displayed threaded in RSS-Clients.
So if the feed describes something like comments or changes to one and the same entity, i want these to be visually grouped.
Is this possible in Java?
There are ATOM Threading Extensions that will do the job. Atom Feeds will be displayed threaded in Thunderbird / Outlook when those are used.
They should be pretty simple to implement for any RSS-Library. For rome i published a rome-module that can be used.