I am in the planning stages of a specific subject matter community web site, and one feature I feel is required is that of member discussions. However, not in a typical forum style. For example, I don't want the members to have to navigate away from their own "user space" in order to discuss a topic.

I think it is best described with an analogous example. Lets say the site is for literature buffs, and each member has a set of pages for keeping notes, progress, questions, etc. on books they are studying/reading. So Joe will have one page for Great Expectations, another for Hamlet, a third for I, Robot, and so forth. Likewise, Jane will have a page for Don Quixote, Lord of the Flies, and also I, Robot. Now, wouldn't it be nice if Joe and Jane could discuss I, Robot from within their own respective pages?

Now, at first thought, roll your own seems like the way to go. However, once we start getting into issues such as spam blocking, banning, ratings, pruning, archiving, flooding and so on, well "roll your own" doesn't sound too appealing anymore. Also, I have next to zero experience with forum software.

So I'm looking for forum software that has an extensive API or is generally very integration-friendly. I would like to be able to create user groups, topics, permissions, etc. programmatically,as well as the obvious user authentication (most seem open in that respect).

The site will most probably be built with Java.

Tangler seems like a descent option, but it seems less mature than what I'd prefer.