The RXTXComm library works just fine. I used is just recently and I got bidirecional communication between my Java program and my arduino board. There are a few thing to watch out for, but i will not post because the author of the thread seems to have got what he wants and the post would be rather long to write. Besides, i just joined this forum, but i am sure there must be a working example here on using RXTXComm jar.
If someone is interested, i will post the info thou ...