Whatever solution you may eventually go with one thing is certain - it wont be based on Client Side Scripting. Although it could play a part.
I guess your next best option is to use a server side technology such as PHP. This will of course involve making repeated checks to the server every, say, 5 seconds to see if a new post has been made, but if Java isn't an option then that can't be helped.
Before I go any further what do you have available to you?