If you wanna create community/forum for sake of getting hands on JAVA then I would say, yes you can do it with Java, and one of the combinations which you might want to use for it can be:
above are some very simple and commonly used technologies. So I would say go for them.
But let me tell you my friend, for creating something par excellence, a few thumb rules:
1. Don't be technology specific, just use what's most suitable (To find what's most suitable is most exciting thing in a devloper's life).
2. Try to create as much reusable components as u can.
3. Design your application in multi-tier model. That would certainly help you and other people in maintenance phase.
So, good luck with JAVA, develop something good, and let us have the URL :)