JSP/J2EE is used for several reasons that I won't get into:)
However creating a widget requires only Javascript.
Actually I was looking to build a collab whiteboard app myself some time ago, but then I decided to focus only on one, the one I am currently building. I explored what is out there at that point of time and I found quite a few, a few good one's will be http://www.jotspace.com/, http://www.instructure.com/ [not a whiteboard, more of other collab features], http://etherpad.com/. Check them out. That interest was the reason why went ahead and explored it. The UI is prototypical, needs a lot of work.
I will play with it sometime when I get time.
Keep up the good work.