Direct Web Remoting(DWR), you don't have to. Joe Walker shows how this java.net project provides solutions for developing both the server- and client-side pieces of an AJAX web application.
rating comment: The article gives a straight high level overview of Direct Web Remoting. Since it's on java.net, I would have expected a little more technical details, like what's going on behind the scenes. But if you don't have any experience with AJAX or Direct Web Remoting at all, it's a nice introduction.
I dug a little deeper and I must say I am quite impressed of Direct Web Remoting. It really makes it easy to develop AJAX web sites, and I definitely gotta check it out! The most impressive thing is, how easy it is to fill data into HTML components, using the util functions. It's really helpful and saves a lot of time and work!