There are over 100 web frameworks for Java; a veritable mixing bowl. Each framework has it's merits and backers. So why do we need more? Good question. In my humble opinion, AJAX is the killer app of web development, and a growing legion of companies and developers invest time and money in the AJAX space.
jLynx, a simple ORM framework, has incorporated a simple 2-class framework into Version 1.5 (release May 2, 2008). The concept is to provide a web filter that binds request parameters to a POJO. A handler defines methods to respond to the request. The HttpServletRequest and HttpServletResponse objects are available to the developer as well as the POJO bound to the request. The response is sent via the sendResponse(String) method.
If you love AJAX check out this framework. Of course we can always add functionality, but the objective is to keep it simple.
To learn more, see the wiki at the: jLynx Google Code site.