This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
The HTTP requests from the clients at server are intercepted by the HTTP listners and then sent for further request processing.You can write your own HTTP listner and install at tomcat (defualt is coyote listner).
Note this answer is specific to tomcat and if you can change the tomcat settings.