Java EE (Java Enterprise Edition) General Discussion

I have a web appliaction with the server running as a servlet using Tomcat. The client is a applet or javascript-html based thin client. When I launch a request to the server sometimes it takes too long to process because the server spawns new threads and connects to databases, gets data and processes them before sending the response back. Now if the user closes the browser on the client while the processing is taking place on the server how do I interrupt all the threads on the server so that they stop processing and releases system resources ?

Thanks in advance
ujj