First off, do some searches on threads and servlets. Depending upon where you get the information, threads in this context can be discouraged or not (see Constant Servlet Running
for a good discussion on the subject). A brief
overview of the servlet spec doesn't seem to mention anything beyond making sure things are thread safe. That out of the way I'd suggest looking into creating a single thread pool which manages the requests as a queue, so you don't have the overhead of creating so many different threads, have a single manager that manages one or more threads in a queue. Store this as a Session variable, so you can retrieve it from HTTPServletRequest, and pass a reference of the Session to the manager, which will allow you to store the count as a session variable (always access the the Session from your threads in a synchronized
way). Finally, create a test structure and hammer at it to be sure doing all of the above results in correct behavior.