9.2. The Session Tracking API
Using sessions in servlets is straightforward and involves looking up the session object associated with the current request, creating a new session object when necessary, looking up information associated with a session, storing information in a session, and discarding completed or abandoned sessions. Finally, if you return any URLs to the clients that reference your site and URL-rewriting is being used, you need to attach the session information to the URLs.
Looking Up the HttpSession Object Associated with the Current Request
You look up the HttpSession object by calling the getSession method of HttpServletRequest. Behind the scenes, the system extracts a user ID from a cookie or attached URL data, then uses that ...