The Session JSP tag library provides tags for reading or modifying client HttpSession information.
A servlet container uses an HttpSession to store information about a clients session on the server. By default a JSP page will create a session for a user. Code: JSP 1.2
Redirects to the given URL in case of the session does not keep the object with the given name. You may save some object in the session as an indicator of user's authorization. As soon as his session is over, it redirects him to the start page. Code: JSP 1.2