19/02/25
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                                        Session Tracking
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Q)What is the purpose of session tracking?
=>To make end-user's interaction with the website stateful,we need to implement
session tracking.

Q)What is a session?

=>In general, time period between user's login and logout is nothing but a session.

=>In a Java web application, a session is nothing but HttpSession object.

Q)What is session tracking?
=>Keeping track of user's interaction with the website in a series of client-server interactions is nothing but session tracking.

  =>Two things are involved in session tracking.
             1)user/client identification
	     2)user's data management.
Q)How to implement session tracking  in a Java web application?
    Step 1:- create the session.
               HttpSession session=request.getSession();

    Step 2:- Deal with user's data in session scope                


    Step 3:- End the session

Q)What happens in the background when the following statement is executed?
        HttpSession session=request.getSession();

=>When getSession() method is called on HttpServletRequest object, the following things happen in order.

1) request object is evaluated for in coming session id.

    Case i:- session id not found in the request object.

2)Container creates a brand new HttpSession object. It also generates a unique
session id corresponding to that session object. This session id & session object
are maintained by the container as key value pairs.

3)Session Id is written into response object.

4)HttpSession object reference is returned to the servlet.

    Case ii:- session  id is found in the request object.

      2)Container picks up the incoming session id from the request object
         and searches for the corresponding HttpSession object.

      3)Container doesn't create a new HttpSession object. It returns the the reference
      of already existing HttpSession object.

      4)Session id is written into the response object