Q)How are protocols classified?
       1)stateless protocol
       2)stateful protocol
=>If server has got no memory of prior connections, the protocol is said to be
stateless. If it has, it is stateful.
=>FTP(File Transfer Protocol) is a stateful protocol.
=>HTTP is a stateless protocol.

Note:- HTTP provides better performance but poses some challenges to the 
web application developers as user interaction with the website should be stateful.

Q)What is the purpose of session tracking?
=>To make 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 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 is 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