As many applications require requests coming from the same client to be associated, web applications have the responsibility to maintain this state in a special object called a session. Fortunately, Java servlets fully support sessions.
Within a servlet, a session of class HttpSession is obtained by calling the getSession() method of the HTTP request. A session object can then be manipulated with getAttribute()/setAttribute()/removeAttribute().
Implementing a shopping cart
Enhance the web application developed previously so that users can add specific songs to a shopping cart. Multiple users browsing from different computers should be able to have their distinct shopping carts. Each user should be able to clear his own cart at any time.