Question

I am new to Java EE. I have a site which requires a user to log in, and after the user logs in I would like the user to see his/her own item (e.g: shopping cart).

So that means I have to use a session to accomplish that. But how do I deal with multiple sessions?

For example multiple users login to the system as well as to the same servlet? However, can I keep multiple sessions in one servlet? Do I keep a record of each of them? How does it work?

Can someone give an example please ?

Answer 1

In servlet you have access to HttpServletRequest which provides you with a getSession() method. This methods returns session object (essentialy a key-value map), different for each user.

If you put something into that map (like shopping cart), you can retrieve it later – but only when the same user accesses the application again (not necessarily the same servlet).

public void doGet(HttpServletRequest request, HttpServletResponse response)
      throws IOException, ServletException {

    HttpSession session = request.getSession();
    session.getAttribute("cart");
    //...
    session.setAttribute("cart", whateverYouWant);

Sessions are maintained in the servlet container and looked up by session id (typically a cookie). You don’t have to implement anything yourself.