How to track sessions in web application?

I am new to web design. So, can anybody tell me how to get information about all opened sessions? ( I am writing a game and i need to know abou开发者_开发技巧t all clients which are on-line at the moment ) I am using spring Mvc 3.0

Thanks for answers.

---

Sorry once more) i am dealing with my session like this:

request.getSession(true).setAttribute("client",client);
        request.getSession(true).setAttribute(Constants.SESS_AUTH, Boolean.TRUE);

my listener is

@Override
public void sessionCreated(HttpSessionEvent arg0) {
       totalActiveSessions++;
       System.out.println("sessionCreated - add one client into list");
       setOnline(arg0);
}

@Override
public void sessionDestroyed(HttpSessionEvent arg0) {
       totalActiveSessions--;
       System.out.println("sessionDestroyed - deduct one client from list");
       setOffline(arg0);
}

private void setOnline(HttpSessionEvent sessionEvent){

      HttpSession session = sessionEvent.getSession();

      ApplicationContext ctx =
            WebApplicationContextUtils.
                  getWebApplicationContext(session.getServletContext());

      SessionService sessionService = (SessionService) ctx.getBean("sessionService");

      sessionService.setClientOnLine((Client)sessionEvent.getSession().getAttribute("client"));
}

private void setOffline(HttpSessionEvent sessionEvent){

      HttpSession session = sessionEvent.getSession();

      ApplicationContext ctx =
            WebApplicationContextUtils.
                  getWebApplicationContext(session.getServletContext());

      SessionService sessionService = (SessionService) ctx.getBean("sessionService");

      sessionService.setClientOffLine((Client)sessionEvent.getSession().getAttribute("client"));
}

unfortunately it doesnt works like i want... could you recommend something