Problem with beans in session scope

Question

Hello,
I developped a website using JSP/Tomcat and I can't figure out how to fix this problem.
I am using beans in session scope to know when a user is actualy logged in or not and to make some basic informations about him avaible to the pages. I then add those beans to an application scope bean that manages the users, letting me know how many are logged in, etc... I store the user beans in a Vector list.
The problem is that the session beans never seem to be destroyed. I made a logout page which use <jsp:remove/> but all it does is to remove the bean from the scope and not actualy destroying it. I have to notify the application bean that the session is terminated so I manualy remove it from its vector list.
But when a user just leave the site without using the logout option, it becomes a problem. Is there a way to actualy tell when a session bean is being destroyed ? I tried to check with my application bean if there are null beans in the list but it never happens, the user bean always stays in memory.
Is there actualy a way for me to notify the application bean when the user quits the website without using the logout link ? Or is the whole design flawed ?
Thanks in advance.
Nicolas Jaccard

Answer 1

I understand I could create a listener even with my current setup Correct, you configure listeners in web.xml and they are applicable to a whole web application irrespective of whether you use jsp or servlets or both. SessionListeners would fire when a session was created or when a session is about to be dropped.
but I do not know how I could get a reference of the application bean in >question. Any hint ?From your earlier post, I understand that you add a UserBean to a session and then the UserBean to a vector stoed in application scope.
Something like below,
UserBean user = new UserBean();
//set  bean in session scope.
session.setAttribute("user", user);
//add bean to a Vector stored in application scope.
Vector v = (Vector)(getServletContext().getAttribute("userList"));
v.add(user);If you have done it in the above fashion, you realize, dont you, that its the same object that's added to both the session and to the vector stored in application scope.
So in your sessionDestroyed() method of your HttpSessionListener implementation,
void sessionDestroyed(HttpSessionEvent event){
     //get a handle to the session
     HttpSession session = event.getSession();
      //get a handle to the user object
      UserBean user = (UserBean)session.getAttribute("user");
       //get a handle to the application object
      ServletContext ctx = session.getServletContext();
       //get a handle to the Vector storing the user objs in application scope
        Vector v = (Vector)ctx.getAttribute("userList");
       //now remove the object from the Vector passing in the reference to the object retrieved from the Session.
        v.removeElement(user);
}That's it.
Another approach would be to remove the User based on a unique identifier. Let's assume each User has a unique id (If your User has no such feature, you could still add one and set the user id to the session id that the user is associated with)
void sessionDestroyed(HttpSessionEvent event){
     //get a handle to the session
     HttpSession session = event.getSession();
      //get a handle to the user object
      UserBean user = (UserBean)session.getAttribute("user");
       //get the unique id of the user object
       String id = user.getId();
       //get a handle to the application object
      ServletContext ctx = session.getServletContext();
       //get a handle to the Vector storing the user objs in application scope
        Vector v = (Vector)ctx.getAttribute("userList");
       //now iterate all user objects in the Vector
       for(Iterator itr = v.iterator(); itr.hasNext()) {
               User user = (User)itr.next();               
                if(user.getId().equals(id)) {
                       //if user's id is same as id of user retrieved from session
                       //remove the object
                       itr.remove();
}Hope that helps,
ram.