Re: get list of open session

Question

Hello, if i get sessions like
public ActionForward execute(ActionMapping mapping, ActionForm form,
        HttpServletRequest request, HttpServletResponse response)
            throws ServletException {
            request.getSession().removeAttribute("web_user");
  }is there is a way to find, list of open sessions, or list of ppl who loged into the system?

Answer 1

A session is associated to a user. Removing an attribute from a session will have no impact on other sessions. You will have to store the currently active users in a higher scope (one thats common to all users - ServletContext is a good choice).
You will also have to use a combination of listeners to achieve this.
Assume you have a user object bound to each session (that stores the logged in user info).
some login process inside, say a Servlet
User userObj = new User();
//userObj.setXXX() setter methods that store user data in this object
request.getSession.setAttribute("web_user", userObj);Step 1.
Create a list to hold all active users in your context object. This list is instantiated when the context fires.
public class CtxListener implements ServletContextListener{
     public void contextInitialized(ServletContextEvent ctxEvent){
          ctxEvent.getServletContext().setAttribute("currentUsers", new ArrayList());
     public void contextDestroyed(ServletContextEvent sce){}     
}Step 2
Use a HttpSessionBindingListener that informs you when a UserObject is bound to a session.
public class User implements HttpSessionBindingListener {
     //variables and get/set methods go here
     public void valueBound(HttpSessionBindingEvent event){
          //get a handle to the context page
          ServletContext ctx = event.getSession().getServletContext();
          //get a handle to the user's list ctxt attribute
          List userList = (List)ctx.getAttribute("currentUsers");
          //add this object to the user list
          userList.add(this);
     public void valueUnbound(HttpSessionBindingEvent event){
             //do nothing
            //we will remove logged out users in a different manner
}Step 3
Now at any point where you have access to the ServletContext(which is virtually everywhere in a web application), you can get the list of users in the following fashion.
//some servlet
     List currentUsers = (List)getServletContext.getAttribute("currentUsers")
}Step 4
We have to remove logged out users. Do it using a SessionListener
public class SessionListener implements HttpSessionListener{
     public void sessionCreated(HttpSessionEvent se){
     public void sessionDestroyed(HttpSessionEvent se){
          HttpSession session = event.getSession();
          ServletContext ctx = session.getServletContext();
          List currentUsers = (List)ctx.getAttribute("currentUsers");
          currentUsers.remove(session.getAttribute("web_user"));
}You should ofcourse register your listeners in web.xml
Cheers,
Ram.