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?
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.
Thanks for the information,
how does it get to work,
well i have three classes, one for
HttpSessionListener - SessionListener()
ServletContextListener - CtxListener()
HttpSessionBindingListener - UserListener()
for the 3 steps, and put them into a web.xml as well,
<!-- Listeners -->
<listener>
<listener-class>com.web.util.session.SessionListener</listener-class>
</listener>
<listener>
<listener-class>com.web.util.session.CtxListener</listener-class>
</listener>
<listener>
<listener-class>com.web.util.session.UserListener</listener-class>
</listener>
how how does it add the users?
and i have
loginInAction {
..
// user is the , user object
request.getSession().setAttribute("web_user", user);
}
i did that, but its not adding, i get list of empty array of usrs. when i do the listing, on jsp as;
List currentUser = (List)getServletContext().getAttribute("currentUsers");
<%= currentUser.size() %>
Hello,
I change a code around;
this is what i got
public class UserTracker implements HttpSessionBindingListener {
private static UserTracker instance = null;
static List _activeUsers = new ArrayList();
public UserTracker() {
super();
}
public static List getUserTracker() { return _activeUsers; }
public static void setUserTracker(List activeUsers) { _activeUsers = activeUsers; }
public static UserTracker getInstance() {
if (instance == null) {
instance = new UserTracker();
}
return instance;
}
public void valueBound(HttpSessionBindingEvent event) {
_activeUsers.add(event.getSession().getAttribute("_user"));
}
public void valueUnbound(HttpSessionBindingEvent event) {
//_activeUsers.remove(event.getSession().getAttribute("_user"));
}
}
and
public class UserTrackerRemove implements HttpSessionListener{
private static Logger logger = Logger.getLogger(UserTrackerRemove.class);
public void sessionCreated(HttpSessionEvent se){
}
public void sessionDestroyed(HttpSessionEvent se){
HttpSession session = se.getSession();
ServletContext ctx = session.getServletContext();
List currentUsers = UserTracker.getUserTracker();
currentUsers.remove(session.getAttribute("_user"));
UserTracker.setUserTracker(currentUsers);
}
}
and put
login {
..
request.getSession().setAttribute("_user", user);
request.getSession().setAttribute("tracker", UserTracker.getInstance());
..
}
and put them both on xml as
<!-- Listeners -->
<listener>
<listener-class>com.web.util.UserTracker</listener-class>
</listener>
<listener>
<listener-class>com.web.util.UserTrackerRemove</listener-class>
</listener>
and now its works; i get the list as
List currentUser = UserTracker.getUserTracker();
but when user loged out or timed out, user do not remove from the list, why is that, where did i went wrong? :)
Hello, can some one able to help me,
i just cant get to work the HttpSessionListener,
i put few debug statements within the
public class UserTrackerRemove implements HttpSessionListener{
private static Logger logger = Logger.getLogger(UserTrackerRemove.class);
public void sessionCreated(HttpSessionEvent se){
}
public void sessionDestroyed(HttpSessionEvent se){
HttpSession session = se.getSession();
ServletContext ctx = session.getServletContext();
List currentUsers = UserTracker.getUserTracker();
currentUsers.remove(session.getAttribute("_user"));
UserTracker.setUserTracker(currentUsers);
}
}
but its not running, when i log out, do i have to call it in some other way?
Hi,
I had the same struggle. I notice that when a session is destroyed its impossible to retrieve the session attribute. The only thing which is still available is the session ID. That is why I used a Hashtable with a session ID as key. Now I can manage the userList.
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
Hashtable userList = (Hashtable)ctx.getAttribute("currentUsers");
//add this object to the user list
userList.put(event.getSession().getId(),this);
}
public void valueUnbound(HttpSessionBindingEvent event){
ServletContext ctx = event.getSession().getServletContext();
Hashtable userList = (Hashtable)ctx.getAttribute("currentUsers");
//remove this object to the user list
userList.remove(event.getSession().getId());
}
