Online ? - Users request Vs DB Table ?

Question

Hey guys,
I'm trying to do a lilttle script that allow me to see "who's online" on my web application. I would like to see who have been logged in for the last 2 hours, let's say.
So my problem is about getting this last login/visit date. I thought there had to be something to do with request (HttpServletRequest interface) and/or Hibernate sessions, but after searching for 3 hours I've only found how to get back the data for the current user, and anyway, it doesn't work really well at all....saying me my last visit/session creation was like 1 second ago....
So, I would like to know if you have any idea how I could implement this script.
I thought about creating a table in my DB containing the last action timestamp with the id of the member, but it doesn't sound to me as the "cleanest" solution, there is surely a way to check that using the sessions and request. It would mean to had a sql request to every page... If request/sessions already do something that look like that, it's dumb to repeat it....
I've also looked at Jboss cache but didn't find any interesting thing.
Have you guys any idea about how I could fix my problem ? Any ideas ?
I'm using hibernate and jboss (and struts but we don't really care here...).
I will look to every interesting/intelligent suggestion =P
Thanx =}

Answer 1

DB table would be the way to go. Write a class that implements an HttpSessionListener and update that table on sessionCreated and sessionDestroyed events. So, every time a new HttpSession gets created (user login) insert a new row with the login timestamp of the user. When session expires (by either explicitely calling invalidate on a session or when it expires on its own, update table with a logout timestamp.) Once you have that data in place you can then run some reports to see who, when and for how long were logged in and were using your application. This will have some time lag, especially if the user decides not to logout but simply close the browser so your logout timestamp will be off by the amount of time set for session expiration. But, for the most part you can control it using JavaScript events, say call some piece of JavaScript on unload of the browser window, which in turn will call your Java code to invalidate user's session. Otherwise, you can simply rely on your session expiration time. You can set it to expire as soon as possible (to avoid long time lags but keep it alive for as long as requred by your specs). I hope this helps ...