Web app context variables?

Question

Hello all, I have another question. In my app I want all *.jsp pages to report how many currently active users are on my site. It could do this one of two ways (that i can think of),
1) Run a count of how many sessions are in the 'sessions' table in my mysql db
2) Read some sort of global context variable that is set everytime someone logs in
Obviously 1) will be a smidgin more accurate but more labor intensive than 2. Can anyone think of a better way to do this? Also if i were to go the global variable route would there be a better way to do it than
this.getServletContext().setAttribute("com.thesite.loggedin", 11)and then reading this int in the *.jsp(s), is something like this able to handle concurrent set & get (is it thread safe?)
Thanks for any help!

Answer 1

You can make use of attributeAdded() method of HttpSessionAttributeListener. Whenever any attribute is set in session, attributeAdded() method will be called and you can increment a counter in that method. Eg:
public class SessionAttributeListener implements HttpSessionAttributeListener
int count=0;
public void attributeAdded(HttpSessionBindingEvent e)
     System.out.println("session attribute added");
                 count++;
public int getCount()
return count;
}You can call SessionAttributeListener.getCount() method to count the number of active users.