You need to collect all logged in users in a Set<User> in the application scope. Just hook on login and logout and add and remove the User accordingly. Basically:
public void login(User user) {
// Do your business thing and then
logins.add(user);
}
public void logout(User user) {
// Do your business thing and then
logins.remove(user);
}
If you're storing the logged-in users in the session, then you'd like to add another hook on session destroy to issue a logout on any logged-in user. I am not sure about how Grails fits in the picture, but talking in Java Servlet API, you'd like to use HttpSessionListener#sessionDestroyed() for this.
public void sessionDestroyed(HttpSessionEvent event) {
User user = (User) event.getSession().getAttribute("user");
if (user != null) {
Set<User> logins = (Set<User>) event.getSession().getServletContext().getAttribute("logins");
logins.remove(user);
}
}
You can also just let the User model implement HttpSessionBindingListener. The implemented methods will be invoked automagically whenever the User instance is been put in session or removed from it (which would also happen on session destroy).
public class User implements HttpSessionBindingListener {
@Override
public void valueBound(HttpSessionBindingEvent event) {
Set<User> logins = (Set<User>) event.getSession().getServletContext().getAttribute("logins");
logins.add(this);
}
@Override
public void valueUnbound(HttpSessionBindingEvent event) {
Set<User> logins = (Set<User>) event.getSession().getServletContext().getAttribute("logins");
logins.remove(this);
}
// @Override equals() and hashCode() as well!
}
or see here : http://www.freeimagehosting.net/image.php?2de8468a86.png