how to get online users

dear vaadin users, how to get users state (online, offline, idle) like chat application

One basic way I can think of, is implement a singleton user information bean (using a concurrent list / map!?). After a successful login you’d add the user to the list, on session end, browser close, etc you’d remove him from the list. Whenever you need to see if someone’s online, you just query the info bean.