title: How to get list of active users in tomcat
body: <p>How do I get the list of active users logged in using <code>session</code>.</p>
  
  <p>I have tried <code>session.getOpenSessions()</code> but the value is <code>null</code>.</p>
  
  <p>This one I need it for my web socket chat program...</p>
  
  <p>Pls help me. </p>