"Alternative Approaches to Architecting Logon and User Management"
Vol. 8, Issue 3, p. 23

	



Listing 1

      String username = request.getParameter("username");

      HttpSession session = ((HttpServletRequest)request).getSession(true);

      boolean liu = LoggedInUserTable.isLoggedInUser(username);
  
      if (!liu)
      {
       LoggedInUserTable.addLoggedInUser(session.getId(), username);
      }
      else
      {
       String userSessionId = LoggedInUserTable.getSessionId(username);
        if ( userSessionId != session.getId())
        {
         ((HttpServletResponse)response).sendRedirect("/Messages/notice.jsp");
        }
      
      }

Listing 2

     public class UserTracker implements  HttpSessionListener {
  
     String sessionId = null;

     public void sessionCreated(HttpSessionEvent e) {
   
      }
      
      public void sessionDestroyed(HttpSessionEvent e) {
      LoggedInTable.removeLoggedInUser(e.getSession().getId());

      }

     }

Listing 3

     public class LoggedInUserTable {

     /** A Hashtable of all of the active users. */

     private static Hashtable LoggedInUsers = new Hashtable ();

     public static boolean isLoggedInUser (String username) {
     return  LoggedInUsers.containsValue(username);
     }

     public static void addLoggedInUser ( String sessionId, String username) {
     LoggedInUsers.put (sessionId, username);
     }

     public static String getSessionId(String username) {
     return (String) LoggedInUsers.get(username);
     }