public static void addListener( SessionListener listener )
    {
        if ( listener == null )
        {
            throw new NullPointerException();
        }
        listeners.add( listener );
    }
Adds a {@link org.jivesoftware.openfire.http.SessionListener} to this session. The listener
will be notified of changes to the session.

@param listener the listener which is being added to the session.
xmppserver/src/main/java/org/jivesoftware/openfire/http/SessionEventDispatcher.java