@Override
        public void handleEvent(Object event) throws GuacamoleException {
            if (event instanceof TunnelCloseEvent) {
                if (!delegate.tunnelClosed((TunnelCloseEvent) event)) {
                    throw new GuacamoleException("listener vetoed tunnel close request");
                }
            }
        }
Handles a TunnelCloseEvent by passing the event to the delegate listener.
If the delegate returns false, the adapter throws a GuacamoleException
to veto the tunnel connect event. All other event types are ignored.

@param event
    An object that describes the event that occurred.

@throws GuacamoleException
     If thrown by the delegate listener.
guacamole/src/main/java/org/apache/guacamole/extension/ListenerFactory.java