code: @Controller(events = {EventType.DIRECT_MENTION, EventType.DIRECT_MESSAGE})
      public void onReceiveDM(WebSocketSession session, Event event) {
          reply(session, event, "Hi, I am " + slackService.getCurrentUser().getName());
      }
docs: Invoked when the bot receives a direct mention (@botname: message)
  or a direct message. NOTE: These two event types are added by jbot
  to make your task easier, Slack doesn't have any direct way to
  determine these type of events.
  
  @param session
  @param event