// user func
  @RequestMapping(
      value = {"/workspace/general/to-participate-in-the-event"},
      method = RequestMethod.GET)
  public String toParticipateInTheEvent(
      ModelMap modelMap, @RequestParam String eventId, Principal principal) {
    EventEntity eventEntity = eventService.findById(eventId);
    UserEntity userEntity = userService.findByUsername(principal.getName());
    Set<EventEntity> userEvents = userEntity.getUserEvents();
    if (eventEntity.getTheCurrentNumberOfParticipants() + 1 > eventEntity.getCountParticipants()) {
      modelMap.addAttribute("textPage", ActionMessage.THE_EXCESS_NUMBER_OF_PARTICIPANTS);
      return "pages/general/success-template-page";
    } else {
      if (null != userEvents) {
        userEvents.add(eventEntity);
      } else {
        userEvents = new HashSet<EventEntity>();
        userEvents.add(eventEntity);
      }
      userEntity.setUserEvents(userEvents);
      userService.update(userEntity);

      try {
        mailService.sendEmail(
            MailMessageText.helloLetterRegisterOfEventHeader(eventEntity),
            MailMessageText.helloLetterRegisterOfEventBody(eventEntity),
            new String[] {userEntity.getEmail()});
      } catch (MessagingException e) {
        modelMap.addAttribute("textPage", ActionMessage.ERROR_ACTION);
      }

      modelMap.addAttribute("textPage", ActionMessage.SUCCESS_EVENT_USER_REGISTRATION);
      return "pages/general/success-template-page";
    }
  }
 @RequestMapping(
     value = {"/workspace/general/refuse-to-participate-in-the-event"},
     method = RequestMethod.GET)
 public String refuseToParticipateInTheEvent(
     ModelMap modelMap, @RequestParam String eventId, Principal principal) {
   EventEntity eventEntity = eventService.findById(eventId);
   UserEntity userEntity = userService.findByUsername(principal.getName());
   Set<EventEntity> userEvents = userEntity.getUserEvents();
   userEvents.remove(eventEntity);
   userEntity.setUserEvents(userEvents);
   userService.update(userEntity);
   try {
     mailService.sendEmail(
         MailMessageText.cancelLetterRegisterOfEventHeader(eventEntity),
         MailMessageText.cancelLetterRegisterOfEventBody(eventEntity),
         new String[] {userEntity.getEmail()});
   } catch (MessagingException e) {
     modelMap.addAttribute("textPage", ActionMessage.ERROR_ACTION);
   }
   modelMap.addAttribute("textPage", ActionMessage.CANCEL_EVENT_USER_REGISTRATION);
   return "pages/general/success-template-page";
 }