code: public void addNotification(@Observes final DesignerNotificationEvent event) {
          if (user.getIdentifier().equals(event.getUserId())) {
  
              if (event.getNotification() != null && !event.getNotification().equals("openinxmleditor")) {
                  final NotificationPopupView view = new NotificationPopupView();
                  activeNotifications.add(view);
                  view.setPopupPosition(getMargin(),
                                        activeNotifications.size() * SPACING);
  
                  view.setNotification(event.getNotification());
                  view.setType(event.getType());
                  view.setNotificationWidth(getWidth() + "px");
                  view.show(new Command() {
  
                      @Override
                      public void execute() {
                          //The notification has been shown and can now be removed
                          deactiveNotifications.add(view);
                          remove();
                      }
                  });
              }
          }
      }
docs: Display a Notification message
  @param event