code: private static NotificationsHandler getHandler(final String queueName,
                                                   final Properties pr) throws NotificationException {
      if (handler != null) {
        return handler;
      }
  
      synchronized (synchit) {
        handler = new JmsNotificationsHandlerImpl(queueName, pr);
      }
  
      return handler;
    }
docs: Return a handler for the system event
  
  @param queueName our queue
  @param pr jms properties
  @return NotificationsHandler
  @throws NotificationException