code: private MessageConsumer getConsumer(final String destinationName) {
          if (!consumers.containsKey(destinationName)) {
              Session session = getSession();
  
              Destination destination = getDestination(destinationName);
              try {
                  MessageConsumer consumer = session.createConsumer(destination);
                  consumers.put(destinationName, consumer);
              } catch (JMSException e) {
                  throw new JmsException("Unable to create consumer for destination "
                          + destinationName, e);
              }
          }
          return consumers.get(destinationName);
      }
docs: Get the `MessageConsumer`.
  
  @param destinationName destinationName
  @return JMS `MessageConsumer`.