code: private Destination getDestination(final String destinationName) {
          if (!destinations.containsKey(destinationName)) {
              Destination destination = destinationSupplier.apply(destinationName);
              destinations.put(destinationName, destination);
          }
          return destinations.get(destinationName);
      }
docs: Get the destination.
  
  @param destinationName destinationName
  @return JMS destination which is a queue or topic.