如何判断JMS队列是启动还是停止？

Question

I have a Java service which is getting messages from an Oracle Advanced Queue. I can create the connection and listen and get messages OK. I can see that you can stop and start listening for messages, so I have implemented controls for that. However, I would like to be able to report on the current status of the listener. I can see if it's there, but how can I tell if it's stopped or started?

I have a container class along the lines of ( Listener is my own class (implementing both MessageListener and ExceptionListener ) which actually does something with the message)

public class QueueContainer {
  private static final String QUEUE_NAME = "foo";

  private final Connection dbConnection;
  private final QueueConnection queueConnection;
  private final QueueSession queueSession;
  private final Queue queue;
  private final MessageConsumer consumer;
  private final Listener listener;

public QueueContainer(final Connection dbConnection ) {
    try {
      this.dbConnection = dbConnection;
      queueConnection = AQjmsQueueConnectionFactory.createQueueConnection(dbConnection);
      queueSession = queueConnection.createQueueSession(false, Session.CLIENT_ACKNOWLEDGE);
      queue = ((AQjmsSession) queueSession).getQueue(context.getEnvironment(), QUEUE_NAME);
      consumer = queueSession.createConsumer(queue);
      listener = new Listener(QUEUE_NAME);
      consumer.setMessageListener(listener);
      queueConnection.setExceptionListener(listener);
    } catch (JMSException | SQLException e) {
      throw new RunTimeException("Queue Exception", e);
    }
  }
  public void startListening() {
    try {
      queueConnection.start();

    } catch (JMSException e) {
      throw new RunTimeException("Failed to start listening to queue", e);
    }
  }

  public void stopListening() {
    try {
      queueConnection.stop();
    } catch (JMSException e) {
      throw new RunTimeException("Failed to stop listening to queue", e);
    }
  }

  public void close() {
    if (queueConnection != null) {
      try {
        queueConnection.close();
      } catch (JMSException e) {
        throw new RunTimeException("Failed to stop listening to queue", e);
      }
    }
  }

  public boolean isRunning() {
    try {
      // This doesn't work - I can't distinguish between started and stopped
      return queueConnection.getClientID() != null;
    } catch (JMSException e) {
      LOGGER.warn("Failed to get queue client ID", e);
      return false;
    }
  }

I can't see what to put in isRunning that could distinguish between a stopped and started listener

Answer 1

There is no JMS API call to determine whether or not a javax.jms.Connection is started.

To be clear, the queue itself is not the entity that is started or stopped. The connection is started or stopped.

You may be able to get this information from the Oracle Advanced Queue implementation object, but I'm not familiar with that implementation so I can't say. Obviously any solution using an implementation object rather than the standard API will not be portable.

Answer 2

The JMS API assumes you know yourself what you did. So why not add a boolean flag and keep track of this ?

    private volatile boolean isListening = false;
    ...

    public void startListening() {
    try {
      queueConnection.start();
      isListening = true;
    } catch (JMSException e) {
      throw new RunTimeException("Failed to start listening to queue", e);
    }
  }

  public void stopListening() {
    try {
      queueConnection.stop();
      isListening = false;
    } catch (JMSException e) {
      throw new RunTimeException("Failed to stop listening to queue", e);
    }
  }

  public void close() {
    if (queueConnection != null) {
      try {
        queueConnection.close();
        isListening = false;
      } catch (JMSException e) {
        throw new RunTimeException("Failed to stop listening to queue", e);
      }
    }
  }

  public boolean isRunning() {
      return isListening;
  }