ActiveMQ dynamic queues

[dave taubler]

Hi,

With ActiveMQ, one can create a queue (or topic) on the fly, which is pretty cool. But I'm wondering if the queue can actually be created by a Consumer rather than a Producer.

Specifically, here's the issue I'm having. On application startup, I initialize a class that implements MessageListener and registers itself like this:

...
Destination destination = session.createQueue("unique-subject");
MessageConsumer consumer = session.createConsumer(destination);
consumer.setMessageListener(this); 

later on, a producer creates a queue also called "unique-subject" and places a message on it. What happens is the first time after I restart ActiveMQ, my MessageListener's onMessage() method is never called. However, when I subsequently run the application, onMessage() is in fact called (as long as I don't restart ActiveMQ).

This makes me think that the MessageListener is not being properly bound until the queue is created by a Producer. Is that how ActiveMQ actually behaves, or is this likely my error?

Thanks in advance.

[Pradeep bhatt]

Just calling the createQueue creates a queue dynamically.

http://activemq.apache.org/how-do-i-create-new-destinations.html

If it is not working for you someone from ActiveMQ forum may be able to help you.

[Pradeep bhatt]

You can check the detsinations created either using JMX or Active MQ API
http://activemq.apache.org/how-can-i-see-what-destinations-are-used.html

[dave taubler]

Thanks, Pradip. I basically just needed confirmation that my understanding about ActiveMQ was correct. There must be user-error (i.e. me) somewhere.

[dave taubler]

In case anyone else is having a similar issue, my problem seemed to stem from my not committing the Session after creating & adding the MessageListener. Once I added

session.commit()

after

MessageConsumer consumer = session.createConsumer(destination);
consumer.setMessageListener(this);
connection.start();

, my MessageListener immediately began receiving onMessage() notifications.

[Pradeep bhatt]

Thanks dave for letting us know the problem

[Shaan Shar]

Hi I was also trying to create a topic on the fly, but somehow it's giving following error.

"JNDI API lookup failed: javax.naming.NameNotFoundException: myTopic"

Here is my code.

import java.util.Properties;

import javax.jms.Connection;
import javax.jms.ConnectionFactory;
import javax.jms.Destination;
import javax.jms.JMSException;
import javax.jms.MessageProducer;
import javax.jms.Session;
import javax.jms.TextMessage;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public final class SimpleProducer {

  private static final Log LOG = LogFactory.getLog(SimpleProducer.class);

  private SimpleProducer() {
    //TODO Do nothing
  }

  /**
   * @param args the destination name to send to and optionally, the number of messages to send
   */
  public static void main(String[] args) {
    Context jndiContext = null;
    ConnectionFactory connectionFactory = null;
    Connection connection = null;
    Session session = null;
    Destination destination = null;
    MessageProducer producer = null;
    String destinationName = null;
    final int numMsgs;

    if ((args.length < 1) || (args.length > 2)) {
      LOG.info("Usage: java SimpleProducer <destination-name> [<number-of-messages>]");
      System.exit(1);
    }
    destinationName = args[0];
    LOG.info("Destination name is " + destinationName);
    if (args.length == 2) {
      numMsgs = (new Integer(args[1])).intValue();
    } else {
      numMsgs = 1;
    }
    Properties props = new Properties();
    props.setProperty(Context.INITIAL_CONTEXT_FACTORY,"org.apache.activemq.jndi.ActiveMQInitialContextFactory");
    props.setProperty(Context.PROVIDER_URL,"tcp://hostname:61616");
    /*
     * Create a JNDI API InitialContext object
     */
    try {
      jndiContext = new InitialContext(props);
    } catch (NamingException e) {
      LOG.info("Could not create JNDI API context: " + e.toString());
      System.exit(1);
    }

    /*
     * Look up connection factory and destination.
     */
    try {
      connectionFactory = (ConnectionFactory) jndiContext.lookup("ConnectionFactory");
      destination = (Destination) jndiContext.lookup(destinationName);
    } catch (NamingException e) {
      LOG.info("JNDI API lookup failed: " + e);
      System.exit(1);
    }

    /*
     * Create connection. Create session from connection; false means session is not transacted.
     * Create sender and text message. Send messages, varying text slightly. Send end-of-messages
     * message. Finally, close connection.
     */
    try {
      connection = connectionFactory.createConnection();
      session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
      producer = session.createProducer(destination);
      TextMessage message = session.createTextMessage();
      for (int i = 0; i < numMsgs; i++) {
        message.setText("This is message " + (i + 1));
        LOG.info("Sending message: " + message.getText());
        producer.send(message);
      }

      /*
       * Send a non-text control message indicating end of messages.
       */
      producer.send(session.createMessage());
    } catch (JMSException e) {
      LOG.info("Exception occurred: " + e);
    } finally {
      if (connection != null) {
        try {
          connection.close();
        } catch (JMSException jmsException) {
          jmsException.printStackTrace();
        }
      }
    }
  }
}

Here is my jndi.properties file.

java.naming.factory.initial = org.apache.activemq.jndi.ActiveMQInitialContextFactory
java.naming.provider.url = tcp://localhost:61616
queue.MyQueue = localOD.localODQueue
topic.MyTopic = localOD.localODTopic

Can anybody explain what's wrong with this code? I am a newbie in JMS


FYI, I took this code from here