Question

I have a single threaded ActiveMQ consumer written in Java. All I’m trying to do is receive() a messsage from the queue, attempt to send it to a web service, and if it succeeds acknowledge() it. If the web service call fails, I want the message to stay on the queue and be resent after some timeout.

It’s more or less working, except for the resending part: each time I restart my consumer, it gets one message for each that’s still on the queue, but after failing to send them, the messages are never resent.

My code looks like:

public boolean init() throws JMSException, FileNotFoundException, IOException {
    ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(user, password, url);
    RedeliveryPolicy policy = new RedeliveryPolicy();
    policy.setInitialRedeliveryDelay(500);
    policy.setBackOffMultiplier(2);
    policy.setUseExponentialBackOff(true);

    connectionFactory.setRedeliveryPolicy(policy);
    connectionFactory.setUseRetroactiveConsumer(true); // ????
    Connection connection = connectionFactory.createConnection();

    connection.setExceptionListener(this);
    connection.start();

    session = connection.createSession(transacted, ActiveMQSession.INDIVIDUAL_ACKNOWLEDGE);
    destination = session.createQueue(subject); //???

    consumer = session.createConsumer(destination);
    //consumer.setMessageListener(this); // message listener had same behaviour

}

private void process() {
    while(true) {
        System.out.println("Waiting...");
        try {
            Message message = consumer.receive();
            onMessage(message);
        } catch (JMSException e) {
            e.printStackTrace();
        }
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

@Override
public void onMessage(Message message) {
    System.out.println("onMessage");
    messagesReceived++;

    if (message instanceof TextMessage) {
        try {
            TextMessage txtMsg = (TextMessage) message;
            String msg = txtMsg.getText();

            if(!client.sendMessage(msg)) {
                System.out.println("Webservice call failed. Keeping message");
                //message.
            } else {
                message.acknowledge();
            }

            if (transacted) {
                if ((messagesReceived % batch) == 0) {
                    System.out.println("Commiting transaction for last " + batch + " messages; messages so far = " + messagesReceived);
                    session.commit();
                }
            }
        } catch (JMSException e) {
            e.printStackTrace();
        }
    }
}

I’m not currently using transactions (maybe I should be?).

I’m sure I’m missing something easy and will be slapping my forehead soon but I can’t seem to figure out how this is supposed to work. Thanks!

---

EDIT: Can’t answer this myself as not enough rep:

OK, after some more experimentation, it turns out transactions are the only way to do this. Here is the new code:

public boolean init() throws JMSException, FileNotFoundException, IOException {
    ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(user, password, url);
    RedeliveryPolicy policy = new RedeliveryPolicy();
    policy.setInitialRedeliveryDelay(1000L);
    policy.setMaximumRedeliveries(RedeliveryPolicy.NO_MAXIMUM_REDELIVERIES);

    connectionFactory.setRedeliveryPolicy(policy);
    connectionFactory.setUseRetroactiveConsumer(true);
    Connection connection = connectionFactory.createConnection();

    connection.setExceptionListener(this);
    connection.start();

    session = connection.createSession(transacted, ActiveMQSession.CLIENT_ACKNOWLEDGE);
    destination = session.createQueue(subject);

    consumer = session.createConsumer(destination);
}

@Override
public void onMessage(Message message) {
    System.out.println("onMessage");
    messagesReceived++;

    if (message instanceof TextMessage) {
        try {
            TextMessage txtMsg = (TextMessage) message;
            String msg = txtMsg.getText();

            if(client.sendMessage(msg)) {
                if(transacted) {
                    System.out.println("Call succeeded - committing message");
                    session.commit();
                }
                //message.acknowledge();
            } else {
                if(transacted) {
                    System.out.println("Webservice call failed. Rolling back message");
                    session.rollback();
                }
            }

        } catch (JMSException e) {
            e.printStackTrace();
        }
    }
}

Now, the message is being resent every 1000ms as specified in the Redelivery Policy.

Hope this helps someone else! 🙂

Answer 1

You don’t have to use transactions, CLIENT_ACK/Session.recover() will work as well…

Messages are redelivered to a client when any of the following occurs:

• A transacted session is used and rollback() is called.
• A transacted session is closed before commit is called.
• A session is using CLIENT_ACKNOWLEDGE and Session.recover() is called.

see http://activemq.apache.org/message-redelivery-and-dlq-handling.html