Asynchronous Hello ActiveMQ consumer

It is simple to modify the hello ActiveMQ example to change the consumer from syncronous to asyncronous.

If we want to asynchronously consume a message, we have to create a class that implements the JMS MessageListener interface, something like:

private class MyMessageListener implements MessageListener {
    @Override
    public void onMessage(Message message) {
        if(message instanceof TextMessage) {
            try {
                logger.info("Received {} ", ((TextMessage) message).getText());
            } catch (JMSException e) {
                logger.error("Can't extract text from received message", e);
            }
        }
        else
            logger.info("Unexpected non-text message received.");
    }
}

Then the consumer code changes only slightly:

MessageConsumer consumer = session.createConsumer(destination);
consumer.setMessageListener(new MyMessageListener()); // 1
try{ Thread.sleep(1000); } catch(InterruptedException e) {} // 2

1. Associate to the consumer an instance of our listener.
2. Usually we should implement a more sophisticated way of keeping alive the consumer till all the relevant messages are consumed. But for this simple example sleeping for a second should be enough.

The Java source code for the hello producer-consumer example, both in the synchronous and asynchronous flavor, is on github.