如何让我的 JMS 消息侦听器无限期地收听

Question

My code has two different JMS queues on different places. It takes a message from one queue, does some processing, builds a new message, and puts it on another queue to be picked up by a different process. Although it works what I want is for the listener to listen continuously so that whenever a new message is put on the first queue it is picked up. Main method of my listener:

public static void main(String[] args) throws JMSException {
    parseArgs(args);
    AMessageListener aMessageListener = new AMessageListener();
    try {
        aMessageListener.startListener();
        Thread.sleep(100000);
        aMessageListener.destroy();
    } catch (JMSException e) {
        // TODO handle exception
        e.printStackTrace();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    aMessageListener.destroy();
}

And the code I use to start the listener:

public void startListener() throws JMSException{
    ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(ACTIVE_MQ_FACTORY_URL);
    conn = connectionFactory.createConnection(jmsBrokerUser, jmsBrokerPass);
    conn.start();

    Session session = conn.createSession(false, Session.AUTO_ACKNOWLEDGE);
    Queue queue = session.createQueue("some.in.queue");
    MessageConsumer consumer = session.createConsumer(queue);
    consumer.setMessageListener(this);
}

I have been looking online to try to find any best practices but there's little to find. An obvious way to get what I want is to put while(true) where I have the Thread.sleep(100000) . I don't really feel like that's a clean way of doing it.

Are there any different/better ways?

Answer 1

Since this is apparently a simple command-line application you could use System.in.read() so that the program exits when the user presses the enter key. Or if you wanted to prevent accidental closures you could make it so the user had to type a specific keyword like "exit" or "quit," etc.

Aside from that I don't see any problem with using while(true) although I'd use it in conjunction with Thread.sleep() , eg:

while(true) {
   Thread.sleep(100000);
}

Also, I would recommend you put aMessageListener.destroy(); in a finally block instead of having it your code twice.

Answer 2

Here's the most terse way to lock up forever

Thread.currentThread().join(); // Sleep forever, waiting for ourselves to finish

That said you should really have an application that either restarts failed connections or dies along with the connection so something higher up can restart your JVM. To that end, I would turn main into a polling loop that checks Session or Connection every second.