CODEWITHSUNDEEP
javajmsactivemq-classicmessage-queuespring-jms
Cameron Bauer
Cameron Bauer

Reputation: 21

JMS QueueBrowser hanging on getEnumeration()

I'm fiddling around with a JMS Queue using ActiveMQ and I wanted to work out a Queue Browser. I've looked up some examples on the web but I'm having quite a bit of trouble getting it to work.

Here is the relevant code:

   QueueBrowser browser = template.execute(new SessionCallback<QueueBrowser>() {
   public QueueBrowser doInJms(Session session) throws JMSException {
           return session.createBrowser(queue);
                    }
                }, true);

               Enumeration messages = browser.getEnumeration();
               int num = 0;
                while(messages.hasMoreElements()) {
                    messages.nextElement();
                    num +=1;
                }
                logger.info("Num = " + num);

I've injected in the template and queue, and using some log statements I have verified that they are the objects I want. I can even retrieve the queue from the QueueBrowser once it is instantiated. I've populated the queue with about 100 messages and am reading them off using a custom JmsMessageListener that has about a 1 sec delay between reads.

However, the issue is that the code hangs around the while(messages.hasMoreElements() line. From debugging, it never even goes inside the loop. If I have that line of code in a logger to check the value the hanging also occurs.

If I merely use the enumeration to nextElement() without looping, then I'm returned a null value. I cannot determine whether this means the queue or enumeration is empty. If so, shouldn't messages hasMoreElements() return a proper boolean value?

Could the issue be that I'm reading messages with a JmsMessageListener? Am I using the template wrong? I can't really determine where something is going wrong because it appears that 90% of it is working, its just the last 10% that seems to be acting oddly.

EDIT:

Managed to get it working. My session was being closed before I ever called the browser to do anything. All I needed to do was move the browser code into the doInJms block as such:

            template.execute(new SessionCallback<QueueBrowser>() {
                public QueueBrowser doInJms(Session session) throws JMSException {
                    QueueBrowser browser =  session.createBrowser(queue);
                    Enumeration messages = browser.getEnumeration();
                    int num = 0;
                    logger.info("" + messages.hasMoreElements());
                    while(messages.hasMoreElements()) {
                        messages.nextElement();
                        num +=1;
                    }
                    logger.info("Num = " + num);
                    return null;
                }
            }, true);

Upvotes: 1

Views: 3245

Answers (1)

Cameron Bauer
Cameron Bauer

Reputation: 21

The solution is in the edit above, however I wanted to post this for ease of access. I merely needed to move the browser code inside the doInJms block. An additional solution is to use template.browse and create a new BrowserCallback to override. In the end the solution is similar.

        template.execute(new SessionCallback<QueueBrowser>() {
            public QueueBrowser doInJms(Session session) throws JMSException {
                QueueBrowser browser =  session.createBrowser(queue);
                Enumeration messages = browser.getEnumeration();
                int num = 0;
                logger.info("" + messages.hasMoreElements());
                while(messages.hasMoreElements()) {
                    messages.nextElement();
                    num +=1;
                }
                logger.info("Num = " + num);
                return null;
            }
        }, true);

Upvotes: 1

Related Questions