Question

The code below does NOT work:

Cause:

I assume I tracked down the cause to:
http://community.jboss.org/thread/150988
=> This article says that HornetQ uses Weak References.

My Question:
Why does the code not run? (I have this code running with a slight different implementation, but the code blow fails repeatedly). My only guess is, that the
following references:

private Connection connection = null;
private Session session = null;
private MessageProducer producer = null;

are not regarded as strong references? (And this leads to the fact that the garbage collector removes the objects… But way arent they strong references?

Or is there another problem with the code (as said the code runs fine if I copy everything into one single method. But if I use the Singleton approach below the code does not work…) Another assumption was that it might have to do with ThreadLocal stuff, but I am using only a single thread…

The Code not working (stripped down):

public class JMSMessageSenderTest {
    private static final Logger logger = Logger.getLogger(JMSMessageSenderTest.class);

    private static JMSMessageSenderTest instance;

    private Connection connection = null;
    private Session session = null;
    private MessageProducer producer = null;

    private JMSMessageSenderTest() {
        super();
    }


    public static JMSMessageSenderTest getInstance() throws JMSException {
        if (instance==null) {
            synchronized(JMSMessageSenderTest.class) {
                if (instance==null) {
                    JMSMessageSenderTest instanceTmp = new JMSMessageSenderTest();
                    instanceTmp.initializeJMSConnectionFactory();
                    instance = instanceTmp;
                }
    } }
        return instance;
    }


    private void createConnectionSessionQueueProducer() throws Exception {

        try {


            Queue queue = HornetQJMSClient.createQueue("testQueue");

            connection = initializeJMSConnectionFactory();

             session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);

             producer = session.createProducer(queue);

             connection.start();

        } catch (Exception e) { 
            cleanupAfterError();
            throw e;
        }

    }


    private void cleanupAfterError() {

        if (connection != null){
             try{
                 connection.close();
             }catch(JMSException jmse) {
                 logger.error("Closing JMS Connection Failed",jmse);
             }
         }
    session = null;
    producer = null;

    }


    public synchronized void sendRequest(String url) throws Exception {

            if (connection==null) {
                createConnectionSessionQueueProducer();
            }

        try {

             //HERE THE EXCEPTION IS THROWN, at least when debugging
             TextMessage textMessage = session.createTextMessage(url);

             producer.send(textMessage); 

            } catch (Exception e) {
            cleanupAfterError();
            throw e;
        }

    }

        private Connection initializeJMSConnectionFactory() throws JMSException{

        Configuration configuration = ConfigurationFactory.getConfiguration(null, null);

        Map<String, Object> connectionParams = new HashMap<String, Object>();

        connectionParams.put(org.hornetq.core.remoting.impl.netty.TransportConstants.PORT_PROP_NAME, 5445);
        connectionParams.put(org.hornetq.core.remoting.impl.netty.TransportConstants.HOST_PROP_NAME, "localhost");

        TransportConfiguration transportConfiguration = new TransportConfiguration(NettyConnectorFactory.class.getName(), connectionParams);

        ConnectionFactory connectionFactory = (ConnectionFactory) HornetQJMSClient.createConnectionFactoryWithoutHA(JMSFactoryType.CF, transportConfiguration);

    //      return  connectionFactory.createConnection(login, password);    
        return connectionFactory.createConnection();

    }


    /**
     * Orderly shutdown of all resources.
     */
    public void shutdown() {
        cleanupAfterError();
    }


}

TestCode to run the code above

JMSMessageSenderTest jmsMessageSender = JMSMessageSenderTest.getInstance();
jmsMessageSender.sendRequest("www.example.com)");
jmsMessageSender.shutdown();

Gives the following error:

I'm closing a JMS connection you left open. Please make sure you close all JMS connections explicitly before letting them go out of scope!
The JMS connection you didn't close was created here:
java.lang.Exception
    at org.hornetq.jms.client.HornetQConnection.<init>(HornetQConnection.java:152)
    at org.hornetq.jms.client.HornetQConnectionFactory.createConnectionInternal(HornetQConnectionFactory.java:662)
    at org.hornetq.jms.client.HornetQConnectionFactory.createConnection(HornetQConnectionFactory.java:121)

Solution:

1.) You also have to Keep a reference to the ConnectionFactory (see the answer from Clebert below)

private ConnectionFactory factory = null;

2.) AND this code contains a severe hidden bug (that is not so easy to spot):
I initialized the Connection in the Constructor as well as in the createConnectionSessionQueueProducer() method. It will therefore override the old value and (as it is a Ressource that needs to be closed) will lead to a stale connection that HornetQ then will close and will then throw the error.

Thanks very very much! Markus

Answer 1

HornetQ will close the connection factory when the connection factory is released.

You need to hold a reference for the connection factory.