在JMS队列上发布消息？

Question

i am new to JMS and going thru the example of Active MQ Hello world . Say i have a scenario whenever i make entry under employee table in DB, i have to put the message in queue.here is the producer code snippet from hello world example

public static class HelloWorldProducer  {
        public void createMessageOnQueue() {
            try {
                // Create a ConnectionFactory
                ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("vm://localhost");

                // Create a Connection
                Connection connection = connectionFactory.createConnection();
                connection.start();

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

                // Create the destination (Topic or Queue)
                Destination destination = session.createQueue("TEST.FOO");

                // Create a MessageProducer from the Session to the Topic or Queue
                MessageProducer producer = session.createProducer(destination);
                producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);

                // Create a messages
                String text = "Hello world! From: " + Thread.currentThread().getName() + " : " + this.hashCode();
                TextMessage message = session.createTextMessage(text);

                // Tell the producer to send the message
                System.out.println("Sent message: "+ message.hashCode() + " : " + Thread.currentThread().getName());
                producer.send(message);

                // Clean up
                session.close();
                connection.close();
            }
            catch (Exception e) {
                System.out.println("Caught: " + e);
                e.printStackTrace();
            }
        }
    }

Now my question is if i close the connection and session, will it close the queue also? If yes,what will happen if message has not been consumed yet?

Second question is if i need to publish the message on same queue(ie "TEST.FOO") second time , do i need to call createMessageOnQueue method second time. If yes, will it not create new queue with session.createQueue("TEST.FOO")?

Answer 1

The queue is created once and only you can delete it manually. Once the message is sent to a queue, it will wait on the queue until it's consumed (unlike topics).

You don't need to re-create the message if you want to send it twice. But then again, why would you send it two times?

I feel that your problem might be solved using JMS transactions.

Answer 2

Now my question is if i close the connection and session, will it close the queue also? If yes,what will happen if message has not been consumed yet?

message will still be on queue. No such thing as 'closing a queue'.

Second question is if i need to publish the message on same queue(ie "TEST.FOO") second time , do i need to call createMessageOnQueue method second time. If yes, will it not create new queue with session.createQueue("TEST.FOO")?

session.createQueue("TEST.FOO") does not necessarily create queue, it just get a reference to existing queue.

javadoc of session#createQueue()

Note that this method simply creates an object that encapsulates the name of a topic. It does not create the physical topic in the JMS provider. JMS does not provide a method to create the physical topic, since this would be specific to a given JMS provider. Creating a physical topic is provider-specific and is typically an administrative task performed by an administrator, though some providers may create them automatically when needed.