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How does the MessageListener running in JMS? Can it load messages in the queue in real time?

I want to load the JMS messages in a queue in real time, if is a consumer.setMessageListener(myListener) viable and how it works?
I'm not sure how a listener working. I wrote a listener like below.
public class JmsMessageListenerExample {
public static void main(String[] args) throws URISyntaxException, Exception {
BrokerService broker = BrokerFactory.createBroker(new URI(
"broker:(tcp://localhost:61616)"));
broker.start();
Connection connection = null;
try {
// Producer
ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(
"tcp://localhost:61616");
connection = connectionFactory.createConnection();
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
Queue queue = session.createQueue("customerQueue");
String payload = "Important Task";
Message msg = session.createTextMessage(payload);
MessageProducer producer = session.createProducer(queue);
System.out.println("Sending text '" + payload + "'");
producer.send(msg);
// Consumer
MessageConsumer consumer = session.createConsumer(queue);
consumer.setMessageListener(new ConsumerMessageListener("Consumer"));
connection.start();
} finally {
if (connection != null) {
connection.close();
}
broker.stop();
}
}
After I run the JmsMessageListenerExample, it completed quickly and I didn't received any messages. If a listener should keep on running until I stop it?

When you set a JMS message listener it will receive messages asynchronously in its own thread (invoked by the JMS implementation). In your case you need to prevent main from exiting and stopping your application because when that happens the MessageListener will be terminated.
Also, when you say "load the JMS messages in a queue in real time" I assume you mean "consume JMS messages from a queue as soon as possible when queue receives them." If that's the case then a JMS message listener is the right approach.

Why does my JMS client not consume messages from the Topic?

I have ActiveMQ running on the localhost using the default port, 61616. I put some messages in a Topic called topic.STUDENTS. I have a client program that I am trying to use to read the messages in the Topic. Here is the main part of the program that does not work as expected. I was expecting to get some of the message back but instead I just receive null.
public void receiveMessages() throws URISyntaxException, JMSException, Exception {
try {
//Create a ConnectionFactory
ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory("tcp://localhost:61616");
//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.createTopic("topic.STUDENTS");
//Create a MessageConsumer from the Session to the Topic or Queue
MessageConsumer consumer = session.createConsumer(destination);
//Wait for a message
Message message = consumer.receive(1000);
if (message instanceof TextMessage) {
TextMessage textMessage = (TextMessage) message;
String text = textMessage.getText();
System.out.println("Received: " + text);
} else {
System.out.println("Received: " + message);
}
consumer.close();
session.close();
connection.close();
} catch(Exception e) {
System.out.println("Caught: " + e);
e.printStackTrace();
}
}
This code basically apes the code from ActiveMQ 'Hello World' example: http://activemq.apache.org/hello-world.html
Does anyone know why I do not receive any messages from the Topic? Here is one message that is in the Topic that I can see through the ./activemq browse topic.STUDENTS command:
JMS_BODY_FIELD:JMSText = Invention-my-dear-friends-is-93%-perspiration-6%-electricity
JMS_HEADER_FIELD:JMSExpiration = 0
JMS_HEADER_FIELD:JMSMessageID = ID:user-thinkpad-335i-59919-1457977678059-1:1:1:1:3
JMS_HEADER_FIELD:JMSPriority = 4
JMS_HEADER_FIELD:JMSDestination = topic.STUDENTS
JMS_HEADER_FIELD:JMSTimestamp = 1457977678409
JMS_HEADER_FIELD:JMSRedelivered = false
JMS_HEADER_FIELD:JMSDeliveryMode = persistent

Topics do not retain messages by default, so if you start the consumer after you've produced the messages then any message that was sent before the consumer arrived is gone. If you want to consume messages that were produced while your consumer was offline then you need to use a Queue or register a durable Topic subscriber on the Topic prior to producing the messages.

How to start ActiveMQ when tomcat starts?

How do I configure my J2EE application so that I can invoke ActiveMQ service along with tomcat server? I am aware about embedded broker, here asking how to start the ActiveMQ whenever I start tomcat
Current Code (works fine) :
Now I want to remove main() method and use the code to run when tomcat runs.
public class JMSService {
public void produceJMS() throws NamingException, JMSException {
ConnectionFactory connFactory = new ActiveMQConnectionFactory(ActiveMQConnection.DEFAULT_BROKER_URL);
Connection conn = connFactory.createConnection();
conn.start();
Session session = conn.createSession(false,Session.AUTO_ACKNOWLEDGE);
Destination destination = session.createQueue("testQueue");
MessageProducer producer = session.createProducer(destination);
producer.setDeliveryMode(DeliveryMode.PERSISTENT);
TextMessage message = session.createTextMessage("Test Message ");
// send the message
producer.send(message);
System.out.println("sent: " + message);
}}
Here is my consumer :
public class JMSReceiver implements MessageListener,ExceptionListener {
public static void main(String args[]) throws Exception {
JMSReceiver re = new JMSReceiver();
re.receiveJMS();
}
public void receiveJMS() throws NamingException, JMSException {
ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(ActiveMQConnection.DEFAULT_BROKER_URL);
Connection connection = connectionFactory.createConnection();
connection.start();
Session session = connection.createSession(false,Session.AUTO_ACKNOWLEDGE);
// Getting the queue 'testQueue'
Destination destination = session.createQueue("testQueue");
MessageConsumer consumer = session.createConsumer(destination);
// set an asynchronous message listener
JMSReceiver asyncReceiver = new JMSReceiver();
consumer.setMessageListener(asyncReceiver);
connection.setExceptionListener(asyncReceiver);
}
#Override
public void onMessage(Message message) {
System.out.println("Received message : " +message);
}
}

What #Tim Bish said is correct. You either need to have a timer say for example receiver should listen for 1 hour- or make it available until program terminate. Either case you need to start your consumer program once:
Change your receiveJMS method as follows:
public void receiveJMS() throws NamingException, JMSException {
try{
ConnectionFactory connectionFactory = new ActiveMQConnectionFactory(ActiveMQConnection.DEFAULT_BROKER_URL);
Connection connection = connectionFactory.createConnection();
connection.start(); // it's the start point
Session session = connection.createSession(false,Session.AUTO_ACKNOWLEDGE);
// Getting the queue 'testQueue'
Destination destination = session.createQueue("testQueue");
MessageConsumer consumer = session.createConsumer(destination);
// set an asynchronous message listener
// JMSReceiver asyncReceiver = new JMSReceiver();
//no need to create another object
consumer.setMessageListener(this);
connection.setExceptionListener(this);
// connection.close(); once this is closed consumer no longer active
Thread.sleep(60 *60 * 1000); // receive messages for 1 hour
}finally{
connection.close();// after 1 hour close it
}
}
The above program will listen upto 1 hour. If you want it as long as the program run, remove the finally block. But the recommended way is to close it somehow. since your application seems to be standalone ,you can check the java runtime shutdown hook, where you can specify how to release such resources while program terminates.
If your consumer is a web application you can close it in a ServletContextlistner.

You aren't giving the consumer application any time to actually receive a message, you create it, then you close it. You either need to use a timed receive call to do an sync receive of the message from the Queue or you need to add some sort of wait in the main method such as a CountDownLatch etc to allow the async onMessage call to trigger shutdown once processing of the message is complete.

Restart embedded broker in unit test : VMTransportServer already bound

I'm trying to write a test that simulates a "broker down" phase.
Therefore I want to
start a local broker
send message1
stop the broker
send message2 (which will of course not arrive)
start the broker again
send message3
According to http://activemq.apache.org/how-do-i-restart-embedded-broker.html it is recommended to init a new BrokerService to start the broker again.
So the code looks (almost) like this:
private BrokerService _broker;
private void startBroker() throws Exception {
_broker = new BrokerService();
_broker.addConnector("vm://localhost?broker.persistent=false");
_broker.start();
_broker.waitUntilStarted();
}
private void stopBroker() throws Exception {
_broker.stop();
_broker.waitUntilStopped();
}
#Test
public void publishMessagesWithServerBreakdownInBetween()
throws Exception
{
startBroker();
... send and receive message (works fine)
stopBroker();
... send message (fails of course)
startBroker(); // this fails with java.io.IOException: VMTransportServer already bound at: vm://localhost?broker.persistent=false
... send and receive message
}
The problem is already mentioned as comment in code:
The restart of the broker fails due to the error : java.io.IOException: VMTransportServer already bound at: vm://localhost?broker.persistent=false
I found a similar problem at ActiveMQ forum (http://activemq.2283324.n4.nabble.com/VMTransportServer-already-bound-td2364603.html), but in my case the hostname isn't null.
Another idea was to set 2 different broker names, but that also didn't help.
What am I doing wrong?

You want to control what the VM Transport does by telling it not to try and create a broker for you since you are adding it to an already created broker. The rest is pretty simply then:
public class AMQRestartTest {
private BrokerService broker;
private String connectorURI;
private ActiveMQConnectionFactory factory;
#Before
public void startBroker() throws Exception {
createBroker(true);
factory = new ActiveMQConnectionFactory("failover://" + connectorURI);
}
private void createBroker(boolean deleteAllMessages) throws Exception {
broker = new BrokerService();
TransportConnector connector = broker.addConnector("vm://localhost?create=false");
broker.setPersistent(false);
broker.start();
broker.waitUntilStarted();
connectorURI = connector.getConnectUri().toString();
}
#Test(timeout = 60_000)
public void test() throws Exception {
Connection connection = factory.createConnection();
Session session = connection.createSession(false, Session.AUTO_ACKNOWLEDGE);
Queue queue = session.createQueue("test");
MessageConsumer consumer = session.createConsumer(queue);
MessageProducer producer = session.createProducer(queue);
connection.start();
broker.stop();
broker.waitUntilStopped();
createBroker(false);
producer.send(session.createTextMessage("help!"));
Message received = consumer.receive();
assertNotNull(received);
assertTrue(received instanceof TextMessage);
}
}

How to kill consumers in activemq

I am trying to get rid of all of the "Number of Consumers" in a certain queue. Whenever I purge/delete the queue, the number of consumers still remain if I ever create that queue with the same name again. Even with 0 pending messages, there are still 6 consumers.
My problem may have stemmed in my java code while not closing the session or connection.
I have tried both restarting and reinstalling the server.
Here is my producer code:
private static String url = ActiveMQConnection.DEFAULT_BROKER_URL;
public static String addElementToQueue(String queueName,String param1, String param2) throws JMSException, NamingException {
// Getting JMS connection from the server and starting it
ConnectionFactory connectionFactory =
new ActiveMQConnectionFactory(url);
Connection connection = connectionFactory.createConnection();
// JMS messages are sent and received using a Session. We will
// create here a non-transactional session object. If you want
// to use transactions you should set the first parameter to 'true'
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
// Destination represents here our queue on the
// JMS server. You don't have to do anything special on the
// server to create it, it will be created automatically.
Destination destination = session.createQueue(queueName);
// MessageProducer is used for sending messages (as opposed
// to MessageConsumer which is used for receiving them)
MessageProducer producer = session.createProducer(destination);
String queueMessage = param1+ "-" + param2;
TextMessage message = session.createTextMessage(queueMessage);
// Here we are sending the message!
producer.send(message);
connection.close();
session.close(); // added after problem came up
producer.close(); // added after problem came up
return commandID;
}
Here is my consumer code:
// URL of the JMS server
private static String url = ActiveMQConnection.DEFAULT_BROKER_URL;
public static Pair consumeNextElement(String queueName) throws JMSException {
// Getting JMS connection from the server
ConnectionFactory connectionFactory
= new ActiveMQConnectionFactory(url);
Connection connection = connectionFactory.createConnection();
connection.start();
// Creating session for seding messages
Session session = connection.createSession(false,
Session.AUTO_ACKNOWLEDGE);
// Getting the queue
Destination destination = session.createQueue(queueName);
// MessageConsumer is used for receiving (consuming) messages
MessageConsumer consumer = session.createConsumer(destination);
// Here we receive the message.
// By default this call is blocking, which means it will wait
// for a message to arrive on the queue.
Message message = consumer.receive();
// There are many types of Message and TextMessage
// is just one of them. Producer sent us a TextMessage
// so we must cast to it to get access to its .getText()
// method.
String[] parts = ((TextMessage)message).getText().split("-");
Pair retVal = new Pair(parts[0], parts[1]);
connection.close();
session.close(); // added after problem came up
consumer.close(); // added after problem came up
return retVal;
}
Any thoughts?
Thanks.

The number of consumers is the number of listeners on the queue. Purging the queue should only remove the enqueued messages - those consumers listening will be unaffected.
The ability of the consumer to maintain/re-establish a connection may depend on the transport used to connect, and settings for the transport may allow for some tweaking of connection properties.
I frankly don't have much experience with these, but you might investigate Advisory Messages as a means to help debug your connections. The JMX interface or web console don't appear to be helpful beyond reporting consumer counts.