# JMS Load Balanced Clustered Queue Example

This example demonstrates a JMS queue deployed on two different nodes. The two nodes are configured to form a cluster.

We then create a consumer on the queue on each node, and we create a producer on only one of the nodes.

We then send some messages via the producer, and we verify that both consumers receive the sent messages in a round-robin fashion.

In other words, HornetQ load balances the sent messages across all consumers on the cluster

This example uses JNDI to lookup the JMS Queue and ConnectionFactory objects. If you prefer not to use JNDI, these could be instantiated directly.

Here's the relevant snippet from the server configuration, which tells the server to form a cluster between the two nodes and to load balance the messages between the nodes.

         <cluster-connection name="my-cluster">
            <address>jms</address>
            <connector-ref>netty-connector</connector-ref>
            <retry-interval>500</retry-interval>
            <use-duplicate-detection>true</use-duplicate-detection>
            <forward-when-no-consumers>true</forward-when-no-consumers>
            <max-hops>1</max-hops>
            <discovery-group-ref discovery-group-name="my-discovery-group"/>
         </cluster-connection>

For more information on HornetQ load balancing, and clustering in general, please see the clustering section of the user manual.

## Example step-by-step

To run the example, simply type `./build.sh` (or `build.bat` on windows) from this directory

1. Get an initial context for looking up JNDI from server 0.

       ic0 = getContext(0);

2. Look-up the JMS Queue object from JNDI

               Queue queue = (Queue)ic0.lookup("/queue/exampleQueue");

3. Look-up a JMS Connection Factory object from JNDI on server 0

               ConnectionFactory cf0 = (ConnectionFactory)ic0.lookup("/ConnectionFactory");

4. Get an initial context for looking up JNDI from server 1.

               ic1 = getContext(1);

5. Look-up a JMS Connection Factory object from JNDI on server 1

               ConnectionFactory cf1 = (ConnectionFactory)ic1.lookup("/ConnectionFactory");

6. We create a JMS Connection connection0 which is a connection to server 0

       connection0 = cf0.createConnection();

7. We create a JMS Connection connection1 which is a connection to server 1

       connection1 = cf1.createConnection();

8. We create a JMS Session on server 0

       Session session0 = connection0.createSession(false, Session.AUTO_ACKNOWLEDGE);

9. We create a JMS Session on server 1

       Session session1 = connection1.createSession(false, Session.AUTO_ACKNOWLEDGE);

10. We start the connections to ensure delivery occurs on them

       connection0.start();

       connection1.start();

11. We create JMS MessageConsumer objects on server 0 and server 1

       MessageConsumer consumer0 = session0.createConsumer(queue);

       MessageConsumer consumer1 = session1.createConsumer(queue);

12. We create a JMS MessageProducer object on server 0.

       MessageProducer producer = session0.createProducer(queue);

13. We send some messages to server 0.

    	final int numMessages = 10;

    	for (int i = 0; i < numMessages; i++)
    	{
    	   TextMessage message = session0.createTextMessage("This is text message " + i);

    	   producer.send(message);

    	   System.out.println("Sent message: " + message.getText());
    	}

14. We now consume those messages on *both* server 0 and server 1. We note the messages have been distributed between servers in a round robin fashion. HornetQ has load balanced the messages between the available consumers on the different nodes. HornetQ can be configured to always load balance messages to all nodes, or to only balance messages to nodes which have consumers with no or matching selectors. See the user manual for more details.
JMS Queues implement point-to-point message where each message is only ever consumed by a maximum of one consumer.

    	for (int i = 0; i < numMessages; i += 2)
    	{
    	   TextMessage message0 = (TextMessage)consumer0.receive(5000);

    	   System.out.println("Got message: " + message0.getText() + " from node 0");

    	   TextMessage message1 = (TextMessage)consumer1.receive(5000);

    	   System.out.println("Got message: " + message1.getText() + " from node 1");
    	}

15. And finally (no pun intended), always remember to close your JMS resources after use, in a `finally` block. Closing a JMS connection will automatically close all of its sessions, consumers, producer and browser objects

    	finally
    	{
    	   if (connection0 != null)
    	   {
    	      connection0.close();
    	   }

    	   if (connection1 != null)
    	   {
    	      connection1.close();
    	   }
    	}