A Simple Example of Synchronous Message Receives

This section describes the sending and receiving clients in an example that uses the receive method to consume messages synchronously. This section then explains how to compile, package, and run the clients using the GlassFish Server.

The following sections describe the steps in creating and running the example.

Writing the Clients for the Synchronous Receive Example

The sending client, producer/src/java/Producer.java, performs the following steps:

1. Injects resources for a connection factory, queue, and topic:

   @Resource(lookup = "jms/ConnectionFactory")
   private static ConnectionFactory connectionFactory;
   @Resource(lookup = "jms/Queue")private static Queue queue;
   @Resource(lookup = "jms/Topic")private static Topic topic;

2. Retrieves and verifies command-line arguments that specify the destination type and the number of arguments:

   final int NUM_MSGS;
   String destType = args[0];
   System.out.println("Destination type is " + destType);
   if ( ! ( destType.equals("queue") || destType.equals("topic") ) ) { 
       System.err.println("Argument must be \”queue\” or " + "\”topic\”");
       System.exit(1);
   }
   if (args.length == 2){ 
       NUM_MSGS = (new Integer(args[1])).intValue();
   } 
   else { 
       NUM_MSGS = 1;
   }

3. Assigns either the queue or topic to a destination object, based on the specified destination type:

   Destination dest = null;
   try { 
       if (destType.equals("queue")) { 
           dest = (Destination) queue; 
       } else { 
           dest = (Destination) topic; 
       }
   } 
   catch (Exception e) {
       System.err.println("Error setting destination: " + e.toString()); 
       e.printStackTrace(); 
       System.exit(1);
   }

4. Creates a Connection and a Session:

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

5. Creates a MessageProducer and a TextMessage:

   MessageProducer producer = session.createProducer(dest);
   TextMessage message = session.createTextMessage();

6. Sends one or more messages to the destination:

   for (int i = 0; i < NUM_MSGS; i++) { 
       message.setText("This is message " + (i + 1) + " from producer"); 
       System.out.println("Sending message: " + message.getText()); 
       producer.send(message);
   }

7. Sends an empty control message to indicate the end of the message stream:

   producer.send(session.createMessage());

   Sending an empty message of no specified type is a convenient way to indicate to the consumer that the final message has arrived.

8. Closes the connection in a finally block, automatically closing the session and MessageProducer:

   } finally { 
       if (connection != null) { 
           try { connection.close(); } 
           catch (JMSException e) { } 
       }
   }

The receiving client, synchconsumer/src/java/SynchConsumer.java, performs the following steps:

1. Injects resources for a connection factory, queue, and topic.

2. Assigns either the queue or topic to a destination object, based on the specified destination type.

3. Creates a Connection and a Session.

4. Creates a MessageConsumer:

   consumer = session.createConsumer(dest);

5. Starts the connection, causing message delivery to begin:

   connection.start();

6. Receives the messages sent to the destination until the end-of-message-stream control message is received:

   while (true) {
       Message m = consumer.receive(1); 
       if (m != null) { 
           if (m instanceof TextMessage) { 
               message = (TextMessage) m; 
               System.out.println("Reading message: " + message.getText()); 
           } else { 
               break; 
           } 
       }
   }

   Because the control message is not a TextMessage, the receiving client terminates the while loop and stops receiving messages after the control message arrives.

7. Closes the connection in a finally block, automatically closing the session and MessageConsumer.

The receive method can be used in several ways to perform a synchronous receive. If you specify no arguments or an argument of 0, the method blocks indefinitely until a message arrives:

Message m = consumer.receive();
Message m = consumer.receive(0);

For a simple client, this may not matter. But if you do not want your application to consume system resources unnecessarily, use a timed synchronous receive. Do one of the following:

• Call the receive method with a timeout argument greater than 0:

  Message m = consumer.receive(1); // 1 millisecond

• Call the receiveNoWait method, which receives a message only if one is available:

  Message m = consumer.receiveNoWait();

The SynchConsumer client uses an indefinite while loop to receive messages, calling receive with a timeout argument. Calling receiveNoWait would have the same effect.

Starting the JMS Provider

When you use the GlassFish Server, your JMS provider is the GlassFish Server. Start the server as described in Starting and Stopping the GlassFish Server.

To Create JMS Administered Objects for the Synchronous Receive Example

Creating the JMS administered objects for this section involves the following:

• Creating a connection factory

• Creating two destination resources

If you built and ran the simplemessage example in Chapter 17, A Message-Driven Bean Example and did not delete the resources afterward, you need to create only the topic resource.

You can create these objects using the Ant tool. To create all the resources, follow these steps.

1. In a terminal window, go to the producer directory:

   cd producer

2. To create all the resources, type the following command:

   ant create-resources

   To create only the topic resource, type the following command:

   ant create-topic

   These Ant targets use the asadmin create-jms-resource command to create the connection factory and the destination resources.

3. To verify that the resources have been created, use the following command:

   asadmin list-jms-resources

   The output looks like this:

   jms/Queue jms/Topic jms/ConnectionFactory Command list-jms-resources executed successfully.

Building, Packaging, Deploying, and Running the Clients for the Synchronous Receive Example

To run these examples using the GlassFish Server, package each one in an application client JAR file. The application client JAR file requires a manifest file, located in the src/conf directory for each example, along with the .class file.

The build.xml file for each example contains Ant targets that compile and package the example. The targets place the .class file for the example in the build/jar directory. Then the targets use the jar command to package the class file and the manifest file in an application client JAR file.

Because the examples use the common interfaces, you can run them using either a queue or a topic.

To Build and Package the Clients for the Synchronous Receive Example Using NetBeans IDE

1. In NetBeans IDE, select File->Open Project.

2. In the Open Project dialog, navigate to:

   tut-install/examples/jms/simple/

3. Select the producer folder.

4. Select the Open as Main Project check box.

5. Click Open Project.

6. In the Projects tab, right-click the project and select Build.

7. Select the synchconsumer folder.

8. Select the Open as Main Project check box.

9. Click Open Project.

10. In the Projects tab, right-click the project and select Build.

To Deploy and Run the Clients for the Synchronous Receive Example Using NetBeans IDE

1. Deploy and run the Producer example:

   1. Right-click the producer project and select Properties.

   2. Select Run from the Categories tree.

   3. In the Arguments field, type the following:

      queue 3

   4. Click OK.

   5. Right-click the project and select Run.

      The output of the program looks like this (along with some application client container output):

      Destination type is queue Sending message: This is message 1 from producer Sending message: This is message 2 from producer Sending message: This is message 3 from producer

      The messages are now in the queue, waiting to be received.

      ---

      Note –

      When you run an application client, there is usually a noticeable delay between the first two application client container messages and the remainder of the output.

      ---

2. Now deploy and run the SynchConsumer example:

   1. Right-click the synchconsumer project and select Properties.

   2. Select Run from the Categories tree.

   3. In the Arguments field, type the following:

      queue

   4. Click OK.

   5. Right-click the project and select Run.

      The output of the program looks like this (along with some application client container output):

      Destination type is queue Reading message: This is message 1 from producer Reading message: This is message 2 from producer Reading message: This is message 3 from producer

3. Now try running the programs in the opposite order. Right-click the synchconsumer project and select Run.

   The Output pane displays the destination type and then appears to hang, waiting for messages.

4. Right-click the producer project and select Run.

   The Output pane shows the output of both programs, in two different tabs.

5. Now run the Producer example using a topic instead of a queue.

   1. Right-click the producer project and select Properties.

   2. Select Run from the Categories tree.

   3. In the Arguments field, type the following:

      topic 3

   4. Click OK.

   5. Right-click the project and select Run.

      The output looks like this (along with some application client container output):

      Destination type is topic Sending message: This is message 1 from producer Sending message: This is message 2 from producer Sending message: This is message 3 from producer

6. Now run the SynchConsumer example using the topic.

   1. Right-click the synchconsumer project and select Properties.

   2. Select Run from the Categories tree.

   3. In the Arguments field, type the following:

      topic

   4. Click OK.

   5. Right-click the project and select Run.

      The result, however, is different. Because you are using a topic, messages that were sent before you started the consumer cannot be received. (See Publish/Subscribe Messaging Domain, for details.) Instead of receiving the messages, the program appears to hang.

7. Run the Producer example again. Right-click the producer project and select Run.

   Now the SynchConsumer example receives the messages:

   Destination type is topic Reading message: This is message 1 from producer Reading message: This is message 2 from producer Reading message: This is message 3 from producer

To Build and Package the Clients for the Synchronous Receive Example Using Ant

1. In a terminal window, go to the producer directory:

   cd producer

2. Type the following command:

   ant

3. In a terminal window, go to the synchconsumer directory:

   cd ../synchconsumer

4. Type the following command:

   ant

   The targets place the application client JAR file in the dist directory for each example.

To Deploy and Run the Clients for the Synchronous Receive Example Using Ant and the appclient Command

You can run the clients using the appclient command. The build.xml file for each project includes a target that deploys the client and then retrieves the client stubs that the appclient command uses. Each of the clients takes one or more command-line arguments: a destination type and, for Producer, a number of messages.

To build, deploy, and run the Producer and SynchConsumer examples using Ant and the appclient command, follow these steps.

To run the clients, you need two terminal windows.

1. In a terminal window, go to the producer directory:

   cd ../producer

2. Deploy the client JAR file to the GlassFish Server, then retrieve the client stubs:

   ant getclient

   Ignore the message that states that the application is deployed at a URL.

3. Run the Producer program, sending three messages to the queue:

   appclient -client client-jar/producerClient.jar queue 3

   The output of the program looks like this (along with some application client container output):

   Destination type is queue Sending message: This is message 1 from producer Sending message: This is message 2 from producer Sending message: This is message 3 from producer

   The messages are now in the queue, waiting to be received.

   ---

   Note –

   When you run an application client, there is usually a noticeable delay between the first two application client container messages and the remainder of the output.

   ---

4. In the same window, go to the synchconsumer directory:

   cd ../synchconsumer

5. Deploy the client JAR file to the GlassFish Server, then retrieve the client stubs:

   ant getclient

   Ignore the message that states that the application is deployed at a URL.

6. Run the SynchConsumer client, specifying the queue:

   appclient -client client-jar/synchconsumerClient.jar queue

   The output of the client looks like this (along with some application client container output):

   Destination type is queue Reading message: This is message 1 from producer Reading message: This is message 2 from producer Reading message: This is message 3 from producer

7. Now try running the clients in the opposite order. Run the SynchConsumer client:

   appclient -client client-jar/synchconsumerClient.jar queue

   The client displays the destination type and then appears to hang, waiting for messages.

8. In a different terminal window, run the Producer client.

   cd tut-install/examples/jms/simple/producer appclient -client client-jar/producerClient.jar queue 3

   When the messages have been sent, the SynchConsumer client receives them and exits.

9. Now run the Producer client using a topic instead of a queue:

   appclient -client client-jar/producerClient.jar topic 3

   The output of the client looks like this (along with some application client container output):

   Destination type is topic Sending message: This is message 1 from producer Sending message: This is message 2 from producer Sending message: This is message 3 from producer

10. Now run the SynchConsumer client using the topic:

    appclient -client client-jar/synchconsumerClient.jar topic

    The result, however, is different. Because you are using a topic, messages that were sent before you started the consumer cannot be received. (See Publish/Subscribe Messaging Domain, for details.) Instead of receiving the messages, the client appears to hang.

11. Run the Producer client again.

    Now the SynchConsumer client receives the messages (along with some application client container output):

    Destination type is topic Reading message: This is message 1 from producer Reading message: This is message 2 from producer Reading message: This is message 3 from producer