Module 10 Developing Java EE Applications using Messaging

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Module 10Developing Java EE Applications using Messaging

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272 Ω Omega ΩDeveloping Applications for Java EE Platform

Describe JMS API technology

Write a message producer

Write an asynchronous message consumer

Write a synchronous message consumer

List the capabilities and limitations of EJB components as messaging clients

Objectives

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Messaging System Participants

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Administered Objects

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Messaging Clients

The synchronous client blocks until a message arrives.

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Messages

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Point-to-Point Messaging Architecture

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Publish/Subscribe Messaging Architecture

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Creating a Queue Message Producer

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1. Obtain a connection factory using injection or the JNDIAPI.

2. Obtain the message queue using injection or the JNDI API.

3. Create a Connection object using the connection factory.

4. Create a Session object using the Connection object.

5. Create a QueueSender object using the Session object.

6. Create one or more Message objects using the Session object.


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7. Populate message with text using the setText method of the TextMessage object.

8. Send one or more Message objects using the QueueSender object.


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import javax.jms.*;import javax.naming.*;public class SimpleQSender

public static void main(String[] args) String queueName = null;Context jndiContext = null;QueueConnectionFactory queueConnectionFactory = null;QueueConnection queueConnection = null;QueueSession queueSession = null;Queue queue = null;QueueSender queueSender = null;TextMessage message = null;int NUM_MSGS = 5;

Example Code for Queue Message Producer

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// Read queue name from command line and display it.if (args.length != 1)

System.out.println("Usage: java SimpleQSender " +"<queue-name> ");

System.exit(1);queueName = new String(args[0]);System.out.println("Queue name is " + queueName);

try jndiContext = new InitialContext();

catch (NamingException e) System.out.println("Could not create JNDI API " +

"context: " + e.getMessage());System.exit(1);


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// Look up connection factory and queue. If either doestry

queueConnectionFactory = (QueueConnectionFactory)jndiContext.lookup("QueueConnectionFactory");queue = (Queue) jndiContext.lookup(queueName);

catch (NamingException e) System.out.println("JNDI API lookup failed: " +

e.getMessage());System.exit(1);

/** Create connection.* Create session from connection; false means session is* not transacted.* Create sender and text message.* Send messages, varying text slightly.* Send end-of-messages message.


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* Finally, close connection.*/try

queueConnection = queueConnectionFactory.createQueueConnection();

queueSession = queueConnection.createQueueSession(false,

Session.AUTO_ACKNOWLEDGE);queueSender = queueSession.createSender(queue);message = queueSession.createTextMessage();for (int i = 0; i < NUM_MSGS; i++)

message.setText("This is message " + (i + 1));System.out.println("Sending message: " +

message.getText());queueSender.send(message);


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// Send a non-text control message indicating end of// messages.queueSender.send(queueSession.createMessage());

catch (JMSException e) System.out.println("Exception occurred: " +

e.getMessage()); finally

if (queueConnection != null) try

Thread.sleep(60000); // delay before closingqueueConnection.close();

catch (JMSException e)


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@Resource(name="jms/QueueConnectionFactory")javax.jms.QueueConnectionFactory queueConnectionFactory;

@Resource(name="jms/someQueue")javax.jms.Queue queue;

An Alternative to JNDI Lookup:

Dependency Injection

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Synchronous Queue Consumer

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1. Obtain a connection factory using injection or the JNDI API.

2. Obtain the message queue using injection or the JNDI API.

3. Create a Connection object using the factory.

4. Create a Session object.

5. Create a MessageReceiver object.

6. Call the receive method of the MessageReceiverobject. The receive method blocks if the queue is empty.

7. Process the message returned by the receive method.

Synchronous Queue Consumer

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import javax.jms.*;import javax.naming.*;

public class SimpleQSender public static void main(String[] args)

String queueName = null;Context jndiContext = null;QueueConnectionFactory queueConnectionFactory = null;QueueConnection queueConnection = null;QueueSession queueSession = null;Queue queue = null;QueueReceiver queueReceiver = null;TextMessage message = null;

// Read queue name from command line and display it.if (args.length != 1)

System.out.println("Usage: java " +"SimpleQueueReceiver <queue-name>");

Example Code for Synchronous Queue Consumer

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System.exit(1);queueName = new String(args[0]);System.out.println("Queue name is " + queueName); try

jndiContext = new InitialContext(); catch (NamingException e)

System.out.println("Could not create JNDI API " +"context: " + e.getMessage());

System.exit(1); // Look up connection factory and queue. If either doestry

queueConnectionFactory = (QueueConnectionFactory)jndiContext.lookup("QueueConnectionFactory");

Example Code for Synchronous Queue ConsumerJa

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queue = (Queue) jndiContext.lookup(queueName); catch (NamingException e)

System.out.println("JNDI API lookup failed: " +e.getMessage());

System.exit(1);

/** Create connection.* Create session from connection; false means session is* not transacted.* Create receiver, then start message delivery.* Receive all text messages from queue until* a non-text message is received indicating end of* message stream.* Close connection.*/try


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queueConnection = queueConnectionFactory.createQueueConnection();

queueSession = queueConnection.createQueueSession(false,

Session.AUTO_ACKNOWLEDGE);queueReceiver = queueSession.createReceiver(queue);queueConnection.start();while (true)

Message m = queueReceiver.receive(1);if (m != null)

if (m instanceof TextMessage) message = (TextMessage) m;System.out.println("Reading message: " +

message.getText()); else break;

Example Code for Synchronous Queue ConsumerJa

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System.out.println("Exception occurred: " + e.getMessage());

finally if (queueConnection != null)

try queueConnection.close();



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1. Look up a connection factory using the JNDI API.

2. Look up the message queue using the JNDI API.

3. Create a Connection object using the factory.

4. Create a Session object.

5. Create a QueueReceiver object.

6. Call the setMessageListener method of theQueueReceiver object passing it an instance of aMessageListener interface.

7. Process the received message in the onMessage methodof the MessageListener instance.

Creating an Asynchronous Queue Consumer

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public class SimpleMessageListener implementsMessageListener

public void onMessage(Message message) TextMessage msg = null;try

if (message instanceof TextMessage) msg = (TextMessage) message;System.out.println("Reading message: " +

msg.getText()); else

System.out.println("Message of wrong type: " +message.getClass().getName());

catch (Exception e)

System.out.println("Exception in onMessage(): " +e.getMessage());

Example Code for Asynchronous Queue Consumer

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public static void main(String[] args) String queueName = null;Context jndiContext = null;QueueConnectionFactory queueConnectionFactory = null;QueueConnection queueConnection = null;QueueSession queueSession = null;Queue queue = null;QueueReceiver queueReceiver = null;TextMessage message = null;MessageListener listener = null;listener = new SimpleMessageListener();// Read queue name from command line and display it.if (args.length != 1)

System.out.println("Usage: java " +"SimpleQueueReceiver <queue-name>");

System.exit(1);

Example Code for Asynchronous Queue ConsumerJa

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queueName = new String(args[0]);System.out.println("Queue name is " + queueName); try

jndiContext = new InitialContext(); catch (NamingException e)

System.out.println("Could not create JNDI API " +"context: " + e.getMessage());

System.exit(1); // Look up connection factory and queue. If either doestry

queueConnectionFactory = (QueueConnectionFactory)jndiContext.lookup("QueueConnectionFactory");

queue = (Queue) jndiContext.lookup(queueName);


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catch (NamingException e) System.out.println("JNDI API lookup failed: " +

e.getMessage());System.exit(1);

/** Create connection.* Create session from connection; false means session is* not transacted.* Create receiver, then start message delivery.* Receive all text messages from queue until* a non-text message is received indicating end of* message stream.* Close connection.*/

Example Code for Asynchronous Queue ConsumerJa

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try queueConnection =

queueConnectionFactory.createQueueConnection();queueSession = queueConnection.createQueueSession(false,

Session.AUTO_ACKNOWLEDGE);queueReceiver = queueSession.createReceiver(queue);queueReceiver.setMessageListener(listener);queueConnection.start();

catch (JMSException e) System.out.println("Exception occurred:"+e.getMessage());

finally if (queueConnection != null)

try queueConnection.close();



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Evaluating the Capabilities and Limitations

of EJB Components as Messaging Clients

Enterprise Beans Producer SynchronousConsumer

AsynchronousConsumer

Session Bean Yes Not recommended Not possible

Message Driven Bean Yes Not recommended Yes

• Only message-driven beans can implement the

javax.jms.MessageListener interface.

• Entity and session beans participating in messaging are required to include the standard JMS API messaging producer or synchronous consumer code.

Module 10 Developing Java EE Applications using Messaging

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