Module 10 Developing Java EE Applications using Messaging

Transcription

1 Module 10 Developing Java EE Applications using Messaging Objectives 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 272 Ω Omega Ω 1

2 Messaging System Participants 273 Ω Omega Ω Administered Objects 274 Ω Omega Ω 2

3 Messaging Clients The synchronous client blocks until a message arrives. 275 Ω Omega Ω Messages 276 Ω Omega Ω 3

4 Point-to-Point Messaging Architecture 277 Ω Omega Ω Publish/Subscribe Messaging Architecture 278 Ω Omega Ω 4

5 Creating a Queue Message Producer 279 Ω Omega Ω Creating a Queue Message Producer 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 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. 280 Ω Omega Ω 5

6 Creating a Queue Message Producer 7. Populate message with text using the settext method of the TextMessage object. 8. Send one or more Message objects using the QueueSender object. 281 Ω Omega Ω Example Code for Queue Message Producer 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; 282 Ω Omega Ω 6

7 Example Code for Queue Message Producer // Read queue name from command line and display it. if (args.length!= 1) { System.out.println("Usage: java SimpleQSender " + "<queue-name> "); queuename = new String(args[0]); System.out.println("Queue name is " + queuename); jndicontext = new InitialContext(); catch (NamingException e) { System.out.println("Could not create JNDI API " + "context: " + e.getmessage()); 283 Ω Omega Ω Example Code for Queue Message Producer // Look up connection factory and queue. If either does queueconnectionfactory = (QueueConnectionFactory) jndicontext.lookup("queueconnectionfactory"); queue = (Queue) jndicontext.lookup(queuename); catch (NamingException e) { System.out.println("JNDI API lookup failed: " + e.getmessage()); /* * 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. 284 Ω Omega Ω 7

8 Example Code for Queue Message Producer * Finally, close connection. */ 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); 285 Ω Omega Ω Example Code for Queue Message Producer // 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) { Thread.sleep(60000); // delay before closing queueconnection.close(); catch (JMSException e) { 286 Ω Omega Ω 8

9 An Alternative to JNDI Lookup: Dependency javax.jms.queueconnectionfactory javax.jms.queue queue; 287 Ω Omega Ω Synchronous Queue Consumer 288 Ω Omega Ω 9

10 Synchronous Queue Consumer 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 MessageReceiver object. The receive method blocks if the queue is empty. 7. Process the message returned by the receive method. 289 Ω Omega Ω Example Code for Synchronous Queue Consumer 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>"); 290 Ω Omega Ω 10

11 Example Code for Synchronous Queue Consumer queuename = new String(args[0]); System.out.println("Queue name is " + queuename); jndicontext = new InitialContext(); catch (NamingException e) { System.out.println("Could not create JNDI API " + "context: " + e.getmessage()); // Look up connection factory and queue. If either does queueconnectionfactory = (QueueConnectionFactory) jndicontext.lookup("queueconnectionfactory"); 291 Ω Omega Ω Example Code for Synchronous Queue Consumer queue = (Queue) jndicontext.lookup(queuename); catch (NamingException e) { System.out.println("JNDI API lookup failed: " + e.getmessage()); /* * 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. */ 292 Ω Omega Ω 11

12 Example Code for Synchronous Queue Consumer 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; 293 Ω Omega Ω Example Code for Synchronous Queue Consumer catch (JMSException e) { System.out.println("Exception occurred: " + e.getmessage()); finally { if (queueconnection!= null) { queueconnection.close(); catch (JMSException e) { 294 Ω Omega Ω 12

13 Creating an Asynchronous Queue Consumer 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 the QueueReceiver object passing it an instance of a MessageListener interface. 7. Process the received message in the onmessage method of the MessageListener instance. 295 Ω Omega Ω Example Code for Asynchronous Queue Consumer public class SimpleMessageListener implements MessageListener { public void onmessage(message message) { TextMessage msg = null; 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()); 296 Ω Omega Ω 13

14 Example Code for Asynchronous Queue Consumer 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>"); 297 Ω Omega Ω Example Code for Asynchronous Queue Consumer queuename = new String(args[0]); System.out.println("Queue name is " + queuename); jndicontext = new InitialContext(); catch (NamingException e) { System.out.println("Could not create JNDI API " + "context: " + e.getmessage()); // Look up connection factory and queue. If either does queueconnectionfactory = (QueueConnectionFactory) jndicontext.lookup("queueconnectionfactory"); queue = (Queue) jndicontext.lookup(queuename); 298 Ω Omega Ω 14

15 Example Code for Asynchronous Queue Consumer catch (NamingException e) { System.out.println("JNDI API lookup failed: " + e.getmessage()); /* * 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. */ 299 Ω Omega Ω Example Code for Asynchronous Queue Consumer 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) { queueconnection.close(); catch (JMSException e) { 300 Ω Omega Ω 15

16 Evaluating the Capabilities and Limitations of EJB Components as Messaging Clients Enterprise Beans Producer Synchronous Consumer Asynchronous Consumer 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. 301 Ω Omega Ω 16