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Java message service
 

Java message service

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    Java message service Java message service Document Transcript

    • Java Message Service – Quick learn (hopefully) Veeramani S vee.sam@live.comMessaging ?Messaging is one of the well known methods to integrate (communicate) two software components(applications).Major Benefits?Asynchronous : Either of the parties (sender or receiver) need not be available at the same time. I.e.sender can send a message as if the receiver is ready and waiting for the message even though actualreceiver is not active at the time of message sending. (Please note synchronous also possible)Reliable : Possible to make sure that one message is delivered once and only once. (E.g. A refundrequest to the customer should not processed more than one time)How ?Every message sent using JMS will be first received by the JMS Queue or Topic and will be available tillthe appropriate client consumes the message.JMS -API?JMS is JAVA API helps JAVA developers quickly build application with a capable of create, send orreceive message from/to any other application.Let us have some closer look:Terminologies :JMS Provider : Any vendor who is implementing the JMS API specificationJMS Client : Any Java application that creates, sends or receives messages using JMS implementation.Message : is object from JMS family used to communicate between JMS clients.Administered objects: Before stating our actual game there should be some infrastructure andcommonly agreed terms for the involved parties. (Destinations and connection factories) 1
    • A small story now:Figure 1 fictional scenario to depict asynchronous messaging and application integration using messagingSome discussion and clarification from hamazzzon.com story 1. Should the message server need not to be a standalone always? a. No it can be a part of hamazzzon.com application server or Fulfillment vendor application server also. 2. How long a message can wait in the message server? a. Administrator of the server can configure, default is 0 which means never expires till the message is consumed by a client 3. Can the same message be available after delivery to the Fulfillment vendor application? a. No, Strictly no dupes. Once and only once message will be delivered to the client. 4. How long a message can wait in the message server? a. Queues retain all messages sent to them until the messages are consumed or until the messages expire b. Administrator of the server can configure the expiry time, default is 0 which means never expires till the message is consumed by a client. 5. What happens if there is an exception? a. When an exception occurs while the message consumption message it will be marked as unread in the message server and will be ready to send for the next message lookup request. b. Also please note that it is possible to configure after certain number of attempts delivery failed message can be moved 2
    • to another message (so that hamazzzon can take a look on to it to fix and resend) or deleted permanently (in our story it is not wise) 6. How the message server determines that the message is consumed successfully by the client? a. Using the message acknowledge status. We will more about with sample code some time later. 7. Is it possible to include other operation in the same consume call and make it as a single transaction (For example vendor wants to update a database)? a. YES it is possible transaction support can be extended for this scenario 8. Is it possible to make the message sender to wait until a message consuming client pick up the message? a. YES it is possible through ACKNOWLWDGE_MODE setting (then it would turn as synchronous* call)LITTLE more concepts before we start our ROCKING code!In ancient days most of the MOM(Message Oriented Middleware) or messaging providers support oneof the following category but after the period JMS birth, most(all !) of the messaging providers startedsupporting both in single productPoint-to-PointIn this approach single message can be consumed by a single client. Consider our fulfillment story whichis really a point-to-point example, even if our hamazzzon.com has more than one fulfillment vendor onlyone of the vendor can/should do the fulfillment.In JMS call this approached message destination as Queue Figure 2 Point-to-Point (Queue)Publisher SubscriberIn this approach single message can be consumed by more than one client. Consider RBI (central bank)wants to send new rate of interest tariff to all the participant banks the same message has to beprocessed by all the banks subscribed.In JMS call this approached message destination as Topic 3
    • Figure 3 Publisher Subscriber (Topic)Some discussion from these concepts: 1. If there is more than one message consumption clients in what order message delivered to client? a. Whoever first calls the receive message method will the chance to consume b. However ordering can be defined in the message level so that server can decide which message should be delivered first. 2. Will all the consumer clients in the topic always get the message published in the Topic? a. NO. Only the clients online at the time of message publish will the chance to consume it. b. YES. By marking as durable consumer we can provide the capability to receive messages published while the consumer was not active. However this messages are limited from the time since durable consumer of a topic created 3. Is it guarantee that message every will be consumed at least once by its client in topic? a. No, for example if a topic has all non durable consumers and none of them active at the time of message publish then the message will not be processed by any client 4. Now it might sound little late question nevertheless, what actually I can send using JMS? a. TextMessage, MapMessage, BytesMessage, StreamMessage and ObjectMessage If you are not familiar with Administered objects configuration steps, you can get familiar using Weblogic server sample explained in this link. 4
    • Where is my code! Figure 4 JMS programming model 5
    • Message producer/sender clientimport javax.jms.Connection;import javax.jms.ConnectionFactory;import javax.jms.Destination;import javax.jms.JMSException;import javax.jms.MessageProducer;import javax.jms.Session;import javax.jms.TextMessage;import javax.naming.Context;import javax.naming.InitialContext;import javax.naming.NamingException;/** * @author sv * */public class TestJmsMessageSender { public static void main(String[] args) { Context jndiContext = null; ConnectionFactory connectionFactory = null; Connection connection = null; Session session = null; Destination dest = null; /* * Setting environment property, this should be ideally come form * properties files and should be set through HashMap, But it is * OK for our test run */ System.setProperty("java.naming.factory.initial", "weblogic.jndi.WLInitialContextFactory"); System.setProperty("java.naming.provider.url","t3://localhost:7001"); try { jndiContext = new InitialContext(); connectionFactory = (ConnectionFactory)jndiContext.lookup("jms/TestJmsConnectionFactory"); dest = (Destination)jndiContext.lookup("jms/TestJmsQueue"); /* * Create connection. Create session from connection; falsemeans * session is not transacted. */ connection = connectionFactory.createConnection(); 6
    • session =connection.createSession(false,Session.CLIENT_ACKNOWLEDGE); MessageProducer msgProducer = session.createProducer(dest); TextMessage message = session.createTextMessage(); message.setText("JMS TextMessage test......"); System.out.println("Sending message: " +message.getText()); msgProducer.send(message); System.out.println("Sending message: " +message.getText()); msgProducer.send(message); } catch (NamingException e) { e.printStackTrace(); } catch (JMSException e) { System.out.println("Exception occurred: " + e.toString()); } finally { if (connection != null) { try { connection.close(); } catch (JMSException e) { } } } }}Message Consumer/receiver clientimport javax.jms.Connection;import javax.jms.ConnectionFactory;import javax.jms.Destination;import javax.jms.JMSException;import javax.jms.MessageConsumer;import javax.jms.Queue;import javax.jms.QueueConnectionFactory;import javax.jms.Session;import javax.jms.TextMessage;import javax.naming.Context;import javax.naming.InitialContext;import javax.naming.NamingException;/** * @author sv * * */public class TestJmsMessageReceiver { 7
    • public static void main(String[] args) { Context jndiContext = null; ConnectionFactory connectionFactory = null; Connection connection = null; Session session = null; Destination dest = null; /* * Setting environment property */ System.setProperty("java.naming.factory.initial", "weblogic.jndi.WLInitialContextFactory"); System.setProperty("java.naming.provider.url","t3://localhost:7001"); try { jndiContext = new InitialContext(); connectionFactory = (QueueConnectionFactory)jndiContext.lookup("jms/TestJmsConnectionFactory"); dest = (Queue) jndiContext.lookup("jms/TestJmsQueue"); /* * Create connection. Create session from connection; falsemeans * session is not transacted. Create sender and textmessage. Send * messages, varying text slightly. Finally, closeconnection. */ connection = connectionFactory.createConnection(); session =connection.createSession(false,Session.CLIENT_ACKNOWLEDGE); connection.start(); MessageConsumer consumer = session.createConsumer(dest); TextMessage message = (TextMessage)consumer.receive(1000); System.out.println(message.getText()); message = (TextMessage) consumer.receive(1000); System.out.println(message.getText()); message.acknowledge(); //queueSession.commit(); } catch (NamingException e) { e.printStackTrace(); System.exit(1); } catch (JMSException e) { 8
    • System.out.println("Exception occurred: " + e.toString()); } catch(Exception e){ e.printStackTrace(); } finally { if (connection != null) { try { connection.close(); } catch (JMSException e) { } } } }}/! Trap zone : 1. Any acknowledge mode will be ignored if the transaction is enable in a session For example in the following code transaction flag is set as “true” hence whatever acknowledgement mode provided here will be ignored and set as “AUTO_ACKNOWLEDGE”, if the transaction succeeds then message will get automatically acknowledge ( using which means server will determine whether to remove the message or to redeliver). QueueSession queueSession createQueueSession(true,Session. CLIENT_ACKNOWLEDGE); 2. UserTransaction handling is allowed only for the MDBs configured as Bean-managed transactions a. For example messageDrivenContext.getUserTransaction().begin() will throw an exception if it called from a MDB which is configured as Container transitioned 3. MessageDrivenContext’s setRollbackOnly() would cause the server to re-deliver the message again. However this is legal only if the provider(connection factory) is XA transaction enabled 4. MDB acknowledge mode can either “Auto-Acknowledge” or “DUPS_OK_ACKNOWLEDGE” any other mode is not allowed 5. Throwing an exception in the onMessage() method of MDB make the server to re-deliver the message again 6. Security is depends on the provider and it’s a architectural decision.Exercise :Set a Topic in your application server and try a similar programTry to set up MDB and consume message send from a producer.In case of any clarification please contact me though my email, I will try to resolve. 9