{"id":395,"date":"2018-07-27T11:39:47","date_gmt":"2018-07-27T11:39:47","guid":{"rendered":"http:\/\/csp12.epgpbooks.inflibnet.ac.in\/?post_type=chapter&p=395"},"modified":"2018-08-02T08:57:03","modified_gmt":"2018-08-02T08:57:03","slug":"jms-ii","status":"publish","type":"chapter","link":"https:\/\/ebooks.inflibnet.ac.in\/csp12\/chapter\/jms-ii\/","title":{"rendered":"JMS – II"},"content":{"raw":"Learning Objectives<\/strong>\r\n\r\n \r\n

In the previous module, we learnt about the JMS Messaging Model, Communication Model and Programming Models and some introduction about the JMS Messages. In this module, let us continue the exploration of JMS Messages, its types, formats and properties along with the illustration of a small JMS Sender and Receiver application. Also, we are going to learn the significance and need of Model View Controller.<\/p>\r\n\r\n

    \r\n \t
  1. JMS \u2013 Messages<\/strong><\/li>\r\n<\/ol>\r\n

    JMS application produces and consumes message.In the earlier module, we have seen about the five different types of messages along with a session object to create a message. Now, let us look through the functionality of JMS Message Producer and Message Consumer.<\/p>\r\n \r\n\r\n1.1 JMS \u2013 MessageProducer<\/strong>\r\n\r\n \r\n

    A Message Producer is an object created by a session and is used for sending messages to a destination.MessageProducer comes in two forms by implementing either the QueueSender or the TopicPublisher interface as shown in Figure 1.<\/p>\r\n \r\n

    \"\"<\/p>\r\n\r\n

    \r\n

    Here, we use the Session object to create a message producer.The following snippet shows how to create a message producer using either a queue sender or a topic publisher interface.<\/p>\r\n

    MessageProducer producer =session.createProducer (destination)<\/span><\/p>\r\n

    QueueSender queueSender = queueSession.createSender(queue);<\/span><\/p>\r\n

    TopicPublisher topicPublisher = topicSession.createPublisher(topic);<\/span><\/p>\r\n \r\n

    Once a message producer has been created, we can use it to send messages as shown below:<\/span><\/p>\r\n\r\n<\/div>\r\n

    \r\n\r\n\u00a0 \u00a0 \u00a0queueSender.send(message);\r\n\r\ntopicPublisher.publish(message);\r\n\r\n \r\n\r\n1.2 JMS \u2013 MessageConsumer<\/strong>\r\n\r\n \r\n

    A Message Consumer is an object that is created by a session and used for receiving messages sent to a destination. It is created by impleemnting the MessageConsumer interface.A message consumer allows a JMS client to register interest in a destination with a JMS provider. The JMS provider manages the delivery of messages from a destination to the registered consumers of the destination.The PTP form of message consumer implements the QueueReceiver interface and the publish\/subscribe form implements the TopicSubscriber interface.<\/p>\r\n \r\n

    For example, you may use a QueueSession to create a receiver for the queue myQueue, and you may use a TopicSession to create a subscriber for the topic myTopic as given below:<\/p>\r\n \r\n

    QueueReceiverqueueReceiver = queueSession.createReceiver(myQueue); TopicSubscribertopicSubscriber = topicSession.createSubscriber(myTopic); (OR)<\/p>\r\n \r\n

    TopicSubscribertopicSubscriber = TopicSession.createDurableSubscriber(myTopic); Once a message consumer has been created, it becomes active, and we can use it to<\/p>\r\n \r\n

    receive messages. With either a QueueReceiver or a TopicSubscriber, receive method can be used to consume a message synchronously. This method can be invoked at any time after calling the start method as given below:<\/p>\r\n \r\n\r\nqueueConnection.start();\r\n\r\nMessage m = queueReceiver.receive( );\r\n\r\n(OR)\r\n\r\ntopicConnection.start();<\/span>\r\n\r\nMessage m = topicSubscriber.receive(1000); \/\/ time out after a seccond.<\/span>\r\n\r\n \r\n\r\nIn order to consume a message asynchronously, a message listener need to be used. In synchronous message consumption, receive method can be used to consume a message synchronously. Similarly, this can be invoked at any time after calling the start method:<\/span>\r\n\r\n<\/div>\r\n

    \r\n\r\n \r\n\r\nqueueConnection.start();\r\n\r\nMessage m = queueReceiver.receive();\r\n\r\ntopicConnection.start();\r\n\r\nMessage m = topicSubscriber.receive(1000); \/\/ time out after a second\r\n\r\n \r\n

    In Asynchronous message consumption,<\/em><\/strong> message listeners and message selectors objects are included. A message listener is an object that acts as an asynchronous event handler for messages.This implements MessageListener Interface, which has only one method \u201conMessage(Message msg)\u201d. MessageListener is not specific to a particular destination. The \u201conMessage\u201d method is responsible for handling all exceptions too. The code snippet for setting a message listener for Topic is given below:<\/p>\r\n \r\n\r\nTopicListenertopicListener = new TopicListener(); topicSubscriber.setMessageListener(topicListener);\r\n\r\n \r\n

    Message selectors are used for filtering out the messages received by the application.Message selectors assign the work of filtering messages to the JMS provider rather than to the application.A message selector is a SQL92 String that contains an expression.A message selector cannot select messages on the basis of the content of the message body. Examples for Message Selector is given below:<\/p>\r\n \r\n\r\nExamples:<\/strong>\r\n\r\n \r\n\r\nphone LIKE \u2018223\u2019\r\n\r\nJMSType IS NOT NULL\r\n\r\nname = \u2018Tom\u2019\r\n\r\n \r\n\r\n1.3 JMS \u2013 Message Format<\/strong>\r\n\r\n \r\n

    The ultimate purpose of a JMS application is to produce and consume messages that can then be used by other software applications.JMS messages have a basic format that is simple but\u00a0highly flexible, allowing the users to create messages that match formats used by non-JMS applications on heterogeneous platforms.A JMS message consists of three parts:<\/span><\/p>\r\n\r\n<\/div>\r\n