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Java Message Service

Java Message Service. Sangeetha Chavala. What is Messaging?. Method of Communication between software components/applications peer-to-peer facility Not another Mail API!!!. Messaging System Concepts.

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Java Message Service

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  1. Java Message Service Sangeetha Chavala

  2. What is Messaging? • Method of Communication between software components/applications • peer-to-peer facility • Not another Mail API!!!

  3. Messaging System Concepts • Allows loosely coupled applications to communicate - contrast with RPC • Asynchronous • Reliable

  4. Messaging Systems Advantages • Platform &Network Location Independence • Flexibility • Scalability • Anonymity • Robustness • Asynchronous

  5. What is the JMS API? • A common JavaTM platform API for creating, sending, receiving and reading messages • Design Goals -Provides most of the functionality of common messaging systems -makes client applications portable across messaging products - Leverages Java Technology

  6. Common Models of Messaging • Point-to-Point • Publish/Subscribe

  7. Point-to-Point Messaging • Only one consumer of Queue Message • No timing dependencies between Sender and Receiver

  8. Publish/Subscribe Messaging • Broadcast Message to all Subscribers

  9. JMS Application • JMS Provider • JMS Clients • Messages • Administered Objects • Non-JMS Clients

  10. Messages Message Components • Header • Properties • Body

  11. Message Header • Used for Message Identification and Routing • Destination Field -includes Subject or Topic (for Pub/Sub) -queue(for point-to-point) • Also include other data -delivery mode -message ID -timestamp -priority -ReplyTo

  12. Message Properties • Application-specific properties • Messaging system provider-specific properties • Optional fields • Properties are Name/Value pairs • Values can be int, string, byte etc

  13. Message Body • Holds content of message • Five Types supported • Each type defined by a message interface -StreamMessage -MapMessage -BytesMessage -TextMessage -ObjectMessage

  14. Message Body Interfaces • StreamMessage -contains Java primitive values -Read sequentially • MapMessage -Holds name/value pairs -Read sequentially or by name • BytesMessage -uninterpreted bytes -used to match an existing message format

  15. Message Body Interfaces • TextMessage -contains java.util.StringBuffer -useful for XML messages • ObjectMessage -contains arbitrary java object -must be serializable

  16. Example:Creating a Text Message • To create a simple TextMessage: TextMessage message = session . createTextMessage( ); message . setText ( “greetings”);

  17. Building a JMS Client • Steps 1) Create a Connection to the provider 2) Create Sessions to send/receive messages 3) Create MessageProducers 4) Create MessageConsumers

  18. 1. Creating a Connection • Connection provides access to messaging system • Performs resource allocation and management • ConnectionFactory used to create Connection • ConnectionFactory is located through JNDI

  19. Get the Connection Factory Context messaging = new InitialContext ( ) ; TopicConnectionFactory factory = (TopicConnectionFactory) messaging . lookup ( “TopicConnectionFactory” ) ; • JNDI is used to get a ConnectionFactory • 2 Types ConnectionFactory - QueueConnectionFactory for P-to-P - TopicConnectionFactory for Pub/Sub

  20. Create the Connection TopicConnection topicConnection = factory . createTopicConnection ( ) ; • QueueConnection or TopicConnection

  21. 2. Create Sessions TopicSession session = topicConnection . createTopicSession (false, CLIENT_ACKNOWLEDGE); • First parameter controls transactions • Second parameter specifies message acknowledgement

  22. Locate a Topic Topic weatherTopic = messaging . Lookup ( “WeatherData” ) ; • JNDI is used to locate the topic • Queue or Topic

  23. Start the Connection topicConnection . start ( ) ; • During initialization, message flow is inhibited; Connection must now be started before messages will be transmitted

  24. 3. Create Message Producer TopicPublisher publisher = session . createPublisher (weatherTopic) ; • Publisher will publish messages to weathetData topic

  25. Publish a Message TextMessage message = session . createMessage ( ) ; message . setText ( “text : 35 degrees” ) ; publisher . Publish (message) ;

  26. Specifying Quality of Service Publish (Message message, int deliveryMode, int priority, long timeToLive) ; • Delivery Modes - NON-PERSISTENT - PERSISTENT • Priority • Time-to-Live

  27. 4. Message Consumer • Subscribing to topics - Durable Subscriptions - Non-durable Subsriptions • Receiving Messages - Asynchronous - Synchronous

  28. Asynchronous Message Receipt • Uses Listening Mechanism setMessageListener (MessageListener listener) • Listener object must implement onMessage ( ) of MessageListener interface

  29. Synchronous Message Receipt Message receive ( ) ; Message receive (long timeout) ; Message receiveNoWait ( ) ;

  30. Point-to-Point Programming • Queue Browsing - session . createBrowser (Queue queue); - session . createBrowser (QueueSession session, Queue queue, String messageSelector) ;

  31. JMS Programming Techniques and Issues 1. Transactions - commit( ) ; - rollback( ) ; with respect to producer with respect to consumer 2. Programmatic Message Acknowledgement acknowledge ( );

  32. JMS Programming Techniques and Issues 3. Message Routing - Routing via Hierarchical Topics bid_request bid_request.vehicles bid_request.vehicles.bicycle - Routing via Message Selection Property_MerchType = ‘Mountain Bike’ AND Property_ReqOvernight is NULL • Selecting a Routing Approach

  33. Using JMS to Transport XML StringBuffer body = new StringBuffer ( ) ; body.append (“?xml version=\”1.0\ “?>\n”) ; body.append (“<message>\n”); body.append (“<sender>”+username+“</sender>\n”) ; body.append (“<content>”+s+ “</content>\n”) ; body.append (“</message>\n”) ; msg.setText (body.toString( )) ; publisher . Publish (msg) ;

  34. Consuming XML Messages • Work with XML payload as a text stream • Work with the XML payload through the DOM • Use SAX to process the XML in an event-based manner

  35. Performing XML-based Routing - Use Message Properties • Request-Reply Programming - Replies are sent as full JMS message typically following some processing in the called ‘client’

  36. JMS Implementations • Standalone messaging servers • JMS services embedded within other environments such as an application server

  37. JMS and XML as an Integration Platform • Integration Types - Data Integration - Procedural or Process Integration • Messaging simplifies Application Integration - can’t use Objects - XML proves to be an optimal format

  38. Topics discussed • Messaging System Concepts • JMS Features • JMS Programming Techniques • JMS and XML as an Integration platform

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