Java Message Service (JMS)

1
Java Message Service (JMS)

• Karteek Suvarna
• Hardik Vaishnav
• Nagaraju Medavarapu

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Outline

• Basic Concepts
• API Programming Model
• Reliability Mechanisms
• Transactions in JMS
• Step by Step Sender/Receiver Application
• JMS Providers

3
What is JMS?

• A specification that describes a common way for
  Java programs to create, send, receive and read
  distributed enterprise messages
• loosely coupled communication
• Asynchronous messaging
• Reliable delivery
• Integration with J2EE
• Synchronous message send and receive
• Latest spec version is 1.1
• Part of J2EE 1.4

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Why use JMS?

• JMS vs. Vendor Specific APIs
• Abstraction from vendor specific APIs
• Message Oriented Middleware (MOM) vendors
  offer similar functionality and APIs
• Easy to upgrade components
• JMS vs. RPC
• Decoupled components
• Easy to replace components of the system
• Application does not require all components
  to be up and running
• Asynchronous messaging scales better
  when multiple
• systems need to be integrated

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RPC vs. JMS
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JMS Messaging Domains

• Point-to-Point (PTP)
• built around the concept of message queues
• each message has only one consumer
• Publish-Subscribe systems
• uses a topic to send and receive messages
• each message has multiple consumers

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Point-to-Point Messaging
Msg
Msg
consumes
Client1
Client2
Queue
sends
acknowledges
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Publish/Subscribe Messaging
subscribes
Client2
Topic
Msg
Client1
delivers
publishes
subscribes
Client3
delivers
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Message Consumptions

• Synchronously
• A subscriber or a receiver explicitly fetches the
  message from the destination by calling the
  receive method.
• The receive method can block until a message
  arrives or can time out if a message does not
  arrive within a specified time limit.
• Asynchronously
• A client can register a message listener with a
  consumer.
• Whenever a message arrives at the destination,
  the JMS provider delivers the message by calling
  the listener's onMessage() method.

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A JMS Application

• JMS Clients
• Java programs that send/receive messages
• Messages
• Administered Objects
• preconfigured JMS objects created by an admin for
  the use of clients
• ConnectionFactory, Destination (queue or topic)
• JMS Provider
• messaging system that implements JMS and
  administrative functionality

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JMS API Programming Model

• Administered Objects
• Connections
• Sessions
• Message Producers
• Message Consumers
• Messages

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Administered Objects

• Configured by the administrator
• Usually looked up through JNDI
• Connection Factories
• Used by the client to create a connection
• Has preconfigured parameters
• QueueConnectionFactory or TopicConnectionFactor
  y
• Destination Factories
• Where messages are put /read from
• Point To Point Queues
• Publish/Subscribe Topics

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JMS Administration
Administrative Tool
Bind
JNDI Namespace
Lookup
JMS Provider
JMS Client
Logical Connection
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JMS API Programming Model
Connection Factory
creates
Connection
Message Consumer
Message Producer
creates
creates
Session
receives from
sends to
creates
Destination
Destination
Msg
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Connections

• A virtual connection with a JMS provider
• Queue or Topic connections are created using the
• corresponding connection factory
• start needs to be called before messages can be
• consumed
• close needs to be called to release resources
• stop can be used to temporarily stop message
• delivery without closing the connection

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Sessions

• Single threaded context for consuming/producing
• messages
• Sessions are used to create message consumers,
• message providers, and messages
• Sessions provide a context to group as one
• atomic operation a number of sends and receives
• QueueSession and TopicSession
• Can be transactional (local)
• Can provide acknowledgment

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Message Producers

• Send messages to a destination
• Unidentified producers can be used when
• we want to specify the destination at send time
• QueueSender interface
• send
• TopicPublisher interface
• publish

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Message Consumers

• Receives messages sent to a destination
• Message Receivers
• QueueReceiver and TopicSubscriber
• start and close
• Used synchronously by calling the receive
  method
• Message Listeners
• QueueListener and TopicListener
• Used asynchronously (onMessage)
• Message Selectors
• Filter messages using an SQL92 conditional
  expression
• Only headers and properties can be filtered
  (not content)

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JMS Messages

• Message Header
• used for identifying and routing messages
• Unique ID, timestamp, destination, priority,
• Message Properties (optional)
• contains vendor-specified values, but could also
  contain application-specific data
• Message Body(optional)
• contains the data
• five different message body types in the JMS
  specification

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JMS Message Types
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Basic Reliability Mechanisms

• Controlling message acknowledgment
• Specifying message persistence
• Setting message priority levels
• Allowing messages to expire
• Creating temporary destinations
• Advanced JMS Reliability Mechanisms
• Creating durable subscriptions
• Using local transactions

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Acknowledgment Types

• Auto acknowledgment (AUTO_ACKNOWLEDGE)
• Message is considered acknowledged when
  successful
• return on MessageConsumer.receive() or
• MessageListener.onMessage()
• Client acknowledgment (CLIENT_ACKKNOWLEDGE)
• Client must call acknowledge() method of
  Message object
• Lazy acknowledgment (DUPS_OK_ACKNOWLEDGE)
• Messaging system acknowledges messages as
  soon as they are available for consumers

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Two Delivery Modes

• PERSISTENT delivery mode
• Default
• Instructs the JMS provider to take extra
• care to ensure that a message is not lost
• in transit in case of a JMS provider failure
• NON_PERSISTENT delivery model
• Does not require the JMS provider to store
• the message
• Better performance

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How to Specify Delivery Mode

• SetDeliveryMode method of the MessageProducer
  interface
• producer.setDeliveryMode
• (DeliveryMode.NON_PERSISTENT)
• Use the long form of the send or the publish
• method
• producer.send(message,
• DeliveryMode.NON_PERSISTENT, 3,10000)

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How to Set Delivery Priority

• Ten levels of priority range
• from 0 (lowest) to 9 (highest)
• Default is 4
• Use the setPriority method of the
  MessageProducer interface
• producer.setPriority(7)
• Use the long form of the send or the publish
  method
• producer.send(message,
• DeliveryMode.NON_PERSISTENT, 7, 10000)

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How Durable Subscription Works

• A durable subscription can have only one active
• subscriber at a time
• A durable subscriber registers a durable
  subscription by specifying a unique identity that
  is retained by the JMS provider
• Subsequent subscriber objects that have the same
  identity resume the subscription in the state in
  which it was left by the preceding subscriber
• If a durable subscription has no active
  subscriber, the JMS provider retains the
  subscription's messages until they are received
  by the subscription or until they expire

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More JMS Features

• Request/Reply
• by creating temporary queues and topics
• Session.createTemporaryQueue()
• producersession.createProducer(msg.getJMSReplyTo(
  ))
• reply session.createTextMessage(reply)
• reply.setJMSCorrelationID(msg.getJMSMessageID)
• producer.send(reply)
• Message selectors
• SQL-like syntax for accessing header
• subscriber session.createSubscriber(topic,
  priority gt 6 AND type alert )
• Point to point selector determines single
  recipient
• Pub-sub acts as filter

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Transactions in JMS

• Transaction scope is only between client
• and Messaging system not between clients
• a group of messages are dispatched as a unit
• (on the sender side)
• a group of messages are retrieved as a unit (on
• the receiver side)
• Local and Distributed transactions

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Local Transactions in JMS

• Local transactions are controlled by Session
• object
• Transaction begins when a session is created
• There is no explicit begin transaction
  method
• Transaction ends when Session.commit() or
• Session.abort() is called
• Transactional session is created by specifying
• appropriate flag when a session is created
• QueueConnection.createQueueSession(true, ..)
• TopicConnection.createTopicSession(true, ..)

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Distributed Transactions in JMS

• Coordinated by a transactional manager
• Applications will control the transaction via
• JTA methods
• Use of Session.commit() and Session.rollback()
  is
• forbidden
• Messaging operations can be combined with
  database transactions in a single transaction

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JMS API in a J2EE Application

• Since the J2EE1.3 , the JMS API has been an
  integral part of the platform
• J2EE components can use the JMS API to send
  messages that can be consumed asynchronously by a
  specialized Enterprise Java Bean
• message-driven bean

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MessageDriven Bean

• acts as a listener for the JMS, processing
  messages asynchronously
• specialized adaptation of the JMS API used in the
  context of J2EE applications

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JMS with EJB Example
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Steps for Building a JMS SenderApplication

• 1.Get ConnectionFactory and Destination object
• through JNDI
• 2.Create a Connection
• 3.Create a Session to send/receive messages
• 4.Create a MessageProducer
• 5.Start Connection
• 6.Send (publish) messages
• 7.Close Session and Connection

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(1) Locate ConnectionFactory andDestination
objects via JNDI

• // Get JNDI InitialContext object
• Context jndiContext new InitialContext()
• // Locate ConnectionFactory object via JNDI
• TopicConnectionFactory factory
• (TopicConnectionFactory) jndiContext.lookup(
• "MyTopicConnectionFactory")
• // Locate Destination object (Topic or Queue)
  through //JNDI
• Topic weatherTopic
• (Topic) jndiContext.lookup("WeatherData")

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(2) Create Connection Object

• // Create a Connection object from
• // ConnectionFactory object
• TopicConnection topicConnection
• factory.createTopicConnection()

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3) Create a Session

• // Create a Session from Connection object.
• // 1st parameter controls transaction
• // 2nd parameter specifies acknowledgment type
• TopicSession session
• topicConnection.createTopicSession (false,
• Session.CLIENT_ACKNOWLEDGE)

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4) Create Message Producer

• // Create MessageProducer from Session object
• // TopicPublisher for Pub/Sub
• // QueueSender for Point-to-Point
• TopicPublisher publisher
• session.createPublisher(weatherTopic)

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(5) Start Connection

• // Until Connection gets started, message flow
• // is inhibited Connection must be started
• // before messages will be transmitted.
• topicConnection.start()

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(6) Publish a Message

• // Create a Message
• TextMessage message session.createMessage()
• message.setText(My First JMS Application")
• // Publish the message
• publisher.publish(message)

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Steps for Building a JMS ReceiverApplication
(Asynchronous)

• 1.Get ConnectionFactory and Destination object
• (Topic or Queue) through JNDI
• 2.Create a Connection
• 3.Create a Session to send/receive messages
• 4.Create a MessageConsumer (TopicSubscriber or
• QueueReceiver)
• 5.Register MessageListener for non-blocking mode
• 6.Start Connection
• 7.Close Session and Connection

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4) Create Message Subscriber

• // Create Subscriber from Session object
• TopicSubscriber subscriber
• session.createSubscriber(weatherTopic)

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5) Register MessageListenerobject for
Asynchronous mode

• // Create MessageListener object
• WeatherListener myListener
• new WeatherListener()
• // Register MessageListener with
• // TopicSubscriber object
• subscriber.setMessageListener(myListener)

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Steps for Building a JMS ReceiverApplication
(Synchronous)

• 1.Get ConnectionFactory and Destination
• object (Topic or Queue) through JNDI
• 2.Create a Connection
• 3.Create a Session to send/receive messages
• 4.Create a MessageConsumer
• 5.Start Connection
• 6.Receive message
• 7.Close Session and Connection

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JMS Providers

• SunONE Message Queue (SUN)
• a JMS provider integrated with the SunONE
  Application Server
• http//www.sun.com
• MQ JMS (IBM)
• MQSeries is another messaging technology
• can configure MQ as a JMS provider
• (http//www7b.software.ibm.com/wsdd/library/techti
  p/0112_cox.html)

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JMS Providers

• WebLogic JMS (BEA)
• enterprise-class messaging system integrated into
  WebLogic Server
• http//dev2dev.bea.com/technologies/jms/index.jsp
• JMSCourier (Codemesh)
• merging C applications into a JMS environment
• http//www.codemesh.com/en/AlignTechnologyCaseStud
  y.html

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More JMS Vendors

• Fiorano Software http//www.fiorano.com
• JRUN Server http//www.allaire.com
• GemStone http//www.gemstone.com
• Nirvana http//www.pcbsys.com
• Oracle http//www.oracle.com
• A more exhaustive listing is available at
• http//java.sun.com/products/jms/vendors.html