Java Message Service JMS

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Java Message Service (JMS)

• Karteek Suvarna
• Hardik Vaishnav
• Nagaraju Medavarapu

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Introduction

• 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
• J2EE provides the following mechanisms for
  deferring work to the background
• JMS (Java Message Service)
• Message-Driven Beans (MDBs)

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JMS

• The JMS API provides a vendor-neutral standard
  programming interface for creating, sending, and
  receiving messages. JMS enables Java applications
  to asynchronously exchange messages containing
  data and events. JMS 1.1 is part of the J2EE 1.4
  standard.

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MDB

• Message-Driven Beans (MDBs) are EJBs that receive
  and process JMS messages. MDBs don't maintain
  state between invocations, so they resemble
  Stateless Session Beans. But MDBs differ from
  Stateless Session Beans
• MDBs differ from Stateless Session Beans in that
• A client is completely decoupled from an MDBthe
  client sends a JMS message and the MDB picks up
  the message.
• After sending a JMS asynchronously, the client
  doesn't wait for the MDB to receive the message.
  The client continues executing other business
  logic.

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JMS Architecture

• JMS Provider A messaging system that implements
  the JMS specification. A JMS Provider, also known
  as a JMS Server, routes messages between clients.
• Clients Java applications that send or receive
  JMS messages. A message sender is called the
  Producer, and the recipient is called a Consumer.
• Messages Messages contain data or events
  exchanged between Producers and Consumers.
• Destinations A Producer sends a message to a JMS
  Destination (either a Queue or a Topic), and the
  Consumer(s) listening on the JMS Destination
  receives the message.

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JMS Messaging Model
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Core JMS API

• Message Holds business data and routing
  information. Although you'll find several types
  of Messages, most of the time you'll use either a
  TextMessage (that contains textual data in its
  body) or an ObjectMessage (that holds
  serializable objects in its body).
• Destination Holds messages sent by the Producer
  to be received by the Consumer(s). A Destination
  is either a Queue or a Topic that the JMS Server
  manages on behalf of its clients.
• Connection Enables a JMS client to send or
  receive Messages. Use a Connection to create one
  or more Sessions.
• ConnectionFactory A ConnectionFactory is either
  a QueueConnectionFactory or it is a
  TopicConnectionFactory, depending on the
  messaging model, and it exists to create
  Connections.
• SessionA Session creates Producers, Consumers,
  and Messages. A Publish-Subscribe application
  uses a TopicSession, and a Point-to-Point
  application uses a QueueSession. Sessions are
  single-threaded.

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Application

• JAW Motors application needs to run a credit
  check on potential customers to pre-qualify them
  for car loans as part of the auto buying process.
• We need a way to defer the credit verification
  process to the background so the user can
  continue using the web site.

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JMS and Its Relationship to J2EE Transactions

• When you use JMS, you can participate in either
  distributed or local transactions
• Local transaction A local JMS transaction uses
  programmatic transaction management and only
  includes JMS messages in its transaction context.
  
• Distributed transaction A distributed
  transaction (or two-phase commit) uses the JTA
  for container-managed transactions that include
  JMS and other resources, including JDBC, EJBs

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Sending Messages with JMS

• To send JMS messages from the JAW Motors
  application, do the following
• Upgrade the web site
• Add a "Run Credit Check" link and form.
• Add a "Run Credit Check" action to the Controller
  Servlet.
• Add JMS
• Create an object that holds the user's credit
  information to send as a JMS message.
• Write a utility class to encapsulate sending a
  JMS message.
• Add JMS-based JNDI reference settings to the
  Web-based deployment descriptors (web.xml and
  jboss-web.xml).
• Automate JMS-based JNDI reference settings with
  XDoclet.
• Deploy a JMS Queue on JBoss with an MBean.

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Upgrade the Site Running a Credit Check

• We need to add a "Run Credit Check" link to the
  JAW Motors homepage

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JAW Motors Run Credit Check page

• When the user clicks on the "Run Credit Check"
  link, the Controller routes them to the Run
  Credit Checkpage

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ControllerServlet.java
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create a message
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Sending message

• pressing the "Submit Credit Info" from the "Run
  Credit Check" form invokes the Controller
  Servlet's runCreditCheck action. The Controller
  Servlet stores the user's credit information in
  the CreditCheckReqDTO and calls
  JmsProducer.sendMessage( ) to send the credit
  data as an asynchronous JMS message. After
  sending the message, the Controller Servlet
  returns the user to the main page.
• We've encapsulated the user's credit information
  in a CreditCheckRequestDTO

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Sending message
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ServiceLocator.java
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Web-Based Deployment DescriptorsWeb.xml

• ltres-ref-namegt is the JNDI name for each
  resourcejavacomp/env/jms/CreditCheckQueue and
  javacomp/env/jms/MyXAQueueConnectionFactory.
• The ltres-typegt for the CreditCheckQueue is a JMS
  Queue, and javax.jms.Queue is its fully qualified
  class name.
• The ltres-typegt for the Connection Factory is a
  JMS Queue Connection Factoryjavax.jms.QueueConnec
  tionFactory

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Web.xml

• lt?xml version"1.0" encoding"UTF-8"?gt
• ltweb-app xmlns"http//java.sun.com/xml/ns/j2ee"
• xmlnsxsi"http//www.w3.org/2001/XMLSchema-instan
  ce"
• xsischemaLocation"http//java.sun.com/xml/ns/j2e
  e
• http//java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
  version"2.4"gt
• ...
• ltresource-ref gt
• ltres-ref-namegtjms/CreditCheckQueuelt/res-ref-
  namegt
• ltres-typegtjavax.jms.Queuelt/res-typegt
• ltres-authgtContainerlt/res-authgt
• lt/resource-refgt
• ltresource-ref gt
• ltres-ref-namegtjms/MyXAQueueConnectionFactory
  lt/res-ref-namegt
• ltres-typegtjavax.jms.QueueConnectionFactorylt/
  res-typegt
• ltres-authgtContainerlt/res-authgt
• lt/resource-refgt
• ...

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jboss-web.xml

• lt?xml version"1.0" encoding"UTF-8"?gt
• lt!DOCTYPE jboss-web PUBLIC "-//JBoss//DTD Web
  Application 2.4//EN"
• "http//www.jboss.org/j2ee/dtd/jboss-web_4_0.dtd"gt
  
• ltjboss-webgt
• ...
• ltresource-refgt
• ltres-ref-namegtjms/CreditCheckQueuelt/res-ref-
  namegt
• ltjndi-namegtqueue/CreditCheckQueuelt/jndi-name
  gt
• lt/resource-refgt
• ltresource-refgt
• ltres-ref-namegtjms/MyXAQueueConnectionFactory
  lt/res-ref-namegt
• ltjndi-namegtjava/JmsXAlt/jndi-namegt
• lt/resource-refgt
• ...
• lt/jboss-webgt

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jboss-web.xml

• ltres-ref-namegt is the JNDI name for each
  resource.
• The textual value of each ltres-ref-namegt element
  in jboss-web.xml MUST match the value of the
  ltres-ref-namegt in web.xml. The Queue's
  ltjndi-namegt is the local JBoss-specific JNDI name
  that JBoss uses to deploy a JMS Queue.
• The Queue Connection Factory's ltjndi-namegt is the
  local JBoss-specific JNDI name that JBoss uses to
  deploy a JMS QueueConnectionFactory

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Message-Driven Beans (MDBs)

• A Message-Driven Bean (MDB) is an EJB whose sole
  purpose is to consume JMS messages. When a JMS
  producer sends a message to a JMS destination,
  the MDB listening on that destination receives
  the message and processes it. MDBs are pooled,
  stateless
• An MDB implements the JMS MessageListener
  interface its onMessage( ) method processes the
  message received from the JMS destination.
• Pooling enables concurrent behavior, so several
  instances of an MDB would run in parallel if
  multiple messages are in the queue or topic.

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Writing an MDB for JAW

• In the JAW Motors application, the
  CreditCheckProcessor is the MDB
• Consumes a JMS ObjectMessage that contains a
  CreditCheckRequestDTO
• The onMessage( ) method consumes a JMS message
  that contains the user's credit information, but
  we have to pull the CreditCheckRequestDTO out of
  the message before using it.
• we pass the CreditCheckRequestDTO to our external
  credit verification service. CreditVerificationSer
  vice.verifyCredit( )
• it returns a String value that tells whether the
  credit check passed or failed.

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CreditCheckProcessorBean.java
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MDB Transaction Settings

• Message-Driven Bean has two ways to manage
  transactions
• 1) Container-Managed Transactions (CMT)
• 2) Bean-Managed Transactions (BMT).
• BMT requires extra Java coding to handle
  transaction logic and forces the developer to
  manage the transaction
• CMT doesn't require you to handle transaction
  logic, pushes transaction settings into
  deployment descriptors.
• -uses JBoss transaction services
• There's no need to specify a transaction setting
  in the CreditCheckProcessor MDB because it
  doesn't participate in a transaction. The Bean's
  onMessage( ) method only sends an email message
  and doesn't do anything transactional (like
  updating a database).

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Deploying an MDB

• deploy it by adding information about the EJB
  (meta-data) to the J2EE standard (ejb-jar.xml)
  and JBoss (jboss.xml) EJB deployment descriptors.
  
• The new ltmessage-drivengt element describes.
• - About the bean class.
• - That it uses container-managed transactions
  (CMT).
• - That its Acknowledgment mode is
  Auto-acknowledge.
• - That it listens on a non-durable Queue

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ejb-jar.xml
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Jboss.xml
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Deploying an MDB

• In the ejb-jar.xml file you can only indicate
  that your MDB listens on a Queue, but there are
  no elements that associate the CreditCheckProcesso
  r MDB with the CreditCheckQueue. Since specifying
  the Queue name isn't part of the EJB
  specification
• we use the jboss.xml descriptor to associate an
  MDB with a JMS Destination. The ltmessage-drivengt
  element's ltdestination-jndi-namegt sub-element
  tells JBoss that the CreditCheckProcessor MDB
  listens on and receives messages from the
  CreditCheckQueue

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Automating MDB Deployment with XDoclet

• The _at_ejb.bean XDoclet tag generates the
  CreditCheckProcessor MDB's ltmessage-drivengt
  element and all its subelements in ejb-jar.xml.
• The _at_jboss.destination-jndi-name XDoclet tag
  generates the corresponding ltmessage-drivengt
  element in jboss.xml that indicates that the
  CreditCheckProcessor MDB listens for messages on
  the CreditCheckQueue

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CreditCheckProcessorBean.java

• /
• _at_ejb.bean name"CreditCheckProcessor"
• display-name"CreditCheckProcessorMDB"
• acknowledge-mode"Auto-acknowledge"
• destination-type"javax.jms.Queue"
• subscription-durability"NonDurable"
• transaction-type"Container"
• _at_jboss.destination-jndi-name
• name"queue/CreditCheckQueue"
• /
• public class CreditCheckProcessorBean implements
  MessageDrivenBean, MessageListener
• ...

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Questions?