J2EE JMS

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Java Messaging Service(JMS)

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Agenda

What is Messaging? Messaging models, Reliability, Transaction,

Distributed messaging, Security

Why Messaging?

What is JMS?

Architecture of JMS

JMS Programming APIs

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What is Messaging?

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Messaging System Concepts De-coupled (Loosely-coupled) communication

Asynchronous communication

Messages are the means of communicationbetween applications.

Underlying messaging software provides

necessary support MOM (Message Oriented Middleware), Messaging

system, Messaging server, Messaging provider,

JMS provider: they all mean this underlying

messaging software

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Messaging System Features

Support of two messaging models Point-to-point

Publish/Subscribe

Reliability

Transactional operations Distributed messaging

Security

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Additional Features

Some Messaging System vendorssupport

Guaranteed real-time delivery Secure transactions

Auditing

Metering Load balancing

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Messaging Models

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Messaging Models

Point to Point A message is consumed by a single

consumer

Publish/Subscribe A message is consumed by multiple

consumers

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Point-to-Point

A message is consumed by a singleconsumer

There could be multiple senders

"Destination" of a message is a namedqueue

First in, first out (at the same priority level)

Senders (producers) sends a message to anamed queue (with a priority level)

Receiver (consumer) extracts a message

from the queue

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Point-to-Point

QueueClient

Senders SendsConsumes

Acknowledges

ClientReceiver

Receives messages on

the queue

Posts messages to the

queue

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When to use Point-to-Point?

Use it when every message you sendmust be processed successfully by

one consumer

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Publish/Subscribe (Pub/Sub)

A message is consumed by multipleconsumers

"Destination" of a message is a namedtopic not a queue

Producers publish to topic

Consumers subscribe to topic

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Publish-and-Subscribe

ClientSender Sends

Consumes

Acknowledges

ClientReceiver

ClientPublishe

r

Publishes Topic

Clientsubscriber

Clientsubscriber

ClientPublishe

rTopic

Clientsubscriber

Clientsubscriber

Publishes

Subject ofcommunication

Available to registeredparticipants

Posts messages to thetopic

Receives messages

on the topic

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When to use Pub/Sub?

Use it when a message you sendneed to be processed by multiple

consumers Example: HR application

Create new hire topic

Many applications (facilities, payroll, etc.)subscribe new hire topic

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Reliability

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Reliability

Some guarantee of delivery of a message

Different degree of reliability is possible

Sender can specify different level of reliability Higher reliability typically means less throughput

Typically uses persistent storage forpreserving messages

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TransactionalOperations

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Transactional Operations

Transactional production Sender groups a series of messages into a

transaction

Either all messages are enqueuedsuccessfully or none are

Transactional consumption

Consumer retrieves a group of messages asa transaction

Unless all messages are retrievedsuccessfully, the messages remain in a

queue or topic

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Transactional Scope

Client-to-Messaging system scope Transaction encompasses the interaction

between each messaging client(applications) and the messaging system

JMS supports this

Client-to-Client scope

Transaction encompasses both clients JMS does not support this

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Client-to-Messaging System

Transactional Scope

Application 1 Queue Application 2

Messaging system

source: Applied Enterprise

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Client-to-Client

Transactional Scope

Application 1 Queue Application 2

Messaging system

source: Applied EnterpriseJavaBeans[1]

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DistributedMessaging

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Distributed Messaging

Enterprise messaging systems mightprovide an infrastructure in which

messages are being forwardedbetween servers called message channel

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Distributed Messaging

Application 1

Application 2

messa

ge

Queue

Queue

Messaging server

2

Messaging server 1

Message channel

messa

ge

source: Applied Enterprise JavaBeans[1]

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Security Issues

Authentication Messaging systems typically require clients to

present signed certificates

Confidentiality of messages Messaging system typically provide

encryption

Data integrity of messages Messaging system typically provide data

integrity through message digest

Security is currently handled in vendor-

specific way

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Why Messaging?

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Why Messaging?

Platform independence

Network location independence

Works well in heterogeneous environments

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Why Messaging?

Anonymity Whodoesnt matter

Wheredoesnt matter Whendoesnt matter

Contrast with RPC-based systems CORBA

RMI

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Why Messaging?

Robustness Receivers can fail.

Senders can fail. Network can fail.

Messaging System continues to function.

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Example MessagingApplications

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Messaging Applications

Credit card transactions

Weather reporting

Workflow Network management

Supply chain management

Customer care

Communications (Voice Over IP,Paging Systems, etc.)

Many more

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What is JMS?

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What is JMS?

JMS is a set of Java interfaces and associatedsemantics (APIs) that define how a JMS clientaccesses the facilities of a messaging system

Supports message production, distribution,delivery

Supported message delivery semantics

Synchronous or Asynchronous transacted

Guaranteed

Durable

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What is JMS? (Continued)

Supports existing messaging models Point-to-Point (reliable queue)

Publish/Subscribe

Message selectors (on the receiver side)

5 Message types

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JMS is an API

Java Application

JMS API

JMS

Provider

IBMMQSeries

JMS

Provider

ProgressSonicMq

JMS

Provider

Fiorano

JMS

Provider

JMS

Provider

BEA SUN MQ

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JMS and J2EE

Allows Java Developers to accessthe power of messaging systems

Part of the J2EE Enterprise Suite

JMS

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JMS Design Goals

Consistency with existing APIs

Independence from Messaging

system provider Minimal effort on part of Messaging

system provider

Provide most of the functionalityof common messaging systems

Leverage Java technology

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Architecture ofa JMS Application

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JMS Terminology

Domain (Messaging modes) point-to-point, publish/subscribe

Session Connection

Destination

Produce, send, publish Consume, receive, subscribe

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JMS Domains(Messaging Models)

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JMS Pub/Sub Non-durable vs.

JMS Pub/Sub Durable Non-durable

Messages are available only during the time

for which the subscriber is active If subscriber is not active (not connected), it

will miss any messages supplied in itsabsence

Durable Messages are retained on behalf of

subscribers that are not available at the timethe message was produced

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JMS Messages

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Messages

Messages are the means ofcommunication between messaging

applications Actual on-the-wire Message formats vary

widely among messaging systems A messaging system can interoperate with only

with the same messaging system

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Message Java Interface

JMS provides a unified and abstractmessage model via this interface

Actual object implementation of thisinterface is provider specific

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Message Header

Used for message identification androuting

Includes Destination

Also includes other data: delivery mode (persistent, nonpersistent)

message ID

timestamp priority

ReplyTo

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Message Header Fields

JMSDestination

JMSDeliveryMode

persistent or nonpersistent

JMSMessageID

JMSTimeStamp

JMSRedelivered JMSExpiration

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Message Body

Holds content of message

Several types supported

Each type defined by a messageinterface: StreamMessage

MapMessage

TextMessage

ObjectMessage

BytesMessage

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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 existingmessage format

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Example:

Creating Text Message To create a simple TextMessage:

TextMessage message =session.createTextMessage();

message.setText("greetings");

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Example:

Creating Object Message To create a simple ObjectMessage:

ObjectMessage message =

session.createObjectMessage();

message.setObject(myObject);

NOTE: myObjectmust implement

java.io.Serializable
http://java.io.serializable/http://java.io.serializable/http://java.io.serializable/

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JMS ProgrammingAPIs

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Connection Java Interface

An abstraction that represents a singlecommunication channel to JMS provider

Created from a ConnectionFactoryobject

A connection should be closed when theprogram is done using it.

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Connection Java Interface

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Session Java Interface

Created from a Connection object

Once connected to the provider via aConnection, all work occurs in thecontext of a Session

A session is single threaded, whichmeans that any message sending and

receiving happens in a serial order, oneafter the other

Sessions also provide a transactional

context

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Session Java Interface

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MessageProducer JavaInterface

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MessageConsumer JavaInterface Clients which want to receive messagescreate MessageConsumer object viaSession object

MessageConsumer object is attached toa Destination object

Client can receive messages in two

different modes Blocking

Non-blocking

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Receiving Messages in

Blocking mode Client calls receive() method ofMessageConsumer object

Client blocks until a message is available

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Receiving Messages in Non-

blocking mode Client registers a MessageListenerobject

Client does not block When a message is available, JMSprovider then calls onMessage() method

of the MessageListenerobject

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MessageConsumer JavaInterface

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JMS APIs

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JMS APIs

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(1) Locate ConnectionFactory andDestination objects via JNDI

// Get JNDI InitialContext objectContext jndiContext = new InitialContext();

// Locate ConnectionFactory object via JNDITopicConnectionFactory 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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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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(6) 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 MessageTextMessage message =

session.createMessage();message.setText("text:35 degrees");

// Publish the message

publisher.publish(message);

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Steps for Building a JMS Receiver

Application (non-blocking mode)1.Get ConnectionFactory and Destination

object (Topic or Queue) through JNDI

2.Create a Connection3.Create a Session to send/receive messages

4.Create a MessageConsumer (TopicSubscriberor QueueReceiver)

5.Register MessageListener for non-blockingmode

6.Start Connection

7.Close Session and Connection

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5) Register MessageListener

object for non-blocking mode// Create MessageListener objectWeatherListener myListener

= new WeatherListener();

// Register MessageListener with// TopicSubscriber objectsubscriber.setMessageListener(myListener);

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Steps for Writingblocking mode JMSReceiver Application

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Steps for Building a JMS Receiver

Application (non-blocking mode)1.Get ConnectionFactory and Destination

object (Topic or Queue) through JNDI

2.Create a Connection3.Create a Session to send/receive

messages

4.Create a MessageConsumer5.Start Connection

6.Receive message

7 Close Session and Connection

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How to Build RobustJMS Applications

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Most Reliable Way

The most reliable way to produce amessage is to send a PERSISTENTmessage within a transaction.

The most reliable way to consume amessage is to do so within atransaction, either from a queue or

from a durable subscription to a topic.

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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

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Advanced JMS ReliabilityMechanisms

Creating durable subscriptions

Using local transactions

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Controlling MessageAcknowledgment

Phases of Message

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Phases of MessageConsumption

The client receives the message

The client processes the message

The message is acknowledged Acknowledgment is initiated either by the

JMS provider or by the client, dependingon the session acknowledgment mode

Transaction And

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Transaction AndAcknowledgment

In transacted sessions Acknowledgment happens automatically

when a transaction is committed

If a transaction is rolled back, all consumedmessages are redelivered

In nontransacted sessions

When and how a message is acknowledgeddepend on the value specified (see nextslide) as the second argument of thecreateSession method

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Acknowledgment Types

Auto acknowledgment (AUTO_ACKNOWLEDGE)

Message is considered acknowledged when successfulreturn on MessageConsumer.receive() orMessageListener.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

H A k l d t T i

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How Acknowledgment Type is

set in JMS An acknowledge type is set when

Session is created by setting appropriate

flag QueueConnection.createQueueSession(..,)

TopicConnection.createTopicSession(.., )

ExampleTopicSession session =

topicConnection.createTopicSession (false,Session.CLIENT_ACKNOWLEDGE);

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Specifying MessagePersistence (DeliveryModes)

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Two Delivery Modes

PERSISTENT delivery mode Default

Instructs the JMS provider to take extra careto ensure that a message is not lost in transitin case of a JMS provider failure

NON_PERSISTENT delivery model

Does not require the JMS provider to storethe message

Better performance

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How to Specify Delivery Mode

SetDeliveryMode method of theMessageProducer interface producer.setDeliveryMode(DeliveryMode.NON

_PERSISTENT);

Use the long form of the send or thepublish method

producer.send(message,DeliveryMode.NON_PERSISTENT, 3,10000);

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Setting MessagePriority Levels

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Allowing Messages toExpire

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How to set Message Expiration

Use the setTimeToLive method of theMessageProducer interface producer.setTimeToLive(60000);

Use the long form of the send or thepublish method producer.send(message,

DeliveryMode.NON_PERSISTENT, 3,60000);

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Creating DurableSubscriptions

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Maximum Reliability

To ensure that a pub/sub applicationreceives all published messages Use PERSISTENT delivery mode for the

publishers In addition, use durable subscriptions for the

subscribers

Use the

Session.createDurableSubscribermethod to create a durable subscriber

How Durable Subscription

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How Durable SubscriptionWorks A durable subscription can have only one active

subscriber at a time

A durable subscriber registers a durablesubscription 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 inwhich it was left by the preceding subscriber

If a durable subscription has no active subscriber,the JMS provider retains the subscription'smessages until they are received by thesubscription or until they expire

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Transactions in JMS

T i i JMS

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Transactions in JMS

Transaction scope is only betweenclient and Messaging system notbetween 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

L l T i i JMS

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Local Transactions in JMS

Local transactions are controlled by Sessionobject

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 specifyingappropriate flag when a session is created QueueConnection.createQueueSession(true, ..)

TopicConnection.createTopicSession(true, ..)

Di ib d T i i JMS

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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 singletransaction

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MessageSelector

JMS M S l t

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JMS Message Selector

(Receiver) JMS application uses aselector to select only the messagesthat are of interest

A selector is essentially a SQL92string that specifies selection (orfiltering) rule A Teller object listening for Account objects

as messages may be required to dosomething only when the account balancedrops below a $1000

Example: JMS Message

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Example: JMS MessageSelectors The selector cannot reference the

contents of a message

It can access the properties and header

Examples JMSType==wasp

phone LIKE 223

price BETWEEN 100 AND 200 name IN(sameer,tyagi)

JMSType IS NOT NULL

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Messaging Featuresnot Defined in JMS

Messaging Features Not

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Messaging Features Not

Defined in JMS (No APIs) Encryption

JMS spec assumes messaging system

handles it Access control

JMS spec assumes messaging systemhandles it

Load balancing

Administration of queues and topics

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JMS and Message-Driven Bean (MDB)

JMS d MDB

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JMS and MDB

JMS ProviderEJB Container

Destin-ation

Consumer

Instances

Msg-drivenBean Class

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Documents

J2EE JMS