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Message Driven Beans

Using JMS

Swapnil Shrivastava

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Challenges with RMI-IIOP

Performancemust wait while the serverperforms processing

ReliabilityWhen RMI-IIOP calls theserver, it has to be running

Support for multiple senders and receiversnot possible.

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Messaging

Receive messages from one or more

message producers and broadcast it to one

or more message consumers.

Support asynchronous programming.

Application

Message

Oriented

MiddlewareApplication

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Message Oriented Middleware

Software infrastructure that supports

messaging.

Example

Sonic MQ

IBM MQSeries

BEA Tuxedo/Q

Microsoft MSMQ

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Challenges addressed

PerformanceA messaging client does not needto block when performing a request.

ReliabilityIf your MOM supports guaranteed

delivery , you can send a message and know for

sure it will reach the destination, even if the

consumer is not available.

Support for multiple senders and receivers

possible..

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Messaging Domains

It is the style of messaging which is chosen

to send messages.

Types :

Publish/Subscribe (Pub/Sub) Domain.

Point-to-Point (PTP) Domain.

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Publish/Subscribe

Many message producers talking to many messageconsumers.

It is an implementation of distributed event drivenprocessing model.

Publisher send messages to topic in JMS.

Consumers who are interested in message

subscribe to message topic. Topic are persistent stores located at JMS

destination.

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Publish/Subscribe

Producer1

Producer 2 Consumer 2

Consumer 1Topic subscribe

deliver

subscribe

deliver

publishes

publishes

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Point-to-Point

Single consumer for each message.

Multiple producers can send messages to

the queue but each message is delivered tosingle consumer.

Messages are sent to queue from which they

are distributed to consumers in FIFO order. Queue are persistent stores located at JMS

destination.

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Point-to-Point

Producer Consumersends

acknowledges

consumes

Queue

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JMS

JMS is a messaging standard.

Allows applications to create,send ,receive and

read messages. JMS consists of

JMS API : to write code to send and receive messages.

JMS SPI : where we plug in JMS drivers.

Low level topology issues are abstracted from the

developer.

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JMS Programming Model

Locate JMS driver.

Create a JMS connection.

Create a JMS Session.

Locate a JMS destination.

Create a JMS producer or a JMS consumer.

Send or receive your message.

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JMS Architecture

Connection

FactoryConnection Session

Message

Consumer

Message

Producer

Message

Queue

or Topic

Queue

or Topic

creates creates

creates

creates

creates

Sends to

Gets

from

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JMS-EJB Integration

To allow EJB components to benefit from

value propositions of messaging such as

Non blocking clients

N-ary communication

EJB 2.0 introduced Message Driven Beans

for JMS-EJB Integration.

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Message Driven Beans

MDB is a special EJB component that can

receive JMS messages.

MDB consumes messages from queues ortopics that are sent by any valid JMS client.

JMS API is used to send messages to MDB.

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Message Driven

Bean Instance

Client JMS Destination

Message Driven

Bean Pool

Send/

publishes

EJB Server

Message Driven Beans

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MDB Characteristics

Doesnt have home interface, remote

interface,local interface and local home

interface. Have one loosely typed business method.

Do not have any return values.

Cannot send exceptions back to the client. They are stateless.

Can be durable or non durable subscribers.

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Message Driven Bean Interface

public interface javax.jms.MessageListener

{

public void onMessage(Message message);}

public interface javax.ejb.MessageDrivenBean extends EnterpriseBean

{

public void ejbRemove()throws EJBException;

public void setMessageDrivenContext(MessageDrivenContext ctx)

throws EJBException;

}

SCO

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MDB Ingredients

Message Driven Beans implements both

MessageDrivenBean and MessageListener

interface. Consistes of:

MessageDrivenBean class.

Deployment Descriptor.

Vendor Specific Files.

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Example

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MDB Object Model

java.io.Serializable

javax.ejb.EnterpriseBean

javax.ejb.MessageDrivenBean

Bean Implement

Class

Comes with Java2 platform

Comes with EJB Distribution

Written by developer

javax.jms.MessageListener

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Message Driven Bean Life Cycle

Does Not Exist

Pooled

1: newInstance()

2: setMessageDrivenContext()

3: ejbCreate()

ejbRemove()

onMessage()

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References

Mastering Enterprise Java Beans

J2EE 1.4 Tutorials

Professional Java Server Programming,

J2EE Edition