Module 6 Message-Driven Beans. History Introduced in EJB 2.0 –Supports processing of asynchronous messages from a JMS provider Definition expanded in.

Module 6

Message-Driven Beans

History

• Introduced in EJB 2.0– Supports processing of asynchronous

messages from a JMS provider• Definition expanded in EJB 2.1

– Supports any messaging system• Annotations introduced in EJB 3.0

JMS and Message-Driven Beans

• All EJB 3.0 vendors must support a JMS provider

• JMS– Vendor neutral API used to access

enterprise messaging systems– Similar in concept to JDBC

JMS Terminology

• JMS Client– Applications that use JMS

• JMS Provider– System that handles routing and

delivery of messages• JMS Application

– Business system composed of many JMS clients and typically one JMS provider

• Producer– JMS client that sends a message

• Consumer– JMS client that receives a message

JMS in Action

• EJBs of all type can use JMS to send messages

• Messages consumed by other application or message-driven beans

Example using JMS

• TravelAgentBean

@Resource(mappedName=“ConnectionFactoryNameGoesHere”)private ConnectionFactory connectionFactory;

@Resource(mappedName=“TicketTopic”)private Topic topic;

@Removepublic TicketDO bookFlight (CreditCardDO card, double price)

throws IncompleteConversationalState {

if(customer == null || flight == null || seat == null)throw new IncompleteConversationalState();

Example using JMS

• TravelAgentBean

try {Reservation reservation = new Reservation(

customer, flight, seat, price, new Date());entityManager.persist(reservation);

process.byCredit(customer,card,price);TicketDO ticket = new TicketDO(customer, flight, seat, price);

Connection connect = connectionFactory.createConnection();Session session = connect.createSession(true,0);MessageProducer producer = session.createProducer(topic);TextMessage textMsg = session.createTextMessage();textMsg.setText(ticket.description);producer.send(textMsg);connect.close();

return ticket;} catch(Exception e) {

throw new EJBException(e);}

}

Message Types

• JMS Message is a Java Object– Header

•Delivery Information and Metadata– Message Body

•Text•Serializable Objects•Byte Streams•Other application data

Example using MapMessage

• TravelAgentBean

try {……TicketDO ticket = new TicketDO(customer, flight, seat,

price);……MessageProducer producer = session.createProducer(topic);MapMessage mapMsg = session.createMapMessage();mapMsg.setInt(“CustomerID”, ticket.customerID.intValue());mapMsg.setInt(“FlightID”, ticket.flightID.intValue());mapMsg.setInt(“SeatID”, ticket.seatID.intValue());mapMsg.setDouble(“Price”, ticket.price);producer.send(mapMsg);……

}

JMS is Asynchronous

• JMS client can send a message without having to wait for a reply

• Synchronous communication requires tight coupling between client and EJB

• Asynchronous communication decouples senders from receivers

JMS Messaging Models

• Publish-and-Subscribe (pub/sub)– One-to-Many broadcast– Topic– Push-based model

• Point-to-Point (p2p)– One-to-One delivery– Queue– Pull- or Polling-based model

Session Beans Should not Receive Messages

• Session beans (or entities) cannot be programmed to respond to JMS messages

• Can set up a business method that attempts to consume a JMS message but:– Method must be invoked

synchronously from EJB client– Method prone to blocking if no

message available• Bottom Line: Use Message-Driven

Beans instead!

Message-Driven Beans

• EJB– But no remote or local interface

• Stateless• Server-Side• Transaction-Aware• Processes Asynchronous Messages• Concurrent behavior because container

creates numerous instances

Message-Driven Bean

• ReservationProcessorBean

package edu.weber.reservationprocessor;import javax.jms.*;import edu.weber.domain.*;import edu.weber.processpayment.*;import edu.weber.travelagent.*;import java.util.Date;import javax.ejb.*;import javax.annotation.*;import javax.persistence.*;

@MessageDriven(activationConfig={@ActivationConfigProperty(

propertyName=“destinationType”,propertyValue=“javax.jms.Queue”),

@ActivationConfigProperty(propertyName=“messageSelector”,propertyValue=“MessageFormat=‘Version 3.4’”),

@ActivationConfigProperty(propertyName=“acknowledgeMode”,propertyValue=“Auto-acknowledge”)})

Message-Driven Bean

•ReservationProcessorBean

public class ReservationProcessBean implements javax.jms.MessageListener {

@PersistenceContext(unitName=“titanDB)private EntityManager em;

@EJBprivate ProcessPaymentLocal process;

@Resource(mappedName=“ConnectionFactory”)private ConnectionFactory connectionFactory;

Message-Driven Bean

• ReservationProcessorBean

public void onMessage(Message message) {try{

MapMessage reservationMsg = (MapMessage)message;

int customerPk = reservationMsg.getInt(“CustomerID”);int flightPk = reservationMsg.getInt(“FlightID”);int seatPk = reservationMsg.getInt(“SeatID”);double price = reservationMsg.getDouble(“Price”);

// get the credit card

Date expirationDate = new Date(reservationMsg.getLong(“CreditCardExpDate”);

String cardNumber = reservationMsg.getString(“CreditCardNum”);String cardType = reservationMsg.getString(“CreditCardType”);

CreditCardDO card = new CreditCardDO(cardNumber, expirationDate, cardType);

Message-Driven Bean

• ReservationProcessorBeanCustomer customer = em.find(Customer.class, customerPk);Flight flight = em.find(Flight.class, flightPk);Seat seat = em.find(Seat.class, seatPk);

Reservation reservation = new Reservation(customer, flight, seat, price, new Date());

em.persist(reservation);

process.byCredit(customer, card, price);

TicketDO ticket = new TicketDO(customer, cruise, cabin, price);

deliverTicket(reservationMsg, ticket);} catch (Exception e) {

throw new EJBException(e);}

}

MessageDrivenContext

• Extends EJBContext– No new methods added

Message-Driven Bean

• ReservationProcessorBeanpublic void deliverTicket(MapMessage reservationMsg, TicketDO ticket)

throws JMSException {

Queue queue = (Queue)reservationMsg.getJMSReplyTo();Connection connect =

connectionFactory.createConnection();Session session = connect.createSession(true, 0);MessageProducer sender =

session.createProducer(queue);ObjectMessage message =

session.createObjectMessage();message.setObject(ticket);sender.send(message);

connect.close();}

Message-Driven Bean Lifecycle

Does Not Exist

Method-ReadyPool

Message-Driven Bean Lifecycle

Does Not Exist

Method-ReadyPool

Class.newInstance()injections

@PostConstruct

Message-Driven Bean Lifecycle

Does Not Exist

Method-ReadyPool

@PreDestroy

Message-Driven Bean Lifecycle

Method-ReadyPool

BusinessMethods