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 private ConnectionFactory private Topic public 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.*; propertyName=“destinationType”, propertyName=“messageSelector”, propertyValue=“MessageFormat=‘Version propertyName=“acknowledgeMode”, propertyValue=“Auto-acknowledge”)})

Message-Driven Bean ReservationProcessorBean public class ReservationProcessBean implements javax.jms.MessageListener private EntityManager private ProcessPaymentLocal 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 ReservationProcessorBean Customer 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 ReservationProcessorBean public 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-Ready Pool

Message-Driven Bean Lifecycle Does Not Exist Method-Ready Pool Class.newInstance()

Message-Driven Bean Lifecycle Does Not Exist Method-Ready

Message-Driven Bean Lifecycle Method-Ready Pool Business Methods