Module 5

Session Beans

Session Beans

Topics to be Covered:• Purpose and Types of Session Beans• Stateless Session Beans• Stateful Session Beans• Session Bean Design• Deployment Descriptor Structure

Session Beans

Purpose and Types

of Session Beans

Entities vs. Session Beans

• Entities– Object-Oriented interface for data

access– Define business logic around a

concept– Encourages reuse

• Session Beans– Describe workflow by managing

interactions among other beans– Implement tasks– Perform data access directly or

through entities

Data Access and Workflow

• Data Access– Span concepts– Read only

• Workflow– Combines the representative

concepts defined by entities •Booking a room in a hotel•Renting a video

Stateless and Stateful Session Beans

• Stateless Session Bean– Collection of related services

(methods)– No state preserved between method

invocations– General purpose and reusable

• Stateful Session Bean– Extension of the client– Maintains conversational state

• Both types of Session Beans are NOT persistent

Stateful Session Beans

• Conversational state is shared among all methods in the beans

• Specific to one scenario• Represent process logic• Could have a timeout• Can be removed

– Bean instance is destroyed– EJB object is invalidated

Stateless Session Beans

• Not dedicated to one client– Participate in an instance pool– Can be reassigned to another EJB

object– Does not distinguish between clients

• Could have a timeout• Can be removed

– Bean instance is NOT destroyed– EJB object is invalidated

Session Beans

StatelessSession Bean

A Wandering Bean

• Lightweight and fast• Efficient• Easy to develop• Swapped freely between EJB objects

– Overhead of swapping reduced•Does not require passivation or activation

A Forgetful Bean

• Provides one-shot services (methods)– Generic and reusable– Not interdependent– All information passed in method

parameters• Traditional transaction processing

application– Procedure executes– No state retained

• Possible uses include– Report generation– Stock quotes– Validating Credit Cards

An Unreliable Bean

• Internal state may be maintained– Number of times bean is called– Debugging information– Reference to a live resource

• Internal state NOT visible from client– Different instances may service

different requests– Values will change randomly

Stateless Session Bean Example

• Business interface: ProcessPayment

package edu.weber.processpayment;import edu.weber.domain.Customer;

public interface ProcessPayment {

public boolean byCheck(Customer customer, CheckDO check, double amount) throws PaymentException;

public boolean byCash(Customer customer, double amount) throws PaymentException;

public boolean byCredit(Customer customer, CheckCardDO card, double amount) throws PaymentException;

}

Stateless Session Bean Example

• Remote Interface

package edu.weber.processpayment;import javax.ejb.Remote;

@Remotepublic interface ProcessPaymentRemote extends ProcessPayment {}

• Local Interface

package edu.weber.processpayment;import javax.ejb.Local;

@Localpublic interface ProcessPaymentLocal extends ProcessPayment {}

Stateless Session Bean Example

• Credit Card Domain Object

package edu.weber.processpayment;import java.util.Date;

public class CreditCardDO implements java.io.Serializable {final static public String MASTER_CARD = “MASTER_CARD”;final static public String VISA = “VISA”;

public String number;public Date expiration;public String type;

public CreditCardDO(String numbr, Date exp, String typ) {number = numbr;expiration = exp;type = typ;

}}

Stateless Session Bean Example

• Check Domain Object

package edu.weber.processpayment;

public class CheckDO implements java.io.Serializable {public String checkBarCode;public int checkNumber

public CheckDO(String barCode, int number) {checkBarCode = barCode;checkNumber = number;

}}

Stateless Session Bean Example

• Application Exceptions– Should describe a business logic

problem– Should be meaningful to the client– Problem is possibly recoverable– Do not cause a transaction rollback– EJB container treats any exception that

does not extend RuntimeException as an application exception

– Propagated to the calling client as-is– Instance variables of the exception

should be serializable

Stateless Session Bean Example

• EJBException– Extends RuntimeException

(Unchecked)– Implies an unrecoverable problem– Non-application exceptions are

always wrapped in an EJBException by the EJB container

– Subsystem checked exceptions like NamingException and SQLException should typically be caught and wrapped in an EJBException

– All exceptions thrown by Java Persistence interfaces are RuntimeExceptions

Stateless Session Bean Example

• ProcessPaymentBean

package edu.weber.processpayment;import edu.weber.domain.*;

import java.sql.*;import javax.ejb.*;import javax.annotation.Resource;

import javax.sql.DataSource;import javax.ejb.EJBException;

@Statelesspublic class ProcessPaymentBean

implements ProcessPaymentRemote, ProcessPaymentLocal {

final public static String CASH = “CASH”;final public static String CREDIT = “CREDIT”;final public static String CHECK = “CHECK”;

Stateless Session Bean Example

• ProcessPaymentBean

@Resource(mappedName=“java:/DefaultDS”) DataSource dataSource;@Resource(name=“min”) int minCheckNumber;

public boolean byCash(Customer customer, double amount)throws PaymentException {return process(customer.getId(), amount, CASH, null, -1, null,

null);}

public boolean byCheck(Customer customer, CheckDO check, double amount) throws PaymentException {

if(check.checkNumber > minCheckNumber) {return process(customer.getId(), amount, CHECK, check.checkBarCode,

check.checkNumber, null, null);} else {

throw new PaymentException(“Check number is too low. Must be at least “ + minCheckNumber);}

}

Stateless Session Bean Example

• ProcessPaymentBean

public boolean byCredit(Customer customer, CreditCardDO card, double amount) throws PaymentException {

if(card.expiration.before(new java.util.Date())) {throw new PaymentException(“Expiration data has passed”);} else {

return process(customer.getId(), amount, CREDIT, null -1, card.number, new java.sql.Date(card.expiration.getTime()));}

}

Stateless Session Bean Example

• ProcessPaymentBeanpublic boolean process(int customerID, double amount, String type,String checkBarCode, int checkNumber, String creditNumber,java.sql.Date creditExpDate) throws PaymentException {

Connection con = null;PreparedStatement ps = null;

try {con = dataSource.getConnection();ps = con.prepareStatement (“INSERT INTO payment (customer_id,amount,type,” +

“check_bar_code,check_number,credit_number,”+“credit_exp_date) VALUES(?,?,?,?,?,?,?)”);

ps.setInt(1,customerID);ps.setDouble(2,amount);ps.setString(3,type);ps.setString(4,checkBarCode);ps.setInt(5,checkNumber);ps.setString(6,creditNumber);ps.setDate(7,creditExpDate);int retVal = ps.executeUpdate();if(retVal != 1) {

throw new EJBException(“Payment insert failed”);}return true;

}

Stateless Session Bean Example

• ProcessPaymentBean

catch(SQLException sql) {throw new EJBException(sql);

} finally {try {if(ps != null) ps.close();if(con != null) con.close();

}catch(SQLException se) {se.printStackTrace();

} } // finally} // process method

} // ProcessPaymentBean class

Stateless Session Bean Example

• Injection – Accessing Environment Properties

<ejb-jar xmlns=http://java.sun.com/xml/ns/javaee xmlns:xsi=http://www.w3.org/2001/XMLSchema-instance xsi:schemaLocation=“http://java.sun.com/xml/ns/javaee

http://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd” version=“3.0”>

<enterprise-beans><session>

<ejb-name>ProcessPaymentBean</ejb-name><env-entry> <env-entry-name>min</env-entry-name> <env-entry-type>java.lang.Integer</env-entry-type> <env-entry-value>250</env-entry-value></env-entry>

</session></enterprise-beans>

</ejb-jar>

SessionContext

• Provides a view into the EJB container’s environment

• Extends javax.ejb.EJBContext

@Statelesspublic class A_Bean implements A_BeanRemote {

@Resource private SessionContext context;

public void someMethod() {

B_BeanRemote b = …// Get a remote reference to B_BeanA_BeanRemote mySelf =

context.getBusinessObject(A_BeanRemote.class);

b.aMethod( mySelf );…

}}

Stateless Session Bean Lifecycle

Does Not Exist

Method-ReadyPool

Stateless Session Bean Lifecycle

Does Not Exist

Method-ReadyPool

Class.newInstance()injections

@PostConstruct

Stateless Session Bean Lifecycle

Does Not Exist

Method-ReadyPool

@PreDestroy

Stateless Session Bean Lifecycle

Method-ReadyPool

BusinessMethods

Session Beans

StatefulSession Bean

A Loyal Bean

• Dedicated to one client• Not swapped or pooled

StatefulSessionBean

remoteinterface

EJB objectremoteinterface

EJB objectstub

Client Container

An Attentive Bean

• Maintains conversational state– Methods can be interdependent– State predictable from one call to the

next• Not persistent • Not used concurrently

A Representative Bean

• Agent for the client• Off loads logic on to the server

– Provides for thin client• Encapsulates and Manages processes

and workflow– Presents a simplified interface to the

client– Minimizes network traffic– Minimizes number of connections

Stateful Session Bean Example

• Remote interface: TravelAgentRemote

package edu.weber.travelagent;import edu.weber.processpayment.CreditCardDO;import javax.ejb.Remote;import edu.weber.domain.Customer;

@Remotepublic interface TravelAgentRemote {

public Customer findOrCreateCustomer(String first, String last);public void updateAddress(Address addr);public void setFlightID(int flight);public void setSeatID(int seat);public TicketDO bookFlight(CreditCardDO card, double price)

throws IncompleteConversationalState;

}

Stateful Session Bean Example

• Application Exception: IncompleteConversationalState

package edu.weber.travelagent;

public class IncompleteConversationalState extends java.lang.Exception {

public IncompleteConversationalState() { super(); }public IncompleteConversationalState(String msg) {super(msg);}

}

Stateful Session Bean Example

• Domain Object: TicketDO

package edu.weber.travelagent;

public class TicketDO implements java.io.Serializable {

// Packages Customer, FlightID, SeatID, price, and description// as a POJO

}

Stateful Session Bean Example

• Ensure Session Bean interface can satisfy a typical client scenario:– Look up TravelAgent EJB– Locate an existing customer or create

a new customer– Get address changes or information– Gather flight and seat information– Collect credit card information– Determine price– Complete reservation by Booking the

Flight

Stateful Session Bean Example

• TravelAgentBean

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

@Statefulpublic class TravelAgentBean implements TravelAgentRemote {

@PersistenceContext(unitName=“titan)private EntityManager entityManager;

@EJB private ProcessPaymentLocal processPayment;

Stateful Session Bean Example

• TravelAgentBean

private Customer customer;private Flight flight;private Seat seat;

public Customer findOrCreateCustomer(String first, String last) {try {

Query q = entityManager.createQuery(“select c ” + “from Customer c ” + “where c.firstName = :first and c.lastName = :last”);q.setParameter(“first”, first);q.setParameter(“last”, last);this.customer = (Customer)q.getSingleResult();} catch (NoResultException notFound) {

this.customer = new Customer();this.customer.setFirstName(first);this.customer.setLastName(last);entityManager.persist(this.customer);

}return this.customer;

}

Stateful Session Bean Example

• TravelAgentBean

public void updateAddress(Address addr) {this.customer.setAddress(addr);this.customer = entityManager.merge(customer);

}

Stateful Session Bean Example

• TravelAgentBean

public void setSeatID (int seatID) {this.seat = entityManager.find(Seat.class, seatID);if(seat == null) throw new NoResultException(“Seat not found”);

}

public void setFlightID (int flightID) {this.flight = entityManager.find(Flight.class, flightID);if(flight == null) throw new NoResultException(“Flight not found”);

}

Stateful Session Bean Example

• TravelAgentBean

@Removepublic TicketDO bookFlight (CreditCardDO card, double price)

throws IncompleteConversationalState {

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

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);return ticket;} catch(Exception e) {

throw new EJBException(e);}

}

Stateful Session Bean Lifecycle

Does Not Exist

Method-Ready Passive

Stateful Session Bean Lifecycle

Does Not Exist

Method-Ready

Class.newInstance()injections

@PostConstruct

Stateful Session Bean Lifecycle

Does Not Exist

Method-Ready

@PreDestroy

Stateful Session Bean Lifecycle

Method-Ready Passive

@PrePassivate

Stateful Session Bean Lifecycle

Method-Ready Passive

@PostActivate

Stateful Session Bean Lifecycle

Method-Ready BusinessMethods

Stateful Session Bean Lifecycle

Does Not Exist

Method-Ready Passive

Timeout!

Stateful Session Bean Lifecycle

Does Not Exist

Method-Ready

instance throwssystem exception!

BusinessMethods

Stateful Session Beans and Extended Persistence Contexts

• Previous example used transaction-scoped Persistence Context– Objects become detached at end of every

method• Extended Persistence Context

– Loaded entities remain managed across method calls

– Automatically registered with a transaction• Only Stateful session beans can inject an

EXTENDED persistence context– Context is created and attached before

@PostConstruct– Context cleaned up when bean instance is

removed

Stateful Session Beans and Extended Persistence Contexts

import static javax.persistence.PersistentContextType.EXTENDED;

@Statefulpublic class TravelAgentBean implements TravelAgentRemote {

@PersistenceContext(unitName=“titan”, type=EXTENDED)private EntityManager entityManager;…public void updateAddress(Address addr) {

customer.setAddress(addr);}…

}

Session Beans

Deployment DescriptorStructure

The Deployment Descriptor

<?xml version="1.0"?><!DOCTYPE ejb-jar PUBLIC “-//Sun Microsystems,

Inc.//DTD EnterpriseJavaBeans 1.1//EN” “http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd”>

<ejb-jar> <enterprise-beans>

<session> <ejb-name>TravelAgentEJB</ejb-name> <home>com.relaxalot.TravelAgentHomeRemote</home> <remote>com.relaxalot.TravelAgentRemote</remote> <ejb-class>com.relaxalot.TravelAgentBean</ejb-class>

<session-type>Stateless</session-type></session>

</enterprise-beans></ejb-jar>

The Document Header

<?xml version="1.0” encoding=“UTF-8”?><!DOCTYPE ejb-jar PUBLIC “-//Sun Microsystems,

Inc.//DTD EnterpriseJavaBeans 1.1//EN” “http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd”>

The Descriptor’s Body

<ejb-jar><description>

Provide information about deployment descriptor (optional)

<display-name>Visual label used by deployment tools (optional)

<small-icon> and <large-icon>16x16 or 32x32 icons used by deployment tools

(optional)<enterprise-beans>

Describes one or more enterprise beans (one required)<ejb-client-jar>

Path of the client JAR (optional)

<assembly-descriptor>Defines how the enterprise beans are used in an

actual application (optional)</ejb-jar>

Enterprise Beans

<enterprise-beans><session> ...</session> Describe any number of session beans

<session> ...</session>

<entity></entity> Describe any number of entity beans

<entity> ...</entity>

</enterprise-beans>

Session Beans

<session><ejb-name> Name of component (one required) <home> Fully qualified class name of remote home interface (one required)

<remote> Fully qualified class name of remote interface (one required)

<ejb-class> Fully qualifed class name of bean class (one required)<session-type> Declares a session bean to be stateful or stateless (one required)

<transaction-type> Declares Bean or Container managed transactions (one required)

<security-role-ref> Declares security roles used by the EJB (zero or more)

<env-entry> Resource references (zero or more)

<ejb-ref> <resource-ref> </session>

Entity Beans<entity>

<ejb-name> Name of component (one required) <home> Fully qualified class name of remote home interface (one required)

<remote> Fully qualified class name of remote interface (one required)

<ejb-class> Fully qualifed class name of bean class (one required)<primkey-field> Primary key field (optional)

<prim-key-class> Primary key class (one required)

<persistence-type> Container or Bean (one required)<reentrant> Bean allows loopbacks: True or False (one required)

<cmp-field> Container managed persistence field (zero or more)<security-role-ref> Declares security roles used by the EJB (zero or more)

<env-entry> Resource references (zero or more)

<ejb-ref> <resource-ref> </entity>

Environment Entries

• Declaring<env-entry>

<env-entry-name>minCheckNumber</env-entry-name> <env-entry-type>java.lang.Integer</env-entry-type>

<env-entry-value>2000</env-entry-value></env-entry>

• Accessing InitialContext jndiContext = new InitialContext(); Integer minimumValue = (Integer)

jndiContext.lookup(“java:comp/env/minCheckNumber”);

References to Other Beans

• Declaring<ejb-ref>

<ejb-ref-name>ejb/RoomHomeRemote</ejb-ref-name> <ejb-ref-type>Entity</ejb-ref-type>

<home>com.relaxalot.RoomHomeRemote</home> <remote>com.relaxalot.RoomRemote</remote></ejb-ref>

• Accessing InitialContext jndiContext = new InitialContext(); Object ref =jndiContext.lookup(“java:comp/env/ejb/RoomHomeRemote”);

References to External Resources

• Declaring<resource-ref> <description>DataSource for RelaxInc

database</description><res-ref-name>jdbc/RelaxInc</res-ref-name> <res-type>javax.sql.DataSource</res-type>

<res-auth>Container</res-auth></resource-ref>

• Accessing InitialContext jndiContext = new InitialContext(); DataSource source = (DataSource)jndiContext.lookup(“java:comp/env/jdbc/RelaxInc”);

Describing Bean Assembly

<assembly-descriptor> <container-transaction>

Declares transaction attributes per each method (zero or more)<security-role>

Declares security roles used when accessing a bean (zero or more)<method-permission>

Declares which security roles are allowed to call one or more of the bean’s methods (zero or more)

</assembly-descriptor>

Session Beans

Topics to be Covered:• Purpose and Types of Session Beans• Stateless Session Beans• Stateful Session Beans• Session Bean Design• Deployment Descriptor Structure