Module 5 Session Beans. Topics to be Covered: Purpose and Types of Session Beans Stateless Session Beans Stateful Session Beans Session Bean Design Deployment.

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;

}


• 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 {}


• 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;

}}


• 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;

}}


• 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


• 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


• 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”;



@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);}

}



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()));}

}


• 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;

}



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


• 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>

http://java.sun.com/xml/ns/javaee

http://www.w3.org/2001/XMLSchema-instance

http://java.sun.com/xml/ns/javaee/ejb-jar_3_0.xsd

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


Does Not Exist

Method-ReadyPool

Class.newInstance()injections

@PostConstruct


Does Not Exist

Method-ReadyPool

@PreDestroy


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;

}


• Application Exception: IncompleteConversationalState

package edu.weber.travelagent;

public class IncompleteConversationalState extends java.lang.Exception {

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

}


• Domain Object: TicketDO

package edu.weber.travelagent;

public class TicketDO implements java.io.Serializable {

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

}


• 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


• 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;


• 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;

}


• TravelAgentBean

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

}


• 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”);

}


• 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


Does Not Exist

Method-Ready

Class.newInstance()injections

@PostConstruct


Does Not Exist

Method-Ready

@PreDestroy



@PrePassivate



@PostActivate


Method-Ready BusinessMethods


Does Not Exist


Timeout!


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

Module 5 Session Beans. Topics to be Covered: Purpose and Types of Session Beans Stateless Session Beans Stateful Session Beans Session Bean Design Deployment.

Documents

types of session beans

session beans purpose

reuse session beans

invalidated slide

beans specific

bean instance

persistent slide

video slide