Chapter 8b: Business Logic Tier: Session EJB

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Chapter 8bBusiness Logic TierSession EJB
Reference Eclipse WTP
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Objectives

• Enterprise Java Beans
• Distributed Application Using EJBs
• Types of EJBs
• Developing Session EJBs
• Writing EJB Clients

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What are EJBs

• Enterprise JavaBeans (EJBs) server-side software
  components that conform to the J2EE architecture
  for development and deployment of distributed
  systems
• J2EE-compliant application servers must provide a
  run-time environment for the EJBs an EJB
  container

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Distributed Application Using EJBs
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Types of EJBs

• Session beans
• can perform any kind of processing
• models business processes (coarse-grained
  components)
• Entity beans
• represent persistent data
• models fine-grained data objects
• Message-driven beans (MDB)
• used with messaging software

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Major Components of an EJB

• Bean class
• Implements the business methods
• Home interface
• Defines the methods that allows clients to
  create, find and remove EJB objects
• Remote interface
• Defines the business methods callable by the a
  remote client

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MVC Architecture
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EJB Containers and Services

• The role of the EJB container is to provide the
  following
• The distribution infrastructure and a naming
  service to help client code locate and access
  EJBs.
• The ability to place EJBs in a scalable
  architecture
• Support for concurrent access
• Resource management, including connection pooling
• Security services in addition to the secure
  environment that can be configured for
  applications loaded into the application server
• Transaction managers that interact with JDBC
  drivers and resource adapters

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J2EE Enterprise Application Packaging and
Deployment

• EJBs are always packaged in J2EE enterprise
  applications
• Files that compose EJBs are packaged in jar files
• An EJB jar must contain a deployment descriptor
  file (ejb-jar.xml)

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J2EE Packaging into Archive Files
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Session EJBs

• Session EJBs can do general purpose processing
• Associated with the client that calls them
• There are two types of session EJBs
• stateful
• stateless
• EJB Design Pattern Session Façade (p.327)
• E.g., LeagueFacade EJB wraps the IceHockeyFacade
  object

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Stateless Session EJBs

• Can be shared among clients
• Methods defined in the javax.ejb.SessionBean
  interface are call-back methods (e.g.,
  ejbCreate()) that control the lifecycle of the
  bean, that are called by the container

public abstract class LeagueFacadeBean
implements LeagueFacade, javax.ejb.SessionBean
/ _at_ejb.create-method view-type"remote"
/ public void ejbCreate() leagueFacade
IceHockeyFacade.getLeagueFacade()
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Iteration 2 Developing Session EJBs

• Reference Pages 325 -355
• General Steps
• Create an EAR and EJB projects
• Create a Stateless Session Bean
• Note Home and Remote Interfaces generated by
  XDoclet
• Add business methods to Bean class
• Note can be automatic if interface specified in
  Wizard
• Add XDoclet annotation to set the view-type (e.g.
  both)
• Business methods added to Local and Remote
  Interface
• Build a Web client
• Run the Web client
• Deploy and test the Session Bean

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Developing Session EJBs Using Eclipse WTP

• New XDoclet Enterprise JavaBean

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EJB Component Class DiagramReference page 329

• Assembled into LeaguePlanetEJB.jar
• In the com.leagueplanet.ejb package, only
  LeagueFacadeBean code typically changed by
  developer the other class/interfaces
  auto-created by XDoclet.

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Sample EJB Bean Class

• Implement findLeague() method by calling
  findLeague() method of the IceHockeyFacade
  (service layer).

import com.leagueplanet.services.LeagueFacade p
ublic abstract class LeagueFacadeBean
implements LeagueFacade, javax.ejb.SessionBean
private LeagueFacade leagueFacade /
_at_ejb.interface-method view-type"both" / public
League findLeague(long id) return
leagueFacade.findLeague(id)
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Stateful Session EJBs

• Stateful session EJBs retain conversational state
  between method calls and are used by only one
  client
• Not emphasized in this course.
• Conversational state information that must be
  retained as long as the client is actively
  interacting with the application
• Transactional state data that must be
  permanently recorded when the client activity
  ends
• Note not covered in this course.

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Sample EJB Remote Home Interface

• Generated by XDoclet in LeaguePlanetEJBClient
  project

package com.leagueplanet.ejb / Home
interface for LeagueFacade. _at_wtp generated
/ public interface LeagueFacadeHome extends
javax.ejb.EJBHome public static final String
COMP_NAME "javacomp/env/ejb/LeagueFacade"
public static final String JNDI_NAME"LeagueFacade
" public com.leagueplanet.ejb.LeagueFacade
create() throws javax.ejb.CreateException,ja
va.rmi.RemoteException
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Sample EJB Remote Interface

• Generated by XDoclet in LeaguePlanetEJBClient
  project

package com.leagueplanet.ejb / Remote
interface for LeagueFacade. _at_wtp generated
/ public interface LeagueFacade extends
javax.ejb.EJBObject public
com.leagueplanet.model.League findLeague( long id
) throws java.rmi.RemoteException
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EJB Clients

• The EJB 2.0 specification adds interfaces to all
  entity and session beans specifically for use by
  co-located clients (i.e., located in the same
  JVM)
• Local interfaces added to EJB 2.0
• There are four interfaces (2 remote and 2 local)
  that you can define for a session or entity bean
• Interfaces automatically generated by XDoclet
  based on the view-type

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Writing EJB Clients

• Reference Pages 349 - 352
• The client calls getHome() method generated by
  XDoclet.
• getHome() performs a lookup to the JNDI namespace
  using the JNDI_NAME (e.g., LeagueFacade)
• When the client has the EJB home, it uses a
  create() method to get a handle to the remote
  interface
• When the client has the EJB remote object, it
  calls the business methods (e.g., findLeague())

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Sample EJB Client

• In schedule.jsp (EJB client), we use the EJB
  Session Bean (e.g., LeagueFacade) to call
  findLeague() method.

lt_at_page import"com.leagueplanet.ejb.LeagueFacad
e"gt lt_at_page import"com.leagueplanet.ejb.LeagueFa
cadeUtil"gt lt LeagueFacade leagueFacade
LeagueFacadeUtil.getHome().create() League
league leagueFacade.findLeague(1) Iterator
schedules league.getSchedules().iterator() gt
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Next Steps

• Chapter 8 Tutorial
• Iteration 2. Session EJBs
• LeaguePlanetEJB LeagueFacadeBean
• LeaguePlanetEJBClient
• LeaguePlanetWeb schedule.jsp
• Assignment 3
• XXYYSurveyEJB XXYYSurveyFacade
• XXYYSurveyEJBClient