Enterprise Java Beans

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Enterprise Java Beans

• Server Side Java Application Programming

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Overall structure
Database
Java Application
Middle Tier Server
Web Browser
File System
Mobile Phone
Legacy Application
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J2EE Server
J2EE Server
EJB Container Stateless Session Bean Stateful
Session Bean Entity Bean
Clients
Back end services
Web Container Servlet JSP Html/ Images
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Interacting with EJBs

• Normally servlets and JSPs will interact with
  EJBs
• However a client application can also directly
  interact with EJBs

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J2EE Services

• EJB container provides
• Transaction Management
• Security
• Remote Client Connectivity
• Life Cycle Management
• Database Connection Pooling

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Enterprise Java Beans

• Contain the business logic of the application
• Session Beans
• Stateless Session Beans
• Stateful Session Beans
• Entity Beans
• Container Managed Persistence
• Bean Managed Persistence (Ejb 3 has no BMP)

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Session vs Entity Beans
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Session and Entity Use Example
J2EE Server
EJB Container
Database
Entity Bean
Entity Bean
Session Bean
Web Container
Web Browser
Servlet
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Structure of a J2EE Application
J2EE Application
J2EE App DD
.ear file
Web Component
Enterpries Bean
Web Comp DD JSP file Servlet class GIF/jpeg
File HTML File
EJB DD EJB class Remote class Local class
.jar file
.war file
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Standard Deployment Descriptors

• Enterprise Archive (ear) file
• application.xml inside the META-INF directory
• Java Archive (jar) file
• ejb-jar.xml inside the META-INF directory
• Web Archive (war) file
• web.xml inside the WEB-INF directory

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Application Server

• Netbeans 6 uses the Glassfish V2 Application
  Server
• Others can be used if wanted
• To deploy a J2EE application on Glassfish V2 we
  need to add several vendor deployment descriptors
• sun-web.xml inside the WEB-INF directory
• sun-ejb-jar.xml inside the META-INF directory

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Enterprise Beans

• All enterprise beans need
• Bean Class
• Implementation of the bean
• Local Interface
• Allows Clients to Connect in the same Virtual
  Machine, very efficient
• Remote Interface
• Allows Clients to connect using RMI/ IIOP, used
  when client in different virtual machine.

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Session Beans

• Bean Class
• Implements the business method of the bean
• Local Interface
• Defines the business methods that a local client
  can call.
• Remote Interface
• Defines the business methods that a remote client
  can call.
• NOTE the business methods are implemented in the
  Bean Class

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Session Bean Class

• Implements the SessionBean Interface
• Must define
• One or more ejbCreate methods
• ejbRemove()
• ejbActivate()
• ejbPassivate()
• setSessionContext(SessionContext sc)
• In Ejb3 implemented via _at_Stateless of
  _at_Stateful annotation
• Can define additional business methods
• Must Implement any Local and Remote Interfaces

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Session Bean Class Business Methods

• Addition business methods can be defined in the
  Session Bean Class
• public double convertL(double dollars)
• return dollars 1.95
• public double convertR(double dollars)
• return dollars 1.95

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Session Bean Local Interface

• Local Interface defines any business methods that
  a local client may invoke
• These methods signatures must match exactly those
  business methods defined in the Session Bean
  Class
• public double convertL(double dollars)

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Session Bean Remote Interface

• Remote Interface defines any business methods
  that a remote client may invoke
• These methods signatures must match exactly those
  business methods defined in the Session Bean
  Class
• public double convertR(double dollars)

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Packaging the Session Bean

• The Session Bean is packaged into a jar file
  before deployment
• The Netbeans IDE packages the bean including any
  deployment descriptors
• ejb-jar.xml
• sun-ejb-jar.xml

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Accessing and using the Session Bean (from a
Servlet)

• Declare the Session Bean using the _at_EJB
  annotation
• _at_EJB
• private sbConvLocal sbConvBean
• Use the Session Bean in the servlet code
• sbConvBean.convL(100)

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Stateful Session Bean Lifecycle
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Stateless Session Bean Lifecycle
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Summary

• Main points to remember
• J2EE Application server
• EJB container
• Entity and Session Beans
• Session Bean details
• Bean Class
• Home Interface
• Remote Interface