1' JavaJ2EERMI overviewKoteswara Kommineni, Uday Rivella

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Team Presentations Outline

• 1. Java/J2EE/RMI overview-Koteswara Kommineni,
  Uday Rivella
• 2. EJB Overview
• EJB Concepts -Sarah Lee
• EJB Component Life Cycle, code walkthrough -
  Tracey Wilburn
• 3. Development Methodology-Manjeera Madduri, Xing
  Ruan
• 4. CMMI-related Challenges with EJB Component
  Development - Kavita Kolli
• 5. Summary/Comparison - Shekhar Vemuri

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Topic 2 Enterprise Java Bean Technology Technical
Concepts Sarah B. Lee April 16, 2003
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Java Review

• Java 2 Platform, Enterprise Edition (J2EE)
• component-based, platform independent
  architecture
• Java Naming Directory Interface (JNDI)
• provides unified interface to directory naming
  services
• Remote Method Invocation (RMI)
• provides a means of communicating between Java
  apps on separate machines

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Enterprise Java Beans Model

• Provides a framework for component based
  distributed computing
• specifies how distributed components should work
  within the Java environment
• Makes thin-client, multi-tiered apps easier to
  write
• separates low-level details from business logic

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What is an Enterprise Java Bean?

• Body of code written to implement modules of
  business logic
• Standard extension to Java
• available in javax.ejb package
• latest version http//www.javasoft.com/products/e
  jb
• must be explicitly installed to write code
  against EJB interfaces

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EJB Component Model
EJB Server
Client
EJB Container
client request
EJB
The container manages the enterprise beans at
runtime
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EJB Application Server
EJB Server
Client
EJB Container
client request

• Required when using EJB
• Contains EJB containers which
  manage EJB objects
• Primary goals
• Improve performance
• Simplify development
• Most important feature efficient resource
  management

EJB

• iPlanet/Netscape (AOL/Netscape/Sun)
• NetDynamics (Sun)
• Weblogic (BEA)
• WebSphere (IBM)

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EJB Containers
EJB Server
Client

• Set of classes that manage an enterprise beans
• Persistence
• bean state maintained in permanent data
  store
• Start, enrollment, commitment, and rollback of
  transactions
• Security
• Insulate the EJBs from direct access from client
  applications
• whenever a bean is requested, created, or
  deleted, the container manages the whole process

EJB Container
client request
Persistence Mgmt Transaction Mgmt Security Mgmt
EJB
Containers live and operate inside EJB Servers
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EJB Interfaces
Each enterprise bean exposes 2 interfaces via the
container to the client

• Home Interface
• Defines the methods that allow clients to create,
  find, and remove EJB objects
• Creates instances of the remote interface for an
  enterprise bean
• Remote Interface
• Used by client to invoke operations on the bean
• Describes what the bean does

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Types of EJBs

• Session bean
• a transient object
• lifespan is limited to that of the client
• works with one client
• business logic

• Entity bean
• a persistent object
• lifespan is as long as the database
• multiple clients simultaneously
• represents data in a database

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Session Beans

• Created by client
• exist only for duration of single client/server
  session
• Performs operations on behalf of client
• ex performing calculations
• Normally not recoverable after system crash

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Session Beans

• Two types
• Stateful
• keeps information across http requests
• Stateless
• information is not kept

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Entity Beans

• Persistent
• state is maintained in permanent data store
• exists as long as the corresponding data exists
  in the database
• Can be recovered after system crash
• Each bean identified by primary key
• unique identifier that enables client to locate
  particular entity bean
• ex customer entity bean might be identified by
  customer number

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Entity Beans

• Two Types of Persistence
• bean-managed
• container-managed

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Entity Beans Bean-Managed Persistence

• Entity bean code contains the calls that access
  the database
• Programmer is responsible for coding the insert
  statement and any other necessary SQL

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Entity Beans Container-Managed Persistence

• Container automatically generates necessary
  database access calls
• ex when client creates entity bean, container
  generates SQL Insert
• Programmer code contains no SQL calls
• Entity bean is independent of any particular
  database

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EJB Server
Entity Home
Entity Bean
Database
JNDI
Entity Remote
Container
RMI
Browser
Client App
Session Home
JNDI
Session Bean
RMI
Session Remote
Container

• Client application
• Interacts with EJBs through home and remote
  interfaces
• EJB Server
• Handles low-level details including database I/O
• Container
• Provides interface between EJB and low-level
  platform specific functionality

• Home Interface
• Describes how client creates, finds, removes EJB
  from container
• Located by client using JNDI
• Remote Interface
• Describes beans methods (what it does)
• Client calls methods defined in remote interface
  to invoke business logic
• Invoked using RMI

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Typical Enterprise JavaBeans Network Security
Topology
Applets
Web server
EJB Server
Internet
Browsers
Web server
EJB Server
Enterprise information
Applications
DMZ
Firewall 2
Firewall 1
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Benefits of Using EJB

• Productivity
• Industry Support
• Architectural Independence
• Server-Side Write Once, Run Anywhere?

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Topic 2 Enterprise Java Bean Technology Code
Walkthrough Tracey Wilburn April 16, 2003
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Coded Example of EJB Object

• Hello World
• stateless session bean
• EJB Environment
• interaction between code

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Client Code

• Purpose
• Locate an object
• Create a new instance of an object
• Obtain business method operation

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Locate an Object

• JNDI (Java Naming and Directory Interface)
• Four steps to locate an object
• Initialize JNDI properties
• Initialize Naming Context
• Lookup the Object
• Narrow the Object

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Deployment Identifier

• tells the container the name to use for
  registering the beans home interface in the JNDI
• must be unique

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Client Code

• import javax.rmi.
• import javax.naming.
• import java.util.
• public class HelloWorld
• public static void main( String args)
• try
• Properties p new Properties()
• //The JNDI properties you set depend
• //on which server you are using.
• //These properties are for the Remote Server.
• p.put("java.naming.factory.initial",
  "org.openejb.client.RemoteInitialContextFactory")
  
• p.put("java.naming.provider.url",
  "127.0.0.14201")
• p.put("java.naming.security.principal",
  "myuser")
• p.put("java.naming.security.credentials",
  "mypass")

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Client Code (Cont.)

• //Use the HelloHome to create a HelloObject
• HelloHome ejbObject ejbHome.create()
• //The part we've all been waiting for...
• String message ejbObject.sayHello()
• //A drum roll please.
• System.out.println( message )
• catch (Exception e)
• e.printStackTrace()

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Developing an EJB Object

• Home Interface
• Remote Interface
• Enterprise Bean Implementation

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EJB Specifications

• Home Interface
• throws CreateException
• throws RemoteException
• create( )

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Home Interface Code

• import java.rmi.
• import javax.ejb.
• import java.util.
• public interface HelloHome extends EJBHome
• public HelloObject create() throws
  RemoteException, CreateException

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EJB Specification

• Remote Interface
• throws RemoteException
• Methods defined must match methods in EJB class
• Signature of methods must be identical to methods
  in EJB class

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Remote Interface Code

• import java.rmi.
• import javax.ejb.
• import java.util.
• public interface HelloObject extends EJBObject
• public String sayHello() throws
  RemoteException

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EJB Specifications

• Enterprise Bean Implementation
• void ejbPassivate()
• void ejbActivate()
• void ejbCreate()
• void ejbRemove()
• void setSessionContext()

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EJB Specification

• Enterprise Bean Implementation
• Implement Business Method
• EJB class must be defined as public

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Enterprise Bean Implementation Code

• import java.rmi.RemoteException
• import javax.ejb.
• public class HelloBean implements SessionBean
• private SessionContext sessionContext
• public void ejbCreate()
• public void ejbRemove()
• public void ejbActivate()
• public void ejbPassivate()
• public void setSessionContext(SessionContext
  sessionContext)
• this.sessionContext sessionContext
• public String sayHello() throws
  java.rmi.RemoteException
• return "Hello World!!!!!"

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EJB Example Code
EJB Server
EJB Container
Home Interface
Lookup
Client
Remote Interface
EJB
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EJB Example Code
EJB Server
Reference of Home Interface
EJB Container
Home Interface
Client
Remote Interface
EJB
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EJB Example Code
EJB Server
EJB Container
Home Interface
Client
create( )
ejbCreate()
Remote Interface
EJB
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EJB Example Code
EJB Server
EJB Container
Home Interface
Client
Remote Interface
Reference of Remote Interface
EJB
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EJB Example Code
EJB Server
EJB Container
Home Interface
Client
Locate business method
Remote Interface
EJB
Business method invoked
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EJB Example Code
EJB Server
EJB Container
Home Interface
Client
Remote Interface
EJB
Returns business method