EJB Overview

Celsina Bignolibignolic@smccd.net

Distributed Business Applications

Server Server

DB

ClientClient ClientClient

DB

Server DBDB

Distributed Systems – Issues

• Remote method invocation

• Load balancing

• Transparent fail-over

• Back-end integration

• Transactions

• Clustering

• Dynamic redeployment

• Clean shutdown

Distributed Systems – Issues(2)

• Logging an auditing

• System management

• Threading

• Message-oriented middleware

• Object life cycle

• Resource pooling

• Security

• Caching

Middleware

• Each issue correspond to a service that needs to be addressed in serious server-side computing (middleware)

• A company can build its own middleware– Complicated to build and maintain– Requires expert-level knowledge– Completely orthogonal to most companies’ core

business• A company can buy an application server

– They implement the middleware layer– Allow developer to focus on the code specific to

the vertical industry

Component Architecture

• Agreement or set of interfaces between application servers and components

• Allows any component to run within any application server without changing code or even recompiling it

Enterprise JavaBeans (EJB)

• Standard for building server-side components in Java

• Defines a contract between components and applications servers, agreed upon by the industry

• Focus on vertical, rapid business development rather than middleware development

• Designed to support portability, scalability and reusability across any vendor’s middleware services

EJB as Business Tier

• Enterprise Beans are server-side components– Perform complex computations to code business logic– Access databases– Access other systems– Must run in a fault-tolerant, transactional, multi-user,

secure environment

• Enterprise Beans are NOT presentation components

• Sit BEHIND the presentation layer (and do the hard work)

EJB Ecosystem

Supply Tools

Construct

Enterprise Beans

Tool Provider(EclipseJDeveloperNetBeans

Sun’s Java Studio)

Build Application

Bean Provider

Application Assembler

Supply

EJB Container

Deploy System

Deployer SystemAdministrator

EJB Container/Server Provider(BEA WebLogic

jBoss, WebSphere, … )

J2EE Architecture

Browser

ApplicationClient

Client

Servlet JSP Page

Web Container

EnterpriseBean

EnterpriseBean

EJB Container

J2EE Server

Database

J2EE Technologies

• Enterprise JavaBeans (EJB)• Java API for XML RPC (JAX-RPC)• Java Remote Method Invocation (RMI-IIOP)• Java Naming and Directory Service (JNDI)• Java Database Connectivity (JDBC)• Java Transaction Service (JTS)

J2EE Technologies

• Java Messaging System (JMS)• Java Servlets• JavaServer Pages (JSP)• Java IDL (CORBA)• JavaMail• Java API for XML Parsing (JASP)• Java Authentication and Authorization

Service (JAAS)