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J2EE

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The JavaTM Platform

Most of you know there are three flavors of Java - Micro Edition,

Standard Edition, and Enterprise Edition. These three flavors of Java represent

three distinct target market segments each of which has unique issues and

requirements that need to be addressed somewhat differently.

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What is J2EE? Sun's J2EE architecture is multi tiered architecture and it

eliminates all the problems of two-tier architecture. It alsoeliminates the need of writing thin-client multithreadapplications, which were earlier used to write distributedtransactional applications for the enterprise.

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What is J2EE?

Thin-client multi tiered applications are very fast, secure andreliable. But writing the thin-client multi tiered applicationsare not easy and it involves many lines of complicated codeto handle transaction and state management,multithreading, resource pooling and other complex low-level details.

In the Java TM 2 Platform, Enterprise Edition (J2EE tm), low-level details are separated from the business logic. Now thedevelopers will more concentrate on the business logic

rather than the low-level details. Low-level details aremanaged by the application container of the applicationserver.

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Need for Enterprise programming

A well designed enterprise application should meet thefollowing goals

Robustness

Performance Object Oriented design Principles

Avoid Complexity

Maintainable and Extensible

Easy to Test Promote reuse

Support for the multiple client types

Portability

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Advantages of J2EE

Specifically there are two major paths to developenterprise applications first is .NET platformsuite by Microsoft and second J2EE by Sun. There

are lot of other companies also like BEA, IBM,Oracle, etc. Having all these choices Java has agreat acceptance because of followingadvantages

Platform Independence

Managed Objects

Reusability

Modularity

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Platform Independence

Enterprise applications comprises of wide

variety of information which has to spread

across many different type of platforms.

Hence, it is essential to have a programming

language that is capable of running across the

different platforms and that is Java.

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Managed Objects

The platform independent J2EE provides a

managed environment for component.

J2EE applications are container-centric.

Another important property of the J2EE

applications is the ease by which it can

modify and control the behavior of

applications without changing the codes.

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Reusability

In the programming field, the code reuse is the

most important and desired feature. This can

be done by following ways

To segregate an applications requirements

into individual components.

To use object oriented technology to

encapsulate shared functionality.

Java uses both the ways.

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Modularity

When we develop a complete server-side

application, the program get large and

complex very quickly. It is always best to

break down the application into variousmodules that are individually responsible for

a specific task. This also makes the

application much easier to maintain andunderstand.

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Enterprise Architecture Types

A software application composition can be broken

down into three logical layers

User Interface Presentation Layer

Processing Business Rule Layer

Reading and Writing Data Data Access Layer

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Single Tier Architecture

Some applications aredeveloped to run on a single

computer.In these type of applications all

functionalities are embeddedwith in the same layer, suchas user interface, processing,data manipulation, etc.

Such type of architecture is

called single

tier systems.

User Interface

Processing

Reading/Writing

Data

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Two Tier Architecture

User

Interface

On

Clients

Business Rule

Data Access

On

Server

Before the invention of

PCs, applications were

developed to run on

mainframe based client-server environment which

used a thin client and

thick server. Because

application was

predominantly run on

server side.

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Layers of Two Tier

Architecture

The approach of these applications are centralizedin which multiple users are allowed to work

simultaneously. Clients provide only userinterface and rest of all the processes are run onserver side. All the services and data accessprovided by server is shared by all the usersworking on the application.

User Interface Layer

Business Rule, Data Access Layer

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Three Tier Architecture

In this type application logic is divided intothree layers

1. Presentation Layer User Interface Tier

2. Business Logic LayerBusiness Rule Tier

3. Data Layer

Data-Store Tier

Clients Application Server Database Server

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Layers of Three Tier Architecture

Data-Store Tier This tier is concerned with the

storage and retrieval of data from databases.

User Interface Layer

Business Rule Layer

Data Access Layer

User-Interface Tier

This

tier handles the user

interface logic. This is

normally on the client side. Business Rule Tier This

tier handles all of the

business rules logic andvalidates user input from

user interface tier.

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Advantages of Three Tier Architecture

Moving business rule components to anapplication server can boost performance.

Multiple application servers can take

advantage of load balancing and improvesystem fault tolerance.

Changes to business rule can migrate to asmall number of application servers insteadof a large number of workstations.

This also provides better code encapsulationallowing different people or even companies

to implement each tier.

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Multi Tier Architecture

Presentation LayerUser Interface Tier

Presentation Logic Layer

User InterfaceOriented Business Logic Tier

Business Logic LayerBusiness Rule Tier

Data Layer

Data-Store Tier

UIOrientedBusinessRule

Application Server Database ServerBusiness RuleClients

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Layers of Multi Tier Architecture

1.This handles the UI logic, whichincludes the actual presentationof screens and collectinformation.

2.This layer handles business rule

logic that supports the UI. Forexample, validation of user input.3.This is responsible for data

manipulation and integration. Itcan combine data from SQL

databases with flat files or evenInternet resources.4.This layer handles the storage and

retrieval of data from databases,files, and other data sources.

1 - User Interface Layer

2-UI-Business Rule Layer

3 - Business Rule Layer

4Data Access Layer

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Advantages of Multi Tier Architecture

The central idea in multi-tier architecture is to keep theservices physically close to data they work with.Multi-tier architecture lets us put UI Oriented business

rule components which are an excellent candidates for JavaBeans which let us to create reasonable, platform independent components.

Data oriented business rule components are an excellentcandidates for Enterprise Java Beans (EJB) which providesthe facility of distributed programming.

Multi tier is a component based architecture. Thereforebusiness logic services that support the UI can remainphysically close to the client. Remaining applicationservices can scale as additional resources become available.

The multi tier architecture is flexible about the placementand the presence of application servers.

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J2EE Architecture

The J2EE Architecture allows the programmers to divide their workinto two major categories

Presentation Logic

Presentation Logic consists of all the program (JSP and Servlets),

images and html files that are used to interact with the client.These files are archived into .war file. These files are installed onthe web server and these interact with the users.

Business Logic

These are EJB applications which implement the business logic of

the system and are archived into .jar file. Business logic runs onthe application server.

These two types of archives are bundled into complete J2EEapplications, and delivered as Enterprise Archive (EAR) file.

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A typical J2EE Environment

EIS-TierClient - Tier Middle-Tier

Enterprise

InformationSystem

(RDBMS,

ERP,

Legacy

Applications)

Client

Client

Client

EJB Container

JNDI,

JMS,

JavaMail

Enterprise

bean

Enterprise

bean

Enterprise

bean

Client

Web

Container

(Servlets,

JSP Pages,

HTML, XML)

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J2EE Components

The J2EE platform is a distributed applicationserver environment, i.e. Java environmentcomprises of following components

A runtime infrastructure for managing andhosting applications. All runtime applicationsare located in this server.

A set of Java APIs to build applications. These

Java APIs describe the programming model forJ2EE applications. For example, Java ServletTechnology, EJB Technology, JSP technology, etc.

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J2EE Containers

Containers are the interface between a

component and the low-level platform-

specific functionality that supports the

component.

Before a Web, enterprise bean, or application

client component can be executed, it must be

assembled into a J2EE application anddeployed into its container.

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Container Types

The deployment process installs J2EE application components in

the J2EE containers illustrated in Figure

http://java.sun.com/j2ee/1.3/docs/tutorial/doc/Overview4.htmlhttp://java.sun.com/j2ee/1.3/docs/tutorial/doc/Overview4.html

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Container Types

J2EE server - The runtime portion of a J2EEproduct. A J2EE server provides EJB and Webcontainers.

Enterprise JavaBeans (EJB) container - Managesthe execution of enterprise beans for J2EEapplications. Enterprise beans and their containerrun on the J2EE server.

Web container - Manages the execution of JSPpage and Servlet components for J2EEapplications. Web components and their containerrun on the J2EE server.

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Container Types

Application client container - Manages the

execution of application client components.

Application clients and their container run onthe client.

Applet container - Manages the execution of

applets. Consists of a Web browser and JavaPlug-in running on the client together.

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J2EE TechnologiesJ2EE Architecture consists of following

technologies:

Java Database Connectivity (JDBC)

Java Naming and Directory Interface (JNDI) Enterprise Java Beans (EJB)

Java Server Pages (JSP)

Java Servlets Remote Method Invocation (RMI)

Java IDL/CORBA