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IBM Software Group

© 2007 IBM Corporation

J2EE Web Component Introduction

4.1.0.3

2

After completing this unit, you should be able to: Understand the stages in the development of Web

applications Describe the model-view-controller (MVC) design pattern Understand the importance of MVC in J2EE applications Describe the web components and containers provided by a

J2EE platform Describe the web architecture of J2EE

After completing this unit, you should be able to: Understand the stages in the development of Web

applications Describe the model-view-controller (MVC) design pattern Understand the importance of MVC in J2EE applications Describe the web components and containers provided by a

J2EE platform Describe the web architecture of J2EE

Unit objectives

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Web Browser

Web Server

File System

HTTP Request

HTTP Response

Client Network Server

Web Application Evolution – Static

Organizations want to make their information available to as many people in the world as possible

This can be achieved by using the Web, delivering the information as static HTML pages

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Web Server

File System

HTTP Request

HTTP Response

Client Network Server

Web Application Evolution – Applets

With static HTML, users see passive page presentations which are always the same

Presentation can be improved with Java applets or other client-side programs

Web Browser with JVM

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Netw

ork

Web Browser

Web Server

File System

HTTP RequestClient

Web Server Plug-in

Server

Web Container

Web Application Evolution – Servlets

Applets cannot access data on back-end systems A Web container can provide server-side components (such as

servlets) to generate dynamic content

Requests for dynamic

resources

Requests for static

resourcesHTTP Response

Dynamicresponse

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JavaServer Page

JavaBean

RequestDispatcher

Request

Response

Web Containerservice(req,res)

methods()

methods()

forward(req,res)

service(req,res)

Web Application Evolution – JSP Pages

Servlets give poor separation between business logic and presentation logic

Use JavaServer Pages and JavaBeans to improve separation

Servlet

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Web Application Evolution – Scalability

Business requirements often involve high availability Improved performance may be required as business grows Both these requirements can be achieved through scaling

Servers can provide redundancy in the systemBy sharing the load between servers, performance can be

enhanced

WebBrowser

HTTPServer

WebContainer

WebContainer

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The Model-View-Controller Pattern Model-View-Controller (MVC) is a design pattern

Very widely used and regarded as a core concept in J2EE development

Various practical benefits (covered in more detail later) Promotes code reuse Reduces development time

The model Represents the underlying data and business logic in one place Contains no information about the user interface

The view The user interface – things the user can see and respond to Represent a window into the model – there can be many of these

The controller Connects the model and the view Used to communicate between the model and view

A fourth layer – persistence – is often added to the pattern

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J2EE Server

View

Controller

Database

Model

Persistence

MVC – Application to J2EE

WebBrowser

TransferServlet Transfer

JavaBean

TransferResult

JavaBean

HTMLDoc

HTMLDoc

5

2

3

4

6

7

1

BalanceJSP

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MVC – Benefits Promotes code reuse

The purpose of the model is to provide business logic and data access in one place

This logic can be reused in many applications at the same time without the need for any extra coding

Reduces development timeThe model, view, and controller are developed in parallel

More maintainableThe view can be changed without affecting the model

A Web page view can be changed to display a chart instead of a table with no change to the model

The model can be changed without affecting the view For example, the way in which an insurance premium is calculated

changes, but the interface to the business method remains the same

Data can be moved without affecting the view or model The layering concept allows for more flexibility

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J2EE Introduction The Java 2 Platform Enterprise Edition (J2EE) Specification

consists of:The J2EE Platform

A standard platform of containers, services and communications

The J2EE Compatibility Test Suite To verify that a J2EE platform product complies with the standard WebSphere Application Server 6.1 is J2EE 1.4 compatible

The J2EE Reference Implementation For prototyping J2EE applications and for providing an operational

definition of the J2EE platform

The J2EE Blueprints Best practices for developing multitier, thin-client applications

J2EE is developed using the Java Community ProcessCollaboration between major enterprise software vendorsIBM actively contributes to the J2EE development process

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J2EE Components J2EE defines different types of components which must be

supported by any J2EE productThis course will only cover Web components

Servlets and JavaServer Pages These provide the controller and view functionality in J2EE

Component deployment can be managed using deployment descriptors (except applets)

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J2EE Containers J2EE defines different types of container.

Containers manage the components they contain.This course will only cover Web component container

Provided by a J2EE application server

J2EE components never interact with other J2EE components directlyThey depend on the run-time support of containersInteraction takes place using services provided by

containers

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J2EE Architecture

RMI-IIOP

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EnterpriseInformationSystemsTier

J2EE Multitier Model

RelationalDatabases

Middle TierClient Tier

EnterpriseResourcePlanningSystems

LegacyApplicationsWeb

Container(Servlets,

JSPs,HTML)

WebClient

WebClient

Firewall

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J2EE Benefits Standards

A wide range of standard services, components, clients, and tools are supported

Applications are portable across J2EE platforms Distribution

Provides scalability for performance and availability Common services

Most commonly required services are provided by J2EE servers

Component modelGood separation of development responsibilitiesGood reuse of code and opportunities to share logic

between applications Interoperability

Integration with other systems using standard protocols

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Checkpoint

1. What role does a servlet play in a MVC application.2. What role does a JSP play in a MVC application.

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Checkpoint solutions

1. Servlets act as the controller in a MVC applicationa) Do not generate HTMLb) Convert the incoming HTTP information to Java objectsc) Interact with the business modeld) Forward to JSPs to render the View

2. JSP act as the Viewa) Do not contain business logicb) Simply display information

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Having completed this unit, you should be able to: Understand the stages in the development of Web

applications Describe the model-view-controller (MVC) design pattern Understand the importance of MVC in J2EE applications Describe the web components and container provided by a

J2EE platform Describe the web architecture of J2EE

Having completed this unit, you should be able to: Understand the stages in the development of Web

applications Describe the model-view-controller (MVC) design pattern Understand the importance of MVC in J2EE applications Describe the web components and container provided by a

J2EE platform Describe the web architecture of J2EE

Unit summary