JAVA Web Application Development

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Web Design & Development CS506

Lesson 25

Web Application Development

Introduction

Because of the wide spread use of internet, web based applications are becoming vital part of IT

infrastructure of large organizations. For example web based employee performance management systems

are used by organizations for weekly or monthly reviews of employees. On the other hand online course

registration and examination systems can allow students to study while staying at their homes.

Web Applications

In general a web application is a piece of code running at the server which facilitates a remote user

connected to web server through HTTP protocol. HTTP protocol follows stateless Request-Response

communication model. Client (usually a web-browser) sends

Figure 1: A typical web application

A web server is software which provides users, access to the services that are present on the internet. These

servers can provide support for many protocols used over internet or intranet like HTTP, FTP, telnet etc

HTTP Basics

A protocol defines the method and way of communication between two parties. For example when we talk

to our teacher we use a certain way which is different from the way that we adopt with our fiends or

parents. Similarly there are many different protocols used by computers to communicate with each other

depending on applications.

Figure 2: HTTP communication model

-HTTP is as request-response oriented protocol.

-It is a stateless protocol since there is no built-in state management between successive requests. We

will discuss state later.

Parts of an HTTP request

-Request Method: It tells the server the type of action that a client wants to perform

-URI: Uniform Resource Indictor specifies the address of required document or resource

-Header Fields: Optional headers can be used by client to tell server extra

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Figure 3: HTTP request example

-Body: Contains data sent by client to the server

-Other request headers like FROM (email of the person responsible for request) and VIA (used by

gateways and proxies to show intermediate sites the request passes) can also be used.

Request Parameters

Request can also contain addition information in form of request parameters

1. In URL as query string e.g. http://www.gmail.com/register?name=ali&state=punjab

2. As part of request body (see Figure 3)

Parts of HTTP response

Result Code: A numeric status code and its description. -Header Fields: Servers

use these fields to tell client about server information like configurations and

software etc. -Body: Data sent by server as part of response that is finally seen

by the user.

Figure 4: HTTP response example

HTTP Response Codes

An HTTP Response code tell the client about the state of the response i.e. whether it's a valid

response or some error has occurred etc. HTTP Response codes fall into five general categories

· 100-199

Codes in the 100s are informational, indicating that the client should respond with some

other action.

100: Continue with partial request.

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200-299

Values in the 200s signify that the request was successful.

200: Means every thing is fine.

300-399

Values in the 300s are used for files that have moved and usually include a Location header

indicating the new address.

300: Document requested can be found several places; they'll be listed in the returned

document.

400-499

Values in the 400s indicate an error by the client.

404: Indicates that the requested resource is not available.

401: Indicates that the request requires HTTP authentication.

403: Indicates that access to the requested resource has been denied.

500-599

Codes in the 500s signify an error by the server.

503: Indicates that the HTTP server is temporarily overloaded and unable to handle the

request.

404: indicates that the

requested resource is

not available

401: Indicates that

request requires HTTP

authentication

Server Side Programming

Web server pages can be either

static pages or dynamic pages.

A static web page is a simple

HTML (Hyper Text Transfer

Language) file. When a client

requests an HTML page the

server simple sends back response

with the required page.

Figure

Static

web

page

request

and

response

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An example of static web page is given

below While in case of dynamic web

pages server executes an application

which generates HTML web pages

according to specific requests coming

from client. These dynamically generated

web pages are sent back to client with the

response.

Figure 6: Dynamic web page request and response

Why build Pages Dynamically?

We need to create dynamic web

pages when the content of site

changes frequently and client

specific response is required.

Some of the scenarios are listed

below

-The web page is based on

data submitted by the

user. e.g. results page

from search engines and

order confirmation pages

at on line stores. ]

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The Web page is derived from data that changes frequently. e.g. a weather report or news headlines page.

The Web page uses information from databases or other server-side resources.

e.g. an e-commerce site could use a servlet to build a Web page that lists the current price and

availability of each item that is for sale.

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-Using technologies for developing web pages that include dynamic content.

-Developing web based applications which can produce web pages that contain information that is

connection-dependent or time-dependent.

Dynamic Web Content Technologies Evolution

Dynamic web content development technologies have evolved through time in speed, security, ease of use

and complexity. Initially C based CGI programs were on the server Then template based technologies like

ASP and PHP were then introduced which allowed ease of use for designing complex web pages. Sun Java

introduced Servlets and JSP that provided more speed and security as well as better tools for web page

creation.

Figure 7: Dynamic web content technologies evolution

Layers and Web Application

Normally web applications are partitioned into logical layers. Each layer performs a specific functionality

which should not be mixed with other layers. Layers are isolated from each other to reduce coupling

between them but they provide interfaces to communicate with each other.

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Figure 8: Simplified view of a web application and its layers

-Presentation Layer:

Provides a user interface for client to interact with application. This is the only part of application

visible to client.

-Business Layer

The business or service layer implements the actual business logic or functionality of the application.

For example in case of online shopping systems this layer handles transaction management.

-Data Layer

This layer consists of objects that represent real-world business objects such as an Order,

OrderLineItem, Product, and so on.

There are several Java technologies available for web application development which includes Java

Servlets, JavaServer Pages, JavaServer Faces etc.

Figure 9: Java web application technologies (presentation/web tier)

References:

Java, A Practical Guide by Umair Javed

Java tutorial by Sun: http://java.sun.com/docs/books/tutorial/

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