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SSSSSS

Java ServletsJava Servlets

By,

Kshirsagar Harshada Mangesh.

Third Year Computer

Government Polytechnic, Pune.

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What are Servlets?

What are Servlets?

Why are

Servlets?

Why are

Servlets?

How are Servlets?How are Servlets?

Why not CGI?Why not CGI?

When are

Servlets?

When are

Servlets?

Where are

Servlets?

Where are

Servlets?

Some Questions In your Mind…. Servlets

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Concepts

Internet : network of networks

WWW (World Wide Web) also referred to as web :

- One of the largest Internet services - Consists of millions of websites

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How web works

Web Browser

WebServer

URLBrowser requests

A web page

WebServer sends backthe requested page

Uniform Resource Locator which specifies the location of the webpage on the webserver

http://www.rediff.com/index.html

Stores the WebPages & sends themto the browser upon a request

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Serving static HTML page

WebServer

Browser requestsA web page

WebServer sends backthe requested page

Initially web servers were designed to provide the static WebPages

HTMLpage

WebPagesOn

Hard Disk

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Servlets

Kshirsagar Harshada Mangesh

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Servlets

Kshirsagar Harshada Mangesh

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Servlets

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Servlets

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a soultion for dynamically generating HTML

• Servlets are small platform-independent server-side programs that extend the functionality of a webserver

• It is a java class which run on the webserver and communicate with the web browser using HTML & HTTP

• A no of servlets can form a website.

Servlets

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But web consists of millions of websites( comprising of billions of webpages linked together using hyperlinks)

So there require someone to host these websites & map web applications to servlets.

This task of hosting servlets & web applications is done by

Servlets

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Architecture of a Servlet (Request-Response Flow)

WebBrowser

WebServer

HTTPRequest

HTTPResponse

Mappinginformation

Web Application

WebContainer

Staticresources

Servlets

Static resources

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init() destroy()Servlet

3 distinct phasesBirthLifeDeath

service()

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init() method

• called before the servlet handles its first request• The container passes ServletConfig Object contaning the

initialization parameters to this method• If overridden must call super.init() first

public void init(ServletConfig config)throws SerletException

{

}

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service() method

• Each time the server receives a request for a servlet,it spawns a new thread & calls the service method

• It is the entry point for executing application logic in a servlet

WebServer

Browser

Browser

Browser

service()

service()

service()

SingleInstance

Of theservlet

public void service(ServletRequest request,ServletResponse response){

}

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destroy() method

- is called at servlet unloading

- all cleanup activities can be done here (closing db/socket connections,updating log files)

public void destroy(){

}

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There are 2 steps in order to build & deploy a servlet-based application

(A) Development Phase : - Write the servlet class with the required application logic- Compile the servlet class

(B) Deployment Phase :- Deploy the servlet in the webserver

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Redirection• At times outdated/old URLs need to be redirected to new ones

so that the user does not see an error when the URL is accessed

• In such situations,URL redirection option allow us to forward the request to new location

Several situations in which the URL needs to be changed- when the document moves to new URL- when the application is enhanced to include more pages- when the user goes to final order page w/o filling the requisite order details

URL redirection can be achieved by using(A) sendRedirect method of HttpServletResponse interface(B) forward method of RequestDispatcher interface

“redirect” means sending response from servlet to the browser

telling it to go to another URL

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Conclusion

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Question & Answers

??

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Java on Server-side • Robust• Scalable• Open• Fast• Portable• Well integrated• Extensible & flexible

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Advantages over other techniques

• Generally much faster than CGI scripts

• A different process model is used.• Standard API• Supported by many web servers.• All the advantages of the Java--Ease of development--Large API

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Session Tracking