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Where are we?
JAVA

Introduction Object-oriented design Advanced topics Server-side coding

4. Object 10. JDBC
1. Intro to
Java, Course Classes 7. Inheritance 11.Streams

2. Java lang. 6. Exception 13. Servlets
5. Encapsulation
basics Handling
14. JSP
3. Arrays 8. Polymorphism
12. Networking
9. Abstract classes
and Interfaces

Newbie Programmers Designers Developers Professionals

HTTP
Request

Request

<html>
<head>
<body>
<html>
…
<head>
<body>
…

Client
Response
HTTP

HTML

Why Build Web Pages Dynamically?
 The Web page is based on data submitted by the
user
 E.g., results page from search engines
 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 sources
 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.

HTTP Request HTTP Response

Key elements of a “request” Key elements of a “response”
stream: stream:

 HTTP method (action to be  A status code (for whether
performed). the request was successful).

 The page to access (a URL).  Content-type (text, picture,
html, etc…).
 Form parameters.
 The content ( the actual
content).

Introduction – What is a Servlet

• Where does Servlet come into the picture?
I can serve only
static HTML
pages
Web Server
Application

Dude ,Not a
problem. I
can handle
dynamic
Helper requests.
Application
Web Server machine

“The Helper Application is nothing but a SERVLET”

What is java servlet ?
A servlet is a small Java program that runs within a Web server. Servlets
receive and respond to requests from Web clients, usually across HTTP,
the HyperText Transfer Protocol. Servlet is an opposite of applet as a
server-side applet. Applet is an application running on client while servlet
is running on server.
Request

Servlet

Client Response Server

Example use of servlet

 Processing data POST over HTTPs using HTML form as purchase
order or credit card data
 Allowing collaborative between people such as on-line
conferencing

Application/Browser Web Server Database/ FileSystem
(User Interface) (Application Logic) (Persistent Storage)

Why Use Servlets ?
 One of the reasons that Java became
popular is Applets.
– but there are problems with Applets
• Browser compatibility

 Server-side Java
– the code is executed on the server side not the client
side
– a dynamically loaded module that services requests
from a Web server

Servlets (contd.)
– vs. Common Gateway Interface (CGI)
• create new process for each request
– most platform independent CGI language - Perl
• start a new instance of interpreter for every request
• CGI runs in a completely separate process from the Web
server
– vs. Server-Side JavaScript
• only available on certain web servers
– vs. Active Server Pages (ASP)
• only available on certain web servers

Servlet Architecture -Web Container

• What is a Web Container?

request
GET.
GET. GET.
….. ….. …..

Web Web Servlet
Server Container
Client

Servlet Architecture – Web Container

• How does the Container handle a request?

request Servlet
Http request Web
Container <Html>
<Body>
response …….
</Body>
Thread </Html>
Web
Server

response Service()
Client

doGet()

Servlet Architecture – Web Container

The CONTAINER
• What is the role of Web Container ?
S2

• Communication Support S1

• Lifecycle Management
JSP1
Multi-threading support
S3
• Security

S4
• JSP Support

The container can contain multiple Servlets & JSPs within it

Example for Servers: Netscape Web servers
Microsoft's Internet Information Server (IIS),
the World Wide Web Consortium's Jigsaw Web server

Developer(s) Apache Software Foundation

Stable release 7.0.37
(February 18, 2013;)

Preview release Non [±]

Development status Active

Written in Java

Operating system Cross-platform

Type Servlet container
HTTP web server

License Apache License 2.0

Website tomcat.apache.org/

Apache


Apache is a very popular server
Apache is a very popular server


66% of the web sites on the Internet use Apache
66% of the web sites on the Internet use Apache
 Apache is:
 Apache is:
 Full-featured and extensible
 Full-featured and extensible
 Efficient
 Efficient
 Robust
 Robust
 Secure (at least, more secure than other servers)

 Secure (at least, current standards other servers)
 Up to date with more secure than

 Up to date with current standards
 Open source

 Free source
Open
 Why use anything else?
 Free

3
3

• Before you can program with servlets, you must
download and install the Apache group's
implementation of servlets called Tomcat.
• Install the Tomcat with specific port number(default
is 8080
• If the installation is successful, you get the Tomcat’s
home page

Servlet Lifecycle

• The Servlet lifecycle is simple, there is only one main state –
“Initialized”.

Does not exist

The container calls destroy()
the init() before the init()
servlet can service
When a new request
any client requests.
for that servlet
comes in.
To initialize your
Initialized To determine which
servlet before
HTTP method
handling any client
Service() should be called.
requests.

Servlet Lifecycle - Hierarchy

Interface Servlet

•
Abstract class GenericServlet If not overridden, implements init()
method from the ‘Servlet’ interface,

Abstract class HttpServlet If not overridden, implements service()
method.

Concrete class Your Servlet We implement the HTTP methods
here.

Object model of Servlet Framework
<<Interface>> <<Interface>>
javax.servlet.Servlet javax.servlet.ServletConfig
init( ) javax.servlet.GenericServlet
getInitParameter( )
getServletConfig( )
init( ) getServletContext( )
service( )
getServletConfig( ) getInitParameterNames( )
getServletInfo( )
service( ) getServletName( )
destroy( )
getServletInfo( )
destroy( )
getInitParameter( )
getServletContext( )
getInitParameterNames( )
getServletName( )
log( )

javax.servlet.http.HttpServlet
doDelete( )
doGet( )
doOptions( )
doPost( )
doPut( )
doTrace( )
getLastModified( )
service( )

Basic Servlet

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class HelloServlet extends HttpServlet
{
public void doGet(HttpServletRequest request,
HttpServletResponse response)throws
ServletException,IOException

Request and Response – GET v/s POST

 The HTTP request method determines whether doGet() or
doPost() runs.
GET (doGet()) POST (doPost())

The request contains only the Along with request line
HTTP Request request line and HTTP header. and header it also contains
HTTP body.
Parameter The form elements are passed The form elements are
passing to the server by appending at passed in the body of the
the end of the URL. HTTP request.
Size The parameter data is limited Can send huge amount of
(the limit depends on the data to the server.
container)

Usage Generally used to fetch some Generally used to process
information from the host. the sent data.

import java.io.*;

{
public void doGet(HttpServletRequest request, HttpServletResponse
response)throws ServletException,IOException
{
response.setContentType("text/html");

HttpServletResponse Interface

 void setContentType( String type )
Specifies the MIME( Multipurpose Internet Mail
Extensions) type of the response to the browser.
The MIME type helps the browser determine how to
display the data (or possibly what other application to
execute to process the data).
 For example, MIME type "text/html" indicates that
the response is an HTML document, so the browser
displays the HTML page.

import java.io.*;

{
{
PrintWriter out = response.getWriter();

ServletOutputStream getOutputStream()
Obtains a byte-based output stream enabling binary data to be sent
to the client.

PrintWriter getWriter()
Obtains a character-based output stream enabling text data to be
sent to the client.

import java.io.*;

{
{
PrintWriter out = response.getWriter();

out.println("<html><head><title>Hello World</title></head>");
out.println("<body><h1>Hello World</h1></body></html>");

}
}

Servlet Architecture – Deployment Descriptor

 How does the Container know which Servlet the client has
requested for?

A Servlet can have 3 names
<web-app>
………
 Client known URL name <servlet>
<servlet-name>Hello</servlet-name>
<servlet-class>HelloServlet</servlet-class>
 Deployer known secret </servlet>
internal name
<servlet-mapping>
 Actual file name <url-pattern>/HelloNova</url-pattern>
</servlet-mapping>
………..
………..
</web-app>
Web.xml

<web-app>
………
<servlet>
<servlet-class>HelloServlet</servlet-class>
</servlet>

<servlet-mapping>
<url-pattern>/HelloNova</url-pattern>
</servlet-mapping>
………..
………..
</web-app>

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