This document provides an overview of web applications and servlet requests and responses. It discusses the client-server model, advantages of web applications, the structure of request and response messages, common request methods, the servlet API, and the lifecycle of servlets. Key topics covered include how servlets are used to add dynamic content to web servers, the roles of GenericServlet, HttpServlet, ServletRequest, ServletResponse, and how servlets handle requests and construct responses.

1. Slide 1 of 30
Web Applications – An Overview
& Servlet Requests and Responses

2. Slide 2 of 30
Objectives
 Web Client-Server Model
 Evolution of Servlets
 Web Application
 Web Application Development Process
 Servlet API
 Sending Request
 Sending Response
 Servlet Life Cycle

3. Slide 3 of 30
Advantages of Web Application
 Easier access to information
 Lower maintenance and deployment costs
 Platform independency
 Wider visibility

4. Slide 4 of 30
Request Message Structure

5. Slide 5 of 30
Request line
 This component returns the method, resource
information, such as the type and name, and
the HTTP version of the request message.

6. Slide 6 of 30
Header information
 This component return the User-Agent along
with the Accept header

7. Slide 7 of 30
Response Message Structure

8. Slide 8 of 30
Status line
 This element indicates status of the requested
process

9. Slide 9 of 30
Header information
 The header information contains information
such as server, last modified date, content-
length and content type.

10. Slide 10 of 30
Request Method

11. Slide 11 of 30
Limitation of Web Server
 Overloading error
 Unavailability due to maintenance
 Heavy traffic
 Virus and worm attack

12. Slide 12 of 30
Servlet
 Servlet are java code that are used to add
dynamic content to Web Server
 Servlet gets auto refreshed on receiving a
request each time. A servlet initialisation code is
used only for initialising the Servlet for first
time.

13. Slide 13 of 30
Advantage of Servlet

14. Slide 14 of 30
Merits of Servlet
 Enhanced efficiency
 Ease of use
 Powerful
 Portable
 Safe and Cheap

15. Slide 15 of 30
Demerits of Servlet
 Low level HTML documentation
 UnClear session management

16. Slide 16 of 30
Web Container Concept
 The web container is a program that manage
execution of servlets and JSP Page

17. Slide 17 of 30
Web Application Servlet -JSP

18. Slide 18 of 30
Servlet API – GenericServlet Class
GenericServlet
Class implement
the Servlet and
ServletConfig

19. Slide 19 of 30
Servlet API – GenericServlet Class
 Defines a generic, protocol-independent servlet. To write an HTTP servlet for use on
the Web, extend HttpServlet instead.
 GenericServlet implements the Servlet and ServletConfig interfaces. GenericServlet
may be directly extended by a servlet, although it's more common to extend a
protocol-specific subclass such as HttpServlet.
 GenericServlet makes writing servlets easier. It provides simple versions of the
lifecycle methods init and destroy and of the methods in the ServletConfig interface.
GenericServlet also implements the log method, declared in the ServletContext
interface.
 To write a generic servlet, you need only override the abstract service method.

20. Slide 20 of 30
“HttpServlet” Class
 The HttpServlet class provider an abstract class
a create an HTTP Servlet. HttpServlet extend
the GenericServlet
 Two Method process Request
– dopost()
– doget()

21. Slide 21 of 30
ServletRequest
This interface is for getting data from the client to
the servlet for a service request
 getParameter()
 getAttribute()
 getContentLength()
 getInputStream()
 getServerName()

22. Slide 22 of 30
HttpServletRequest
HttpServletRequest
extend ServletRequest

23. Slide 23 of 30
Method of HttpServletRequest Interface
 getCookies()
 getHeader()
 getMethod()
 getPathInfo()
 getAuthType()
 getParametter()
 getParametterNames()
 getParametterValues()

24. Slide 24 of 30
Request Header
 Accept
 Accept-Charset
 Accept-Encoding
 Accept-Language
 Authorization

25. Slide 25 of 30
Request Header
 getHeader()
 getHeaders()
 getHeaderNames()

26. Slide 26 of 30
“ServletResponse” Interface
 The ServletResponse interface define methods
that allow you to retrieve an out put stream to
send data to the Client

27. Slide 27 of 30
Method of “ServletResponses” Interface
 getContentType()
 getWriter()
 getOutputStream()
 setContentType()

28. Slide 28 of 30
“HttpServletResponse” Interface
Extend ServletReponse
 addCookie()
 addHeader()
 containtHeader()
 sendError()
 Print()
 sendRedirect()
 encodeRedirect()

29. Slide 29 of 30
Stage of Servlet Life Cycle
Instatiation
Initialisation
Service
Destroy
Unavaible
The servlet
container create
an object of the
Servlet class

30. Slide 30 of 30
Summary
 Web Client-Server Model
 Evolution of Servlets
 Web Application
 Web Application Development Process
 Servlet API
 Sending Request
 Sending Response
 Servlet Life Cycle