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Web Applications – An Overview& Servlet Requests and Responses

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Objectives Web Client-Server Model Evolution of Servlets Web Application Web Application Development Process Servlet API Sending Request Sending Response Servlet Life Cycle

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Advantages of Web Application

Easier access to information Lower maintenance and deployment costs Platform independency Wider visibility

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Request Message Structure

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Request line This component returns the method, resource

information, such as the type and name, and the HTTP version of the request message.

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Header information This component return the User-Agent along

with the Accept header

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Response Message Structure

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Status line This element indicates status of the requested

process

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Header information The header information contains information

such as server, last modified date, content-length and content type.

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Request Method

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Limitation of Web Server Overloading error Unavailability due to maintenance Heavy traffic Virus and worm attack

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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.

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Advantage of Servlet

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Merits of Servlet Enhanced efficiency Ease of use Powerful Portable Safe and Cheap

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Demerits of Servlet Low level HTML documentation UnClear session management

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Web Container Concept The web container is a program that manage

execution of servlets and JSP Page

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Web Application Servlet -JSP

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Servlet API – GenericServlet Class

GenericServlet Class implement the Servlet and ServletConfig

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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.

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“HttpServlet” Class The HttpServlet class provider an abstract class

a create an HTTP Servlet. HttpServlet extend the GenericServlet

Two Method process Request– dopost()– doget()

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ServletRequestThis interface is for getting data from the client to

the servlet for a service request getParameter() getAttribute() getContentLength() getInputStream() getServerName()

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HttpServletRequest

HttpServletRequest extend ServletRequest

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Method of HttpServletRequest Interface

getCookies() getHeader() getMethod() getPathInfo() getAuthType() getParametter() getParametterNames() getParametterValues()

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Request Header Accept Accept-Charset Accept-Encoding Accept-Language Authorization

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Request Header getHeader() getHeaders() getHeaderNames()

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“ServletResponse” Interface The ServletResponse interface define methods

that allow you to retrieve an out put stream to send data to the Client

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Method of “ServletResponses” Interface

getContentType() getWriter() getOutputStream() setContentType()

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“HttpServletResponse” Interface

Extend ServletReponse addCookie() addHeader() containtHeader() sendError() Print() sendRedirect() encodeRedirect()

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Stage of Servlet Life Cycle

Instatiation

Initialisation

Service

Destroy

Unavaible

The servlet container create an object of the Servlet class

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