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Servlets- Servlet API

3.Servlet API

we can create any servlet program by using below 3 ways

1.javax.servlet.Servlet (Interface)

Servlet interface is the ROOT interface of Servlet API. It provides common behaviour to all the servlets.

Method Description
public void init(ServletConfig config) Initializes the servlet. It is the life cycle method of servlet and invoked by the web container only once.
public void service(ServletRequest req,ServletResponse response) Provides response for the incoming request. It is invoked at each request by the web container.
public void destroy() Is invoked only once and indicates that servlet is being destroyed.
public ServletConfig getServletConfig() Returns the object of ServletConfig.
public String getServletInfo() returns information about servlet such as writer, copyright, version etc.

Steps to implement Servlet program using Servlet Interface

  1. Create a Class which implements Servlet Interface

  2. Implement all 5 abstract methods

  3. Write Request Processing logic in service(req,res) method

2.javax.servlet.GenericServlet (abstract class)

  • GenericServlet class implements Servlet, ServletConfig and Serializable interfaces.

  • It provides implementation for all methods of Servlet interface except the service().

  • it is protocol-independent, so it can handle any request of any protocol

  • Create servlet by providing the implementation of the service() method.

Init(),destroy(),getServletConfig(),getservletInfo() are inherted and implemented

1. public abstract void service(ServletRequest req, ServletResponse res)

2. public void init() it is a convenient method for the servlet programmers, now there is no need to call super.init(config)

3. public ServletContext getServletContext()

4. public String getInitParameter(String name)

5. public Enumeration getInitParameterNames()

6. public String getServletName()

Steps to write Servlet Program using GenericServlet

  1. Create a Class which extends GenericServlet Interface

  2. Implement & Write Request Processing logic in service(req,res) method

3.javax.servlet.http.HttpServlet

HttpServlet class extends the GenericServlet class and implements Serializable interface. It provides http specific methods such as doGet, doPost, doHead, doTrace etc.

We have 2 service methods

  1. Public void service(ServletRequest req,ServletResponse res) dispatches the request to the protected service method by converting the request and response object into http type.

  2. protected void service(HttpServletRequest req,HttpServletResponse res) : Receives the request from the service method, and dispatches the request to the doXXX() method depending on the incoming http request type.

7 proteced doXXX (HttpServletRequest, HttpServletResponce) service methods

  1. protected void doGet(HttpServletRequest req, HttpServletResponse res)

  2. protected void doPost(HttpServletRequest req, HttpServletResponse res)

  3. protected void doHead(HttpServletRequest req, HttpServletResponse res)

  4. protected void doOptions(HttpServletRequest req, HttpServletResponse res)

  5. protected void doPut(HttpServletRequest req, HttpServletResponse res)

  6. protected void doTrace(HttpServletRequest req, HttpServletResponse res)

  7. protected void doDelete(HttpServletRequest req, HttpServletResponse res)

Steps to write Servlet Program using GenericServlet

  1. Create a Class which extends HttpServlet Interface

  2. Write Request Processing logic in service(req,res) OR Not Recommended

  3. Write Request Processing logic in doXXX(req,res) doGet,doPost Recommended

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