HttpServlet Class In Java

HttpServelt is an abstract class, it comes under package 'javax.servlet.http.HttpServlet' . To create a servlet the class must extend the HttpServlet class and override at least one of its methods (doGet, doPost, doDelete, doPut). The HttpServlet class extends the GenericServlet class and implements a Serializable interface. 

Constructor of HttpServlet Class

HttpServlet()

This is an abstract class so, the constructor does nothing.

Methods of HttpServlet Class

1. doGet() Method

• This method is used to handle the GET request on the server-side.
• This method also automatically supports HTTP HEAD (HEAD request is a GET request which returns nobody in response ) request.
• The GET type request is usually used to preprocess a request.

Modifier and Type:  protected void

Syntax:

protected void doGet(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the GET request.
• ServletException - Use to handle the GET request.

2. doPost() Method

• This method is used to handle the POST request on the server-side.
• This method allows the client to send data of unlimited length to the webserver at a time.
• The POST type request is usually used to post-process a request.

Modifier and Type:  protected void

Syntax:

protected void doPost(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameter:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Throws:

• IOException - if an input or output error is detected when the servlet handles the POST request.
• ServletException - Use to handle the POST request.

3. doHead() Method

• This method is overridden to handle the HEAD request.
• In this method, the response contains the only header but does not contain the message body.
• This method is used to improve performance (avoid computing response body).

Modifier and Type: protected void 

Syntax:

protected void doHead(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the HEAD request.
• ServletException - Use to handle the HEAD request.

4. doPut() Method

• This method is overridden to handle the PUT request.
• This method allows the client to store the information on the server(to save the image file on the server).
• This method is called by the server (via the service method) to handle a PUT request.

Modifier and Type:  protected void

Syntax:

protected void doPut(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Throws:

• IOException - if an input or output error is detected when the servlet handles the PUT request.
• ServletException - Use to handle the PUT request.

5. doDelete() Method

• This method is overridden to handle the DELETE request.
• This method allows a client to remove a document or Web page from the server.
• While using this method, it may be useful to save a copy of the affected URL in temporary storage to avoid data loss.

Modifier and Type:  protected void 

Syntax:

protected void doDelete(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the DELETErequest.
• ServletException - Use to handle the DELETE request.

6. doOptions() Method

• This method is overridden to handle the OPTIONS request.
• This method is used to determine which HTTP methods the server supports and returns an appropriate header.

Modifier and Type: protected void 

Syntax:

protected void doOptions(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the OPTIONS request.
• ServletException - Use to handle the OPTIONS request.

7. doTrace() Method

• This method is overridden to handle the TRACE request.
• This method returns the headers sent with the TRACE request to the client so that they can be used in debugging.

Modifier and Type:  protected void

Syntax:

protected void doTrace(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the TRACE request.
• ServletException - Use to handle the TRACE request.

8. getLastModified() Method

• This method returns the time the HttpServletRequest object was last modified.
• If time is unknown the method will return a negative number.
• This method makes browser and proxy caches work more effectively.
• also reducing the load on server and network resources.

Modifier and Type: protected long

Syntax:

protected long getLastModified(HttpServletRequest request)

Parameter: request - an HttpServletRequest object that contains the request the client has made of the servlet.

9. service() Method

This method receives standard HTTP requests from the public service method and dispatches them to the doXXX methods defined in this class.

Modifier and Type: protected void

Syntax:

protected void service(HttpServletRequest request, HttpServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the HTTP request.
• ServletException - Use to handle the HTTP request.

10. service() Method

This method is used to dispatch client requests to the public service method.

Modifier and Type: public void

Syntax:

public void service(ServletRequest request,ServletResponse response) 
throws ServletException,IOException

Parameters:

• request - an HttpServletRequest object that contains the request the client has made of the servlet.
• response - an HttpServletResponse object that contains the response the servlet sends to the client.

Exceptions:

• IOException - if an input or output error is detected when the servlet handles the HTTP request.
• ServletException - Use to handle the HTTP request.

Example:

package com.gfg;
import javax.servlet.*;
import javax.servlet.http.*;

// here GFGServlet class inherit HttpServlet
public class GFGServlet extends HttpServlet {

    // we are defining the doGet method of HttpServlet
    // abstract class
    public void doGet(HttpServletRequest rq,
                      HttpServletResponse rs)
    {
        // here user write code to handle doGet request
    }

    // we are defining the doPost method of HttpServlet
    // abstract class
    public void doPost(HttpServletRequest rq,
                       HttpServletResponse rs)
    {
        // here user write code to handle doPost request
    }

} // class ends

Note: This is server-side code, it is only for clarification on how to use HttpServlet class.