Java HttpServlet Class

HttpServlet class:

HttpServlet class extends the GenericServlet. It is protocol-dependent.

public abstract class HttpServlet extends GenericServlet

HttpServlet class is in javax.servlet.http package (javax.servlet.http.HttpServlet).

Methods of HttpServlet class:

1. service(ServletRequest req,ServletResponse res): Dispatches the requests to the protected service method. It converts the request and response object into HTTP type before dispatching the request.

Syntax:

public void service(ServletRequest req, ServletResponse res) 
throws ServletException, IOException

2. service(HttpServletRequest req, HttpServletResponse res): Receives HTTP requests from the public service method and dispatches the request to the doXXX methods defined in this class.

Syntax:

protected void service(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

3. doGet(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling GET requests.

Syntax:

protected void doGet(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

4. doPost(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling POST requests.

Syntax:

protected void doPost(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

5. doHead(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling HEAD requests.

Syntax:

protected void doHead(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

6. doOptions(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling OPTIONS requests.

Syntax:

protected void doOptions(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

7. doPut(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling PUT requests.

Syntax:

protected void doPut(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

8. doTrace(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling TRACE requests.

Syntax:

protected void doTrace(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

9. doDelete(HttpServletRequest req, HttpServletResponse res): This method is called by the web container for handling DELETE requests.

Syntax:

protected void doDelete(HttpServletRequest req, HttpServletResponse res) 
throws ServletException,IOException

10. getLastModified(HttpServletRequest req): It returns the time the HttpServletRequest object was last modified since midnight January 1, 1970 GMT. It returns a negative number if the time is unknown.

Syntax:

protected long getLastModified(HttpServletRequest req)

Servlet “Hello World” example by extending the HttpServlet class.

HelloWorld.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class HelloWorld extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    //no-argument constructor.
    public HelloWorld() {
       
    }
    
    protected void doGet(HttpServletRequest request, HttpServletResponse 
             response) throws ServletException, IOException {
	response.setContentType("text/html");
	PrintWriter out = response.getWriter();
		
        out.println("Hello World using HttpServlet class.");
        out.close();
    }
}

web.xml

<!--?xml version="1.0" encoding="UTF-8"?-->
<web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemalocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    
    <servlet>
        <servlet-name>HelloWorld</servlet-name>
        <servlet-class>
          com.w3schools.business.HelloWorld
        </servlet-class>
    </servlet>
    
    <servlet-mapping>
        <servlet-name>HelloWorld</servlet-name>
        <url-pattern>/HelloWorld</url-pattern>
    </servlet-mapping>
    
</web-app>