Is it mandatory to have a doGet or doPost method?

Question

I have few questions.

1. Can i have a Servlet without these two methods?
2. Can i call my form directly to Service method... Like

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 FormServlet extends HttpServlet {

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

}

Answer 1

1. Yes, you can have a servlet without either of these methods (they have no implementation). Still having a HttpServlet without having doGet/doPost seems a bit pointless, since servlet can only communicate with the a limited number of request methods such as GET, POST, DELETE, PUT (for more see specification section 5.1.1 ).
2. HttpServlet don't have doService methods. If you meant void service() then I advise you not to mess with it unless you really know what you're doing. If all you need is to use doService call it from doGet, doPost (as someone already suggested).

Ok, examples:

public class DoesNothingServlet extends HttpServlet {} //does what the name implies

public class FormServlet extends HttpServlet { //what you want to do

  protected doGet(HttpServletRequest request, HttpServletResponse response) throws   ServletException, IOException {
        doService(request,response)
  }

  protected void doService (HttpServletRequest request, HttpServletResponse response) throws   ServletException, IOException {
        //Do something
  }

}

Answer 2

No, it's not mandatory. Since HttpServlet is an abstract class, there are abstract implementations of all doXXX methods, and you don't have to implement them if you don't want to.

Answer 3

Read http://download.oracle.com/docs/cd/E17802_01/webservices/webservices/docs/1.6/api/javax/servlet/http/HttpServlet.html

Provides an abstract class to be subclassed to create an HTTP servlet suitable for a Web site. A subclass of HttpServlet must override at least one method, usually one of these:

• doGet, if the servlet supports HTTP GET requests
• doPost, for HTTP POST requests
• doPut, for HTTP PUT requests
• doDelete, for HTTP DELETE requests
• init and destroy, to manage resources that are held for the life of the servlet
• getServletInfo, which the servlet uses to provide information about itself

From your doGet and doPost methods, you can call your doService(..,..) method if you wish.

Answer 4

You will note that the service() method originates from the javax.servlet.GenericServlet and not javax.servlet.http.HttpServlet.

If you want to do something with a servlet which doesn't involve the http protocol, I would say go ahead.

In the Head First Servlets and JSP they explain this in detail. 99% You will make use of the HttpServlet.

By extending GenericServlet, the servlet would run regardless of the content submitted. As long as the URL is fired the service() method will execute.

Answer 5

My understanding, if I got you correct, is you want your HTTP GET, POST, (PUT, DELETE) to call your doService method. If that's the case, you can do this.

protected doGet(HttpServletRequest request, HttpServletResponse response) throws   ServletException, IOException {
        doService(request,response)
  }

protected doPost(HttpServletRequest request, HttpServletResponse response) throws   ServletException, IOException {
        doService(request,response)
  }

If you extends HttpServlet you don't have to override doGet and doPost as it's already implemented by HttpServlet. Servlet request get handled by the service() method which then (based on the HTTP request method) calls its relevant doXXX method.

I wouldn't mess with the service() method though, unless you know what you're doing.