Servlet Controller Dispatcher : RequestDispatcher « Servlet « Java Tutorial

1. Java Tutorial
2. Servlet
3. RequestDispatcher

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;

public class MyServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, 
        HttpServletResponse response) 
         throws ServletException, java.io.IOException {

        RequestDispatcher dispatcher = null;
        String param = request.getParameter("go");
             if (param == null)
                 throw new 
                     ServletException("Missing parameter in Controller.");
             else if (param.equals("weather"))
                 dispatcher = getServletContext().
                     getNamedDispatcher("Weather");
             else if (param.equals("maps"))
                 dispatcher = getServletContext().
                     getNamedDispatcher("Maps");
            else
                throw new ServletException(
                    "Improper parameter passed to Controller.");
         /*check for a null dispatcher, then 
            dispatch the request to the correct URL*/
        if (dispatcher != null)
            dispatcher.forward(request,response);
        else
            throw new ServletException(
              "Controller received a null dispatcher.");
    }
}

<?xml version="1.0" encoding="ISO-8859-1"?>

<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.2//EN"
    "http://java.sun.com/j2ee/dtds/web-app_2_2.dtd">

<web-app>
    <servlet><servlet-name>MyServletName</servlet-name>
             <servlet-class>MyServlet</servlet-class>
        <init-param>
            <param-name>
                go
            </param-name>
            <param-value>
                weather
            </param-value>
        </init-param>
             
    </servlet>
    
    <servlet-mapping><servlet-name>MyServletName</servlet-name>
        <url-pattern>/index.html</url-pattern>
    </servlet-mapping>
</web-app>

25.14.RequestDispatcher
	25.14.1.	Servlet Forwarding Dispatch
	25.14.2.	Servlet Controller Dispatcher