RequestDispatcher by R4R Team

4)RequestDispatcher:

RequestDispatcher is an interface, implementation of which defines an object which can dispatch request to any resources(such as HTML, Image, Jsp, Servlet) on the server.
Method of RequestDispatcher:

RequestDispatcher interface provides two important methods:
 

Methods Description
void forward(ServletRequest request, ServletResponse response)
 
 forwards a request from a servlet to another resource (servlet, JSP file, or HTML file) on the server
void include(ServletRequest request, ServletResponse response)  includes the content of a resource (servlet, JSP page, HTML file) in the response

How to get an object of RequestDispatcher:

getRequestDispatcher() method of ServletRequest returns the object of RequestDispatcher.

RequestDispatcher rs = request.getRequestDispatcher("hello.html");
rs.forward(request,response);

or

RequestDispatcher rs = request.getRequestDispatcher("hello.html");
rs.include(request,response);

Example

In this example, we will show how RequestDispatcher is used to forward or include response of a resource in a servlet. Here we are using index.html to get username and password from the user, Validate servlet will validate the password entered by the user, if the user has entered "r4r" as password, then he will be forwarded to Welcome servlet else the index.html will be shown again to the user.

Files to be created

index.html will have form field to get user information
Validate.java will validate the data entered by the user
hello.java will be the welcome page
web.xml

index.html:

<form method="post" action="Validate">

Name:<input type="text" name="user" /><br/>

Password:<input type="password" name="pass" ><br/>

<input type="submit" value="submit">

</form>

Validate.java

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class Validate extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html;charset=UTF-8");

PrintWriter out = response.getWriter();

try {

String name = request.getParameter("user");

String password = request.getParameter("pass");

if(password.equals("r4r"))

{

RequestDispatcher rd = request.getRequestDispatcher("hello");

rd.forward(request, response);

}

else

{

out.println("<font color='red'><b>You have entered incorrect password</b></font>");

RequestDispatcher rd = request.getRequestDispatcher("index.html");

rd.include(request, response);

}

}finally {

out.close();}}}

hello.java:

import java.io.*;

import javax.servlet.*;

import javax.servlet.http.*;

public class Welcome extends HttpServlet {

protected void doPost(HttpServletRequest request, HttpServletResponse response)

throws ServletException, IOException {

response.setContentType("text/html;charset=UTF-8");

PrintWriter out = response.getWriter();

try {

out.println("<h2>Welcome user</h2>");

} finally {

out.close();

}}}

web.xml:

<web-app>

<servlet>

<servlet-name>Validate</servlet-name>

<servlet-class>Validate</servlet-class>

</servlet>

<servlet>

<servlet-name>Welcome</servlet-name>

<servlet-class>Welcome</servlet-class>

</servlet>

<servlet-mapping>

<servlet-name>Validate</servlet-name>

<url-pattern>/Validate</url-pattern>

</servlet-mapping>

<servlet-mapping>

<servlet-name>Welcome</servlet-name>

<url-pattern>/Welcome</url-pattern>

</servlet-mapping>

<welcome-file-list>

<welcome-file>index.html</welcome-file>

</welcome-file-list>

</web-app>

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