Servlet - RequestDispatcher

The RequestDispatcher is an Interface that comes under package javax.servlet. Using this interface we get an object in servlet after receiving the request. Using the RequestDispatcher object we send a request to other resources which include (servlet, HTML file, or JSP file). A RequestDispatcher object can be used to forward a request to the resource or to include the resource in a response. The resource can be dynamic or static.

How to Create an Object of RequestDispatcher?

There are three ways to get an object:

1. RequestDispatcher requestDispatcher=ServletContext.getRequestDispatcher(String path);

Description:

• public interface ServletContext. Defines a set of methods that a servlet uses to communicate with its servlet container.
• path is a string specifying the pathname to the resource(servlet, HTML file, or JSP file).

2. RequestDispatcher requestDispatcher=ServletContext.getNamedDispatcher(String name);

Description:

• public interface ServletContext. Defines a set of methods that a servlet uses to communicate with its servlet container.
• name is a string specifying the name of a servlet to wrap.

3. RequestDispatcher requestDispatcher=request.getRequestDispatcher("String path");

Description:

• request is the HttpServletRequest type object.
• path is a string specifying the pathname to the resource. If it is relative, it must be relative to the current servlet.

Method and Description 

The class contains two methods:

1. forward

Syntax:

void forward(ServletRequest request,ServletResponse response) throws ServletException,IOException

Description:

• Modifier and Type:- void
• This method is used to forward a request from a servlet to another resource (servlet, JSP file, or HTML file) on the server.
• The method get called before the response has been sent to the client. If the response is already sent then the method will throws an IllegalStateException.
• The parameter request(HttpServletRequest type) and response(HttpServletResponse type) are the same objects as were passed to the calling servlet's service method.
• This method sets the dispatcher type of the given request to DispatcherType.FORWARD.

Example: 

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

public class GFG extends HttpServlet {
    public void doPost(HttpServletRequest request,
                       HttpServletResponse response)
    {
        // Perform all the work as per your
          // application's architecture
        try {
            RequestDispatcher requestDispatcher;

            // path is a string specifying the pathname to
            // the resource. If it is relative, it must be
            // relative against the current servlet
            requestDispatcher=request.getRequestDispatcher("path");
            requestDispatcher.forward(request, response);
        }
        catch (ServletException servletException) {
        }
        catch (IOException ioException) {
        }
        catch (IllegalStateException illegalStateException) {
        }
    } 
}

Note: The above code will not run in online IDE this is server-side code.

2. include

Syntax:

void include(ServletRequest request,ServletResponse response) throws ServletException,IOException

Description:

• Modifier and Type:- void
• This method is used to include the response of resource(for which the request passed servlet, JSP page, HTML file) in the current servlet response.
• The parameter request(HttpServletRequest type) and response(HttpServletResponse type) are the same objects as were passed to the calling servlet's service method.
• This method sets the dispatcher type of the given request to DispatcherType.INCLUDE.

Example: 

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

public class GFG extends HttpServlet {
    public void doPost(HttpServletRequest request,
                       HttpServletResponse response)
    {
        // Perform all the work as
        // per your application's architecture
        try {
            RequestDispatcher requestDispatcher;

            // path is a string specifying the pathname to
            // the resource. If it is relative, it must be
            // relative against the current servlet
            requestDispatcher=request.getRequestDispatcher("path");
            requestDispatcher.include(request, response);
        }
        catch (ServletException servletException) {
        }
        catch (IOException ioException) {
        }
    } 
} 

Note: The above code will not run in online IDE this is server-side code.

Fields and Description