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15.1 Forwarding Requests

355

Listing 15.1 Request Forwarding Example

public void doGet(HttpServletRequest request,

                  HttpServletResponse response)

    throws ServletException, IOException {

  String operation = request.getParameter("operation");

  if (operation == null) {

    operation = "unknown";

  }

  if (operation.equals("operation1")) {

    gotoPage("/operations/presentation1.jsp",

             request, response);

  } else if (operation.equals("operation2")) {

    gotoPage("/operations/presentation2.jsp",

             request, response);

  } else {

    gotoPage("/operations/unknownRequestHandler.jsp",

             request, response);

  }

}

private void gotoPage(String address,

                      HttpServletRequest request,

                      HttpServletResponse response)

    throws ServletException, IOException {

  RequestDispatcher dispatcher =

    getServletContext().getRequestDispatcher(address);

  dispatcher.forward(request, response);

}

argument to 

getRequestDispatcher

. However, since forwarded requests

use the same request method as the original request, 

POST

 requests cannot

be forwarded to normal HTML pages. The solution to this problem is to sim 

ply rename the HTML page to have a 

.jsp

 extension. Renaming 

some 

file.html

 to 

somefile.jsp

 does not change its output for 

GET

 requests,

but 

somefile.html

 cannot handle 

POST

 requests, whereas 

somefile.jsp

gives an identical response for both 

GET

 and 

POST

.

Supplying Information to the Destination Pages

To forward the request to a JSP page, a servlet merely needs to obtain a

RequestDispatcher

 by calling the 

getRequestDispatcher

 method of

ServletContext

, then call 

forward

 on the result, supplying the 

Http 

ServletRequest

 and 

HttpServletResponse

 as arguments. That's fine as

far as it goes, but this approach requires the destination page to read the

Second edition of this book: www.coreservlets.com; Sequel: www.moreservlets.com.

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