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15.1 Forwarding Requests

357

The Servlet 2.2 specification adds a third way to send data to the destina 

tion page when using 

GET

 requests: simply append the query data to the

URL. For example, 

String address = "/path/resource.jsp?newParam=value";

RequestDispatcher dispatcher =

getServletContext().getRequestDispatcher(address);

dispatcher.forward(request, response);

This technique results in an additional request parameter of 

newParam

(with a value of 

value

) being added to whatever request parameters already

existed. The new parameter is added to the beginning of the query data so

that it will replace existing values if the destination page uses 

getParameter

(use the first occurrence of the named parameter) rather than 

get 

ParameterValues

 (use all occurrences of the named parameter).

Interpreting Relative URLs in the Destination 

Page

Although a servlet can forward the request to arbitrary locations on the same

server, the process is quite different from that of using the 

sendRedirect

method of 

HttpServletResponse

 (see Section 6.1). First, 

sendRedirect

requires the client to reconnect to the new resource, whereas the 

forward

method of 

RequestDispatcher

 is handled completely on the server. Sec 

ond, 

sendRedirect

 does not automatically preserve all of the request data;

forward

 does. Third, 

sendRedirect

 results in a different final URL,

whereas with 

forward,

 the URL of the original servlet is maintained.

This final point means that, if the destination page uses relative URLs for

images or style sheets, it needs to make them relative to the server root, not

to the destination page's actual location. For example, consider the following

style sheet entry: