The Forward Method
The forward method of the RequestDispatcher interface may be called by the calling servlet only when no output has been committed to the client. If output data exists in the response buffer that has not been committed, the content must be cleared before the target servlet’s service method is called. If the response has been committed, an IllegalStateException must be thrown.
The path elements of the request object exposed to the target servlet must reflect the path used to obtain the RequestDispatcher.
The only exception to this is if the RequestDispatcher was obtained via the getNamedDispatcher method. In this case, the path elements of the request object must reflect those of the original request.
Before the forward method of the RequestDispatcher interface returns, the response content must be sent and committed, and closed by the servlet container.
The path elements of the request object exposed to the target servlet must reflect the path used to obtain the RequestDispatcher.
The only exception to this is if the RequestDispatcher was obtained via the getNamedDispatcher method. In this case, the path elements of the request object must reflect those of the original request.
Before the forward method of the RequestDispatcher interface returns, the response content must be sent and committed, and closed by the servlet container.
=> Query String
The request dispatching mechanism is responsible for aggregating query string parameters when forwarding or including requests.
=> Forwarded Request Parameters
Except for servlets obtained by using the getNamedDispatcher method, a servlet that has been invoked by another servlet using the forward method of RequestDispatcher has access to the path of the original request.
The following request attributes must be set:
javax.servlet.forward.request_uri
javax.servlet.forward.context_path
javax.servlet.forward.servlet_path
javax.servlet.forward.path_info
javax.servlet.forward.query_string
The values of these attributes must be equal to the return values of the HttpServletRequest methods getRequestURI, getContextPath, getServletPath, getPathInfo, getQueryString respectively, invoked on the request object passed to the first servlet object in the call chain that received the request from the client.
These attributes are accessible from the forwarded servlet via the getAttribute method on the request object. Note that these attributes must always reflect the information in the original request even under the situation that multiple forwards and subsequent includes are called.
If the forwarded servlet was obtained by using the getNamedDispatcher method, these attributes must not be set.
The following request attributes must be set:
javax.servlet.forward.request_uri
javax.servlet.forward.context_path
javax.servlet.forward.servlet_path
javax.servlet.forward.path_info
javax.servlet.forward.query_string
The values of these attributes must be equal to the return values of the HttpServletRequest methods getRequestURI, getContextPath, getServletPath, getPathInfo, getQueryString respectively, invoked on the request object passed to the first servlet object in the call chain that received the request from the client.
These attributes are accessible from the forwarded servlet via the getAttribute method on the request object. Note that these attributes must always reflect the information in the original request even under the situation that multiple forwards and subsequent includes are called.
If the forwarded servlet was obtained by using the getNamedDispatcher method, these attributes must not be set.
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