在通过请求分派器转发的servlet中使用sendRedirect

Question

I have a filter that implements a custom convention for loading servlets and JSPs. In that convention I am using the following code to include the servlet:

servletContext
    .getRequestDispatcher( uriDispatcherLocator.getServletLocation( uri ) )
    .include( request, response );

and the following code to include the JSP (in the same filter):

servletContext
    .getRequestDispatcher( "/index.jsp" )
    .include( request, response );

Everything works fine, the servlet executes, then it includes the JSP and some irrelevant custom rules take place. As you can see, at the very moment I include a servlet with request dispatcher I cannot send an http header response to the client . The problem is that I want the servlet to have full control of the response as if it was called from inside the filter (because the filter will do nothing else than dinamically mapping the servlets according to their respective Class/JSP location in the project file system). I can use .forward() instead of .include() , but if I do I will not be able to include a JSP after the servlet has been executed.

So, how would I allow the servlet to execute the code below when being included through a filter via RequestDispatcher interface?

response.sendRedirect( "/somePath" );

No Javascript hacks, I am willing to send the proper HTTP response from the server to make the browser behave correctly.

--

EDIT: In other words:

I want to change the headers sent to the client from INSIDE an included servlet by using RequestDispatcher, but the docs states:

The included servlet cannot change the response status code or set headers; any attempt to make a change is ignored.

Answer 1

Your Filter includes your servlet

servletContext
    .getRequestDispatcher( uriDispatcherLocator.getServletLocation( uri ) )
    .include( request, response );

Your Servlet indicates it wants to redirect

request.setAttribute ("sendRedirect", "/some/path");

or, wishes to add one or more response headers

Map<String, String> respHeaders = new HashMap<String, String>();
respHeaders.put("Expires", "0");
respHeaders.put("Cache-Control", "no-cache");
request.setAttribute("respHeaders", respHeaders);

Your Filter checks for these special requests

Map<String, String> respHeaders =
                   (Map<String, String>) request.getAttribute("respHeaders");
for (String key : respHeaders.keySet()) {
    response.setHeader(key, respHeaders.get(key)); // set response headers
}

String sendRedirect;
if ((sendRedirect = (String) request.getAttribute("sendRedirect")) != null) {
    response.sendRedirect(sendRedirect); // redirect the client
}

EDIT : Perhaps some of your servlets are already driving the flow and setting response headers when called from outside an include. But, there's no way to reuse them as is. You can't simply include them and expect the same behaviour because the goal of a RequestDispatcher#include() is to provide for server-side includes (SSI) only.

Hence, we do not find any overloaded methods (or any setters that could modify this behaviour) in the API. If you want to include such servlets and retain their behaviour (like redirects) you would have to pass them a hint that they're running under an include context and so should submit their response requests.

request.setAttribute ("includeContext", true);