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From Jan Luehe <Jan.Lu...@Sun.COM>
Subject Re: Response not flushed before RD.forward() returns
Date Fri, 20 Jan 2006 04:40:56 GMT


Bill Barker wrote On 01/19/06 18:11,:
>  
> 
> 
>>-----Original Message-----
>>From: Jan Luehe [mailto:Jan.Luehe@Sun.COM] 
>>Sent: Thursday, January 19, 2006 5:57 PM
>>To: tomcat-dev@jakarta.apache.org
>>Subject: Response not flushed before RD.forward() returns
>>
>>Consider the following code snippet of a servlet's service() method:
>>
>>  public class DispatcherServlet extends HttpServlet {
>>
>>    public void service(HttpServletRequest req, 
>>HttpServletResponse res)
>>        throws IOException, ServletException {
>>
>>      
>>request.getRequestDispatcher("/target").forward(request, response);
>>
>>      try {
>>          Thread.currentThread().sleep(60000);
>>      } catch (Exception ex) { }
>>    }
>>
>>where "target" prints some output to the response.
>>
>>The code currently returns the output printed by "target" only after
>>DispatcherServlet's service() method has finished, instead of right
>>before RD.forward() returns.
>>
>>This seems to be in violation of the Servlet Spec, which has this:
>>
>>SRV.8.4 ("The Forward Method"):
>>
>>  Before the forward() method of the RequestDispatcher interface
>>  returns, the response content must be sent and committed, and closed
>>  by the servlet container.
>>
>>The code at the end of o.a.c.core.ApplicationDispatcher.doForward()
>>looks like this:
>>
>>        // This is not a real close in order to support error 
>>processing
>>        if ( log.isDebugEnabled() )
>>            log.debug(" Disabling the response for futher output");
>>
>>        if  (response instanceof ResponseFacade) {
>>            ((ResponseFacade) response).finish();
>>        } else {
>>            // Servlet SRV.6.2.2. The Resquest/Response may have been
>>wrapped
>>            // and may no longer be instance of RequestFacade
>>            if (log.isDebugEnabled()){
>>                log.debug( " The Response is vehiculed using 
>>a wrapper: "
>>                           + response.getClass().getName() );
>>            }
>>
>>            // Close anyway
>>            try {
>>                PrintWriter writer = response.getWriter();
>>                writer.close();
>>            } catch (IllegalStateException e) {
>>                try {
>>                    ServletOutputStream stream = 
>>response.getOutputStream();
>>                    stream.close();
>>                } catch (IllegalStateException f) {
>>                    ;
>>                } catch (IOException f) {
>>                    ;
>>                }
>>            } catch (IOException e) {
>>                ;
>>            }
>>        }
>>
>>In the above code sample, response will be an instance of
>>ResponseFacade, meaning it will be suspended instead of being flushed
>>and closed right away.
>>
>>Does anyone remember why the "response instanceof ResponseFacade"
>>check is there? I would have expected the "else" case to always be
>>executed.
>>
> 
> 
> Without ever actually having looked at ResponseFacade, I'd always assumed
> that ResponseFacade.finish called Response.finishResponse.  And I would have
> been wrong ;-).  This would have done the commit/send/close properly.
> 
> I don't have time right now to dig through the SVN logs to see why it's this
> way, but suspended doesn't really look good enough to satisfy the spec.

Yes. I'm afraid it's been like this forever.

Does anybody see any problems with removing the
"response instanceof ResponseFacade" check at the end of RD.doForward(),
and unconditionally executing the code in the "else" block, which
commits and closes the response, as requested by the servlet spec?


Jan



> 
>>Any hints appreciated.
>>
>>Thanks,
>>
>>
>>Jan
>>
>>
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