Header&footer filter (tomcat 4.0-m2)

[ar...@suvi.kas.utu.fi]

Why won't this filter work? Requested page is /test.jsp

-----------------------------------
public void doFilter(ServletRequest request, ServletResponse response)
      throws IOException, ServletException {
         RequestDispatcher 
disp=request.getRequestDispatcher("/header.html");
         disp.include(request, response);
      
         Filter next = filterConfig.getNext();
         next.doFilter(request, response);
      
         disp=request.getRequestDispatcher("/footer.html");
         disp.include(request, response);
      }
-----------------------------------

It throws an exception:

java.lang.IllegalStateException: getOutputStream() has already been called
for this response
	at
org.apache.catalina.connector.ResponseBase.getWriter(ResponseBase.java:636)
	at
javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:133)
	at beans.RespWrapper.getWriter(RespWrapper.java:27)
	at
org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:166)
	at
org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:158)
	at
org.apache.jasper.runtime.JspWriterImpl.flush(JspWriterImpl.java:205)
...

Re: Header&footer filter (tomcat 4.0-m2)

[Arvi Leino <ar...@suvi.kas.utu.fi>]

On Thu, 12 Oct 2000, Craig R. McClanahan wrote:
> It is not allowed to call request.getRequestDispatcher() from within a
> Filter,
> because you are not running inside a servlet at that moment (I will make
> sure this
> clarification gets added to the spec).
>
> - -
> 
> When I get a chance to write one, I will include an example of this sort
> of thing
> in Tomcat.

Thanks! What about setting request attribute for original request, calling
template jsp and template calling original request?

Arvi

Re: Header&footer filter (tomcat 4.0-m2)

["Craig R. McClanahan" <Cr...@eng.sun.com>]

arvleino@suvi.kas.utu.fi wrote:

> Why won't this filter work? Requested page is /test.jsp
>
> -----------------------------------
> public void doFilter(ServletRequest request, ServletResponse response)
>       throws IOException, ServletException {
>          RequestDispatcher
> disp=request.getRequestDispatcher("/header.html");
>          disp.include(request, response);
>
>          Filter next = filterConfig.getNext();
>          next.doFilter(request, response);
>
>          disp=request.getRequestDispatcher("/footer.html");
>          disp.include(request, response);
>       }
> -----------------------------------
>
> It throws an exception:
>
> java.lang.IllegalStateException: getOutputStream() has already been called
> for this response
>         at
> org.apache.catalina.connector.ResponseBase.getWriter(ResponseBase.java:636)
>         at
> javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:133)
>         at beans.RespWrapper.getWriter(RespWrapper.java:27)
>         at
> org.apache.jasper.runtime.JspWriterImpl.initOut(JspWriterImpl.java:166)
>         at
> org.apache.jasper.runtime.JspWriterImpl.flushBuffer(JspWriterImpl.java:158)
>         at
> org.apache.jasper.runtime.JspWriterImpl.flush(JspWriterImpl.java:205)
> ...
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: general-unsubscribe@jakarta.apache.org
> For additional commands, e-mail: general-help@jakarta.apache.org

It is not allowed to call request.getRequestDispatcher() from within a
Filter,
because you are not running inside a servlet at that moment (I will make
sure this
clarification gets added to the spec).

If you want to use a filter to add header/footer text, you will need to
use the
following strategy in your doFilter() method:

* Read the text of your header into an internal buffer (or at
  least count the characters so you know what the ultimate
  content length will be.

* Create a wrapper around the response object you received
  (extends javax.servlet.http.HttpServletResponseWrapper)
  that will be passed on to the rest of the filter chain.

* This wrapper should just buffer up the output created by the
  servlet itself.

* After the servlet returns, figure out how many characters are
  in the footer text as well.

* On the real response object:

    - Set the content length to the sum of the three sizes
      (header text, text returned by the servlet, and footer text)

    - Write all the text (header, servlet, footer) in order

When I get a chance to write one, I will include an example of this sort
of thing
in Tomcat.

Craig McClanahan

====================
See you at ApacheCon Europe <http://www.apachecon.com>!
Session VS01 (23-Oct 13h00-17h00):  Sun Technical Briefing
Session T06  (24-Oct 14h00-15h00):  Migrating Apache JServ
                                    Applications to Tomcat