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From Kaleb Pederson <>
Subject Re: Subclassing ServletOutputStream/PrintWriter
Date Tue, 03 Aug 2004 14:34:54 GMT
I probably have the terminology wrong then as this is my first time dealing 
with servlets.  I'm writing an error page that get's called in response to a 
different servlet that we have issuing an error with sendError().  The output 
stream has been written to, but was never sent to the client.  I suppose 
therefore, that it's been written to but not committed?

Thus, I can't use the incoming response object to write to.  As there doesn't 
seem to be a default means of getting at a new outputStream object, or 
printWriter, I presume that I have to subclass ServletOutputStream or 
PrintWriter - correct?

Assuming that's the case, I need to know what functions need to be implemented 
in the two above classes for it to work.  I have actually already extended 
the ServletOutputStream using a very basic class, but it doesn't work in that 
any content written to it, doesn't get pulled into the client browser, even 
after flush is called.  Note that there might be many errors in terms of 
following the specs, as I have yet been able to find any good specs on the 
ServletOutputStream or its interaction with servlets:

import javax.servlet.ServletOutputStream;

public class CustomServletOutputStream extends ServletOutputStream {
    private ByteArrayOutputStream out = null;

    public CustomServletOutputStream() {
        out = new ByteArrayOutputStream();

    public byte[] getBuffer() {
        return out.toByteArray();

    public void write(int data) {

    public void flush() throws IOException {

    public String toString(String enc) throws IOException  {
        return out.toString(enc);

    public String toString() {
        return out.toString();

    public void close() throws IOException {


Thanks for the feedback and help.


On Tuesday 03 August 2004 6:15 am, Shapira, Yoav wrote:
> Hi,
> Why are you doing this at all?  Even if your approach worked you'd be at
> a strange place as far as the Servlet Spec is concerned.  Once a
> response is committed, it should be done.  No more writing.
> Yoav Shapira
> Millennium Research Informatics
> >-----Original Message-----
> >From: Kaleb Pederson []
> >Sent: Monday, August 02, 2004 6:25 PM
> >To: Tomcat Users List
> >Subject: Subclassing ServletOutputStream/PrintWriter
> >
> >I'm receiving a committed response object in an Servlet that I wrote.
> As
> >the
> >response is committed, as far as I can tell, I need to create a custom
> >HttpServletResponseWrapper. But as the response object is committed, it
> >needs
> >to use a new print writer or output stream.  So, as far as I can tell I
> >need
> >to do the following steps:
> >
> >1) Subclass HttpServletResponse wrapper which overrides getWriter() and
> >getOutputStream().
> >2) Subclass PrintWriter (so getWriter will return a non-committed
> object)
> >3) Subclass ServletOutputStream (so getOutputStream will return a
> >non-committed object.)
> >
> >Although I know write(int) needs to be implemented by
> ServletOutputStream,
> >I
> >don't see how that would be nearly sufficient?  How does Tomcat get at
> the
> >buffer associated with an output stream so that it can send it to the
> >client?
> >What should my required steps be?
> >
> >Thanks for the help.
> >
> >--Kaleb
> >
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