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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 16760] New: - Wrapping response in filter not possible
Date Tue, 04 Feb 2003 15:06:35 GMT
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http://nagoya.apache.org/bugzilla/show_bug.cgi?id=16760

Wrapping response in filter not possible

           Summary: Wrapping response in filter not possible
           Product: Tomcat 4
           Version: 4.1.18
          Platform: PC
        OS/Version: Windows NT/2K
            Status: NEW
          Severity: Blocker
          Priority: Other
         Component: Catalina
        AssignedTo: tomcat-dev@jakarta.apache.org
        ReportedBy: bernd.krannich@gmx.de


The usage of a wrapped response which is derived from 
HttpServletResponseWrapper is no longer possible with Tomcat 4.1.18. In Tomcat 
4.1.12 however, the following coding works fine:

// -- Response wrapper class
class ResponseWrapper extends HttpServletResponseWrapper {
  private PrintWriter printWriter;
  private ReplaceContentOutputStream outputStream;

  public ResponseWrapper(HttpServletResponse response) throws IOException {
    super(response);

    this.outputStream = new ReplaceContentOutputStream(response.getOutputStream
());
    this.printWriter = new PrintWriter(this.outputStream);
  }
    
  public ServletOutputStream getOutputStream() throws IOException {
    return this.outputStream;
  }

  public PrintWriter getWriter() throws IOException {
    return this.printWriter;
  }
}

// -- Wrapped output stream
class ReplaceContentOutputStream extends ServletOutputStream {
  private OutputStream outputStream;
  private ByteArrayOutputStream byteArrayOutputStream;
  private boolean closed = false;
  private boolean transformOnCloseOnly = false;

  public ReplaceContentOutputStream(OutputStream outputStream) {
    this.outputStream = outputStream;
    this.byteArrayOutputStream = new ByteArrayOutputStream();
  }

  public void write(int i) throws IOException {
    this.byteArrayOutputStream.write(i);
  }

  public void close() throws IOException {
    if (!closed) {
      processStream();
      this.outputStream.close();
      closed = true;
    }
  }

  public void flush() throws IOException {
    if (this.byteArrayOutputStream.size() != 0) {
      if (!this.transformOnCloseOnly) {
        processStream();
        this.byteArrayOutputStream = new ByteArrayOutputStream();
      }
    }
  }

  public byte[] replaceContent(byte[] bytes) throws IOException {
    String newString = new String(bytes);
    int replacePosition = newString.indexOf("<%placeholder%>");

    if (replacePosition != -1) {
      newString = newString.substring(0, replacePosition) + "replaced" + 
newString.substring(replacePosition + "<%placeholder%>".length());
    }

    return newString.getBytes();
  }

  public void processStream() throws IOException {
    byte[] bytes = replaceContent(this.byteArrayOutputStream.toByteArray());
    this.outputStream.write(bytes);
  }

  public void setTransformOnCloseOnly() {
    this.transformOnCloseOnly = true;
  }
}

The filter itself is set up to process each request on *.jsp. When the wrapped 
response is passed in to the doFilter method, neither getServletOutputStream() 
nor getWriter() is called (extract from doFilter()):

...
ResponseWrapper wrappedResponse = new ResponseWrapper(this.response);
this.filterChain.doFilter(this.request, wrappedResponse);
wrappedResponse.getOutputStream().close();
...

Thus, the wrapped response itself is entirely empty.

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