private ByteArrayOutputStream pdf()
{
  // binary container for PDF
  ByteArrayOutputStream out = null;

  try
  {
    // assume these exist
    String xsl, xml;

    TransformerFactory transformerFactory = TransformerFactory.newInstance();

    // configure FOP, apache's XML->PDF transformer
    Fop fop = new Fop(MimeConstants.MIME_PDF);
    out = new ByteArrayOutputStream();
    fop.setOutputStream(out);

    // configure XSLT transformer
    Source xsltSrc = new StreamSource(new StringReader(xsl));
    Transformer transformer = transformerFactory.newTransformer(xsltSrc);

    // pipe XSL transformation through to FOP
    Result res = new SAXResult(fop.getDefaultHandler());

    // grab XML input stream
    Source src = new StreamSource(new StringReader(xml));

    // Start the transformation and rendering process
    transformer.transform(src, res);
  }
  catch (Exception e)
  {
    // actually, catch the following, one by one:
    // TransformerConfigurationException
    // FOPException
    // TransformerFactoryConfigurationError
    // TransformerException
  }

  return out;
}

public void appendToResponse(WOResponse response, WOContext context)
{
  ByteArrayOutputStream out = pdf();

  // without data, show the PDF page, which is just an error message.
  if (out == null)
    super.appendToResponse(response, context);

  // assume this exists
  String filename;

  response.setHeader("application/pdf", "Content-Type");
  response.setHeader("" + out.size() + "", "Content-Length");
  response.setHeader("attachment;filename=" + filename, "Content-Disposition");
  response.setContent(new NSData(out.toByteArray()));
}