xslt servlet that uses foo.xml and rewrites foo.xml

Hi,

I am trying to write a servlet that takes an XML file transforms that file
and rewrites it.  When I try the code below I get a malformed document
exception (no root element) because the document (Result I assume) is
prepared for writing??? by having everything deleted form it.

How can I write a simple servlet that rewrites the source document? How can
I get the the StreamSource into a variable so I can transform it back into
the original file?
Note: if I write out to a new file there is no problem with the
transformation.
-----------------------------------
public class AddPage extends HttpServlet {

   public void doPost(HttpServletRequest req, HttpServletResponse res)
                        throws ServletException, IOException {

      res.setContentType("text/plain");
      PrintWriter out = res.getWriter();

      String xmlref = "c:/resin/doc/ed/xml/config.xml";
      String xslref = "c:/resin/doc/ed/xml/addpage.xsl";
      String parentElem = req.getParameter("parentElem");

      try {
         TransformerFactory tFactory = TransformerFactory.newInstance();
         Transformer transformer = tFactory.newTransformer(new
StreamSource(xslref));
         transformer.setParameter("id",parentElem);
         StreamSource strmsrc = new StreamSource(xmlref);
         //StreamResult strmrslt = new StreamResult(xmlref);
         transformer.transform (strmsrc, new StreamResult(xmlref));
      }
       catch (Exception e) {
         out.write(e.getMessage());
         e.printStackTrace(out);
       }
       out.close();
}
---------------------------
Thanks,
Rob


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