TransformerHandler Chaining with Java and Saxon

All,

This is not quite an xsl question, but hopefully someone here has seen
this before and can help me, because I've been banging my head on my
keyboard for hours now. I'm trying to chain together several transforms
using the TransformerHandler chaining design pattern in Java with the
Saxon (8.9) engine. The code below invariable throws an exception
complaining about "The TransformerHandler is not serially reusable. The
startDocument() method must be called once only." when the
reader.parse(source) method is invoked.

Does anyone know why this would be happening and how to prevent it? I am
able to individually transform my file with the transforms by using a
set of rotating temporary files, but I would like to increase the speed
of the transformation (I'm transforming about 17 files comprising 50meg
of data through about 10 transforms and this is taking several minutes)
using chaining if possible.

thanks,
Scott


    private String multiTransform(String sourceFileName, List<String>
transformFiles, String startKey)
    {
        String outFileName = "transformOutput.xml";
        try
        {
            TransformerFactory factory =
TransformerFactory.newInstance();
            SAXTransformerFactory saxTFactory = ((SAXTransformerFactory)
factory);
            List<TransformerHandler> handlers = new
ArrayList<TransformerHandler>();
            TransformerHandler previousHandler = null;
            for (String transformFile : transformFiles)
            {
                StreamSource source = new
StreamSource(Resources.getResource(transformFile).openStream());
                TransformerHandler handler =
saxTFactory.newTransformerHandler(source);
                handlers.add(handler);
                if (previousHandler != null)
                {
                    previousHandler.setResult(new SAXResult(handler));
                    break;
                }
                previousHandler = handler;
            }

            XMLReader reader = XMLReaderFactory.createXMLReader();
            reader.setContentHandler(handlers.get(0));

            TransformerHandler lastHandler =
handlers.get(handlers.size() - 1);
            OutputStream resultOutStream = new
FileOutputStream(outFileName);
            StreamResult xformOutResult = new
StreamResult(resultOutStream);
            lastHandler.setResult(xformOutResult);
            FileInputStream fileInStrm = new
FileInputStream(sourceFileName);
            InputSource source = new InputSource(fileInStrm);
            reader.parse(source);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        return outFileName;
    }



The exception...

java.lang.UnsupportedOperationException: The TransformerHandler is not
serially reusable. The startDocument() method must be called once only.
	at
net.sf.saxon.TransformerHandlerImpl.startDocument(TransformerHandlerImpl
.java:69)
	at
net.sf.saxon.event.ContentHandlerProxy.open(ContentHandlerProxy.java:242
)
	at net.sf.saxon.event.ProxyReceiver.open(ProxyReceiver.java:76)
	at
net.sf.saxon.event.ImplicitResultChecker.open(ImplicitResultChecker.java
:24)
	at
net.sf.saxon.event.ImplicitResultChecker.firstContent(ImplicitResultChec
ker.java:59)
	at
net.sf.saxon.event.ImplicitResultChecker.startElement(ImplicitResultChec
ker.java:30)
	at
net.sf.saxon.event.NamespaceReducer.startElement(NamespaceReducer.java:5
4)
	at
net.sf.saxon.event.ComplexContentOutputter.startContent(ComplexContentOu
tputter.java:481)
	at
net.sf.saxon.event.ComplexContentOutputter.characters(ComplexContentOutp
utter.java:136)
	at net.sf.saxon.instruct.Copy.processLeavingTail(Copy.java:164)
	at
net.sf.saxon.instruct.Choose.processLeavingTail(Choose.java:338)
	at
net.sf.saxon.instruct.Template.applyLeavingTail(Template.java:99)
	at
net.sf.saxon.instruct.ApplyTemplates.applyTemplates(ApplyTemplates.java:
319)
	at
net.sf.saxon.instruct.ApplyTemplates.apply(ApplyTemplates.java:189)
	at
net.sf.saxon.instruct.ApplyTemplates.process(ApplyTemplates.java:149)
	at
net.sf.saxon.instruct.ElementCreator.processLeavingTail(ElementCreator.j
ava:250)
	at net.sf.saxon.instruct.Copy.processLeavingTail(Copy.java:152)
	at
net.sf.saxon.instruct.Choose.processLeavingTail(Choose.java:338)
	at
net.sf.saxon.instruct.Template.applyLeavingTail(Template.java:99)
	at
net.sf.saxon.instruct.ApplyTemplates.applyTemplates(ApplyTemplates.java:
319)
	at
net.sf.saxon.instruct.ApplyTemplates.defaultAction(ApplyTemplates.java:3
51)
	at
net.sf.saxon.instruct.ApplyTemplates.applyTemplates(ApplyTemplates.java:
312)
	at
net.sf.saxon.Controller.transformDocument(Controller.java:1602)
	at
net.sf.saxon.TransformerHandlerImpl.endDocument(TransformerHandlerImpl.j
ava:133)
	at
com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endDocument
(AbstractSAXParser.java:737)
	at
com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.s
canDocument(XMLDocumentFragmentScannerImpl.java:515)
	at
com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML1
1Configuration.java:807)
	at
com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML1
1Configuration.java:737)
	at
com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.jav
a:107)
	at
com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(Abstr
actSAXParser.java:1205)