DOM dropping needed namespace attribute

Question

So I have the XML document:
<?xml version="1.0" encoding="UTF-8"?>
<ClinicalDocument xmlns="urn:hl7-org:v3"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
classCode="DOCCLIN" moodCode="EVN" />I pass it to the following:
private void xmlTweak(String location) {
    try {               
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder db = factory.newDocumentBuilder();
        org.w3c.dom.Document doc = db.parse(new File(location));
        TransformerFactory tFactory = TransformerFactory.newInstance();
        Transformer transformer = tFactory.newTransformer();
        DOMSource source = new DOMSource(doc);
        FileOutputStream fos = new FileOutputStream(location);
        transformer.transform(source, new StreamResult(fos));
    catch(Exception e) {
        e.printStackTrace();
}All that the above code should be doing is reading it in and outputting the same thing, but it gives me:
<?xml version="1.0" encoding="UTF-8"?>
<ClinicalDocument
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
classCode="DOCCLIN" moodCode="EVN"/>Notice that the xmlns namespace attribute is missing; I need that attribute in order to get it to pass a schema. After I read the XML file in, if I try doc.getDocumentElement().getAttribute("xmlns"), it confirms that xmlns="urn:hl7-org:v3". I suppose the problem occurs when outputting it back to a file, but what could that problem be?

Answer 1

I found the problem. In case anyone is interested, the problem was with the TransformerFactory. I was using a saxon 8 TransformerFactory, which unexpectedly removed the attribute. Using com.sun.org.apache.xalan.internal.xsltc.trax.TransformerFactoryImpl instead works, so I've switched to it.