DOM Document – get or extract contained document (or Node) as XML Source

Something I have to do every once in a while, and can never remember how (especially when under some tight deadline, with people standing over my shoulder asking “is it done yet, is it done?” “how much longer?” etc.) is to extract a fragment of one DOM document to get the XML source of the nested or contained document. So I am going to add a note here, for everyone’s easy reference.

First step is to get a Node to be the Root Node of the new Document. Using methods like Document’s getElementsByTagName(String) and Node.getChildNodes(), or using XPathAPIs and CachedXPathAPI class’ selectSingleNode(Node n, String xPath).

Next we can use a StringWriter and a Transformer to covert the Node to XML Source. Better than a rambling explanation, a simple source example should be do the trick. You can use a method something like the nodeToXMLString example below.

  private String nodeToXMLString(Node node) throws TransformerException
    StringWriter sw = new StringWriter();

    Transformer serializer = TransformerFactory.newInstance().newTransformer();
    serializer.transform(new DOMSource(node), new StreamResult(sw));

    return (sw.toString());