XPathFactory xpf = XPathFactory.newInstance();
XPath xpath = xpf.newXPath();
Map<String, String> namespace = new HashMap<String, String>();
namespace.put("x", "urn:example:po");
DSNamespaceContext context = new DSNamespaceContext(namespace);
xpath.setNamespaceContext(context);
String expression = "//x:Number/text()";
Node ccnumElt =
(Node) xpath.evaluate(expression, doc, XPathConstants.NODE);