* @return list of attribute values.
* @throws XPathExpressionException
*/
private static List<String> xpathGetAttributeValueList(Document doc, String expression, String attribute) throws XPathExpressionException {
XPathFactory xPathFactory = XPathFactory.newInstance();
XPath xPath = xPathFactory.newXPath();
XPathExpression expr = xPath.compile(expression);
NodeList nl = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
List<String> attributeValues = new ArrayList<String>();