code: private NodeList getNodeList(String document, XPathExpression expression) throws Exception
     {
        Document doc = m_documentBuilder.parse(new InputSource(new StringReader(document)));
        return (NodeList) expression.evaluate(doc, XPathConstants.NODESET);
     }
docs: Retrieve a node list based on an XPath expression.
  
  @param document XML document to process
  @param expression compiled XPath expression
  @return node list