* @throws InvalidActivityException
* @throws XPathExpressionException
*/
public String extractValue(String xPathString) throws InvalidActivityException, XPathExpressionException {
if (xmlDocument == null) {
throw new InvalidActivityException("No xml document set to parse.");
}
// Query the xml document by several XPath queries
XPathFactory xPathFactory = XPathFactory.newInstance();
XPath xPath = xPathFactory.newXPath();