Parsing XML string with XPath

Question

Hi,-
I am trying to parse an XML string with xpath as follows but I am getting null for getresult.
I am getting java.xml.xpath.xpathexpressionexception at line where
getresult = xpathexpression.evaluate(isource); is executed.
What should I do after
xpathexpression = xPath.compile("a/b");in the below snippet?
Thanks
String xmlstring ="..."; // a valid XML string;
Xpath xpath = XPathFactory.newInstance().newPath();
xpathexpression = xPath.compile("a/b");
// I guess the following line is not correct
InputSource isource = new inputSource(new ByteArrayInputStream(xmlstring.getBytes())); right
getresult = xpathexpression.evaluate(isource);My xml string is like:
<a>
  <b>
     <result> valid some more tags here
     </result>
  </b>
  <c> 10
  </c>
</a>Edited by: geoman on Dec 8, 2008 2:30 PM

Answer 1

I've never used the version of evaluate that takes an InputSource. The difficulty with using it is that it does not save the DOM object. Each expression you evaluate will have to create the DOM object, use it once and then throw it away. I've yet to write a program that only needs one answer from an XML document. Usually, I use XPath to locate somewhere in a document and then read "nearby" content, add new content nearby, delete content, or move content. I'd suggest you may want to parse the XML stream and save the DOM Document.
Second, all of the XPath expressions search from a "context node". I have not had good luck searching from the Document object, so I always get the root element first. I think the expression should work if you use the root as the context node. You will need one of the versions of evaluate that uses an Object as the parameter.