Question

I have the following code:

// xpath evaluates to net.sf.saxon.xpath.XPathEvaluator
XPath xpath = XPathFactory.newInstance().newXPath(); 
XPathExpression expression = xpath.compile("/foo/bar");
Object evaluate = expression.evaluate(someXML, XPathConstants.NODE);
Object evaluate2 = expression.evaluate(someXML, XPathConstants.NODESET);

System.out.println(evaluate!=null?evaluate.getClass():"null");
System.out.println(evaluate2!=null?evaluate2.getClass():"null2");

System.out.println(evaluate instanceof Node);
System.out.println(evaluate2 instanceof NodeList);

and this is the result…

class net.sf.saxon.tinytree.TinyElementImpl
class java.util.ArrayList
false
false

Just to clarify, if I do this:

org.w3c.dom.Node node = (org.w3c.dom.Node)evaluate;

or

org.w3c.dom.NodeList node = (org.w3c.dom.NodeList)evaluate2;

I get a ClassCastException

How can that be? according to Suns Java 1.5 API NODE and NODESET should map to org.w3c.dom.Node and org.w3c.dom.NodeList respectively

Just to clarify2 yes I know Node is an iterface, that getClass() returns a concrete class.

Answer 1

Ok I figured it out!

If the evaluate method receives an InputSource the above error occurs.

e.g.

InputSource someXML = new InputSource(new StringReader("<someXML>...</someXML>)");
Object result = expression.evaluate(someXML, XPathConstants.NODE); 
Node node = (Node) result; // ClassCastException

Then result is not implementing org.w3c.dom.Node (TinyElementImpl)

But if evaluate receives a Node (or a Document):

DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder documentBuilder = builderFactory.newDocumentBuilder();
Document someXML = documentBuilder.parse(new InputSource(new StringReader("<someXML>...</someXML>)"));
Object result = expression.evaluate(someXML, XPathConstants.NODE);
Node node = (Node) result; // works

It works, but still, this is weird…