xpath search on subtree

Question

I need to restrict the xpath node search to a subtree. I'm currently using the method below but it searches on a whole document regardlest whether I give it the document or the node I want to search from.

private NodeList findNodes(Object obj,String xPathString) throws ... {
    XPath xPath = XPathFactory.newInstance().newXPath();
    XPathExpression expression = xPath.compile(xPathString);
    return (NodeList) expression.evaluate(obj, XPathConstants.NODESET);
}

Solution I'm using now is that I create new document, append the node and search on the new document, then merge. I want to improve this. Can it be done?

The XPath I'm using is //nodeName.

Answer 1

You're looking on the // axis which means 'any descendant node of the document root',

Change it to .// axis (descendands of the context node) and it will work as expected.

Answer 2

You need to distinguish between an absolute and relative XPath expression.

Good question +1.

In XPath, any expression that starts with / is absolute XPath expression. An absolute XPath expression is evaluated on the complete current document.

By contrast, a relative XPath expression is evaluated off the current (context) node.

This explains the reported problem: //nodeName is an absolute XPath expression.

What you want is a relative XPath expression, such as:

.//nodeName

Answer 3

.//nodeName will search for a nodeName element anywhere within the given context node.