Question

I’m using XPath to pull out just the values of URL128 XML element. There can be many of these even though I just have one in the below example. When I include xmlns=’http://c1.net.corbis.com/’ on the SearchResponse element I get an empty NodeList, but when I remove that namespace element it works fine. Is there a configuration I’m missing?

String xmlData = "<SearchResponse xmlns='http://c1.net.corbis.com/'><searchResultDataXML><SearchResultData><SearchRequestUID Scope='Public' Type='Guid' Value='{cded773c-c4b7-4dd8-aaee-8e5b8b7a2475}'/><StartPosition Scope='Public' Type='Long' Value='1'/><EndPosition Scope='Public' Type='Long' Value='50'/><TotalHits Scope='Public' Type='Long' Value='323636'/></SearchResultData></searchResultDataXML><imagesXML><Images><Image><ImageUID Scope='Public' Type='Guid' Value='{a6f6d3e2-2c3f-4502-9741-eae2e1bb573a}'/><CorbisID Scope='Public' Type='String' Value='42-25763849'/><Title Scope='Public' Type='String' Value='Animals figurines'/><CreditLine Scope='Public' Type='String' Value='© Ocean/Corbis'/><IsRoyaltyFree Scope='Public' Type='Boolean' Value='True'/><AspectRatio Scope='Public' Type='String' Value='0.666667'/><URL128 Scope='Public' Type='String' Value='http://cachens.corbis.com/CorbisImage/thumb/25/76/38/25763849/42-25763849.jpg'/></Image></Images></imagesXML></SearchResponse>";
            InputSource source = new InputSource(new StringReader(xmlData));

            XPath xPath = XPathFactory.newInstance().newXPath();
            NodeList list = null;
            try {
                list = (NodeList) xPath.evaluate("//URL128/@Value", source, XPathConstants.NODESET);
            } catch (Exception ex) {
                System.out.println(ex.getMessage());
            }
            for (int i = 0; i < list.getLength(); i++) {
                System.out.println(list.item(i).getTextContent());
            }

Answer 1

Well, long story short you need to provide a NamespaceContext to your XPath:

final XPath xPath = XPathFactory.newInstance().newXPath();
xPath.setNamespaceContext(new NamespaceContext() {
    @Override
    public Iterator<String> getPrefixes(final String namespaceURI) {
        return null;
    }
    @Override
    public String getPrefix(final String namespaceURI) {
        return null;
    }
    @Override
    public String getNamespaceURI(final String prefix) {
        return "http://c1.net.corbis.com/";
    }
});
final NodeList list = (NodeList) xPath.evaluate("//c:URL128/@Value", source, XPathConstants.NODESET);
for (int i = 0; i < list.getLength(); i++) {
    System.out.println(list.item(i).getTextContent());
}

It seems the only method XPath requires us to implement in this case is getNamespaceURI(String prefix).

Note that the actual prefix in “c:URL128” doesn’t really matter in this case—you could just as easily use “:URL128”. When you do have multiple namespaces in your XML then it becomes important to distinguish among them (using a Map or a series of if-then-else if relatively few elements).

If you can’t or don’t want to hard code the prefixes you can extract them yourself from the XML document but that requires a little more code…

See also this blog post for more details.