XPath: Is there a way to set a default namespace for queries?

Is there a wa开发者_JS百科y to set Java's XPath to have a default namespace prefix for expressons? For example, instead of: /html:html/html:head/html:title/text()", the query could be: /html/head/title/text()

While using the namespace prefix works, there has to be a more elegant way.

Sample code snippet of what I'm doing now:

Node node = ... // DOM of a HTML document
XPath xpath = XPathFactory.newInstance().newXPath();

// set to a NamespaceContext that simply returns the prefix "html"
// and namespace URI ""http://www.w3.org/1999/xhtml"
xpath.setNamespaceContext(new HTMLNameSpace());

String expression = "/html:html/html:head/html:title/text()";
String value = xpath.evaluate(query, expression);

Unfortunately, no. There was some talk about defining a default namespace for JxPath a few years ago, but a quick look at the latest docs don't indicate that anything happened. You might want to spends some more time looking through the docs, though.

One thing that you could do, if you really don't care about namespaces, is to parse the document without them. Simply omit the call that you're currently making to DocumentBuilderFactory.setNamespaceAware().

Also, note that your prefix can be anything you want; it doesn't have to match the prefix in the instance document. So you could use h rather than html, and minimize the visual clutter of the prefix.

I haven't actually tried this, but according to the NamespaceContext documentation, the namespace context with the prefix "" (emtpy string) is considered to be the default namespace.

I was a little bit too quick on that one. The XPath evaluator does not invoke the NamespaceContext to resolve the "" prefix, if no prefix is used at all in the XPath expression "/html/head/title/text()". I'm now going into XML details, which I am not 100% sure about, but using an expression like "/:html/:head/:title/text()" works with Sun JDK 1.6.0_16 and the NamespaceContext is asked to resolve an empty prefix (""). Is this really correct and expected behaviour or a bug in Xalan?

I know this question is old but I just spent 3 hours researching trying to solve this problem and @kdgregorys answer helped me out alot. I just wanted to put exactly what I did using kdgregorys answer as a guide.

The problem is that XPath in java doesnt even look for a namespace if you dont have a prefix on your query therefore to map a query to a specific namespace you have to add a prefix to the query. I used an arbitrary prefix to map to the schema name. For this example I will use OP's namespace and query and the prefix abc. Your new expression would look like this:

String expression = "/abc:html/abc:head/abc:title/text()";

Then do the following

1) Make sure your document is set to namespace aware.

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);

2) Implement a NamespaceContext that will resolve your prefix. This one I took from some other post on SO and modified a bit

.

public class NamespaceResolver implements NamespaceContext {

    private final Document document;

    public NamespaceResolver(Document document) {
        this.document = document;
    }

    public String getNamespaceURI(String prefix) {
        if(prefix.equals("abc")) {
            // here is where you set your namespace
            return "http://www.w3.org/1999/xhtml";
        } else if (prefix.equals(XMLConstants.DEFAULT_NS_PREFIX)) {
            return document.lookupNamespaceURI(null);
        } else {
            return document.lookupNamespaceURI(prefix);
        }
    }

    public String getPrefix(String namespaceURI) {
        return document.lookupPrefix(namespaceURI);
    }

    @SuppressWarnings("rawtypes")
    public Iterator getPrefixes(String namespaceURI) {
        // not implemented
        return null;
    }

}

3) When creating your XPath object set your NamespaceContext.

xPath.setNamespaceContext(new NamespaceResolver(document));

Now no matter what the actual schema prefix is you can use your own prefix that will map to the proper schema. So your full code using the class above would look something like this.

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);

Document document = factory.newDocumentBuilder().parse(sourceDocFile);

XPathFactory xPFactory = XPathFactory.newInstance();
XPath xPath = xPFactory.newXPath();
xPath.setNamespaceContext(new NamespaceResolver(document));

String expression = "/abc:html/abc:head/abc:title/text()";
String value = xpath.evaluate(query, expression);