XML格式未知时的Java XPath命名空间

Question

I've seen quite a bit of discussion on the topic of Java / XPath, and Namepsaces, but I'm not sure the answers to those questions can help with my particular problem.

I have a program that gets hold of some XML - I don't know the format up-front, but it is likely to contain namespaces. The user can supply an xpath expression that will be used to extract a particular piece of data from the XML. The code is generic - I can't conpile in any namespaces or anything like that as I don't know the format of the XML up-front.

So XML may look like this:

<ns1:item id='myroot' xmlns:ns1='http://www.myplace.com/place'>
    <ns1:category id='cat1'>
        <ns1:item id='item1'>
            <ns1:category id='cat2'></ns1:category>
        </ns1:item>
    </ns1:category>
</ns1:item>

and the xpath that the user enters may be, say:

/ns1:item[@id='myroot']/ns1:category[@id='cat1']

but with the following code, I always get nothing (no matter what XPath I seem to try):

public static String evaluate(String xml, String xpathExpression) throws Exception
{
    String result = "";
    InputSource is = new InputSource(new StringReader(xml));
    XPath xPath = XPathFactory.newInstance().newXPath();
    result = xPath.evaluate(xpathExpression, is);
    System.out.println("result=" +result);
}

Any help greatfully appreciated.

Thanks

Answer 1

Essentially, an expression like

/ns1:item[@id='myroot']/ns1:category[@id='cat1']

is meaningless unless you know what ns1 refers to. So if the user supplies an expression in this form, then they need also to tell you what ns1 means.

XPath 3.0 (at long last) provides a way of defining XPath expressions that don't depend on knowing prefix bindings: you can write

/Q{http://www.myplace.com/place}item[@id='myroot']/Q{http://www.myplace.com/place}category[@id='cat1']

But the only way of achieving this in 1.0 and 2.0 is to write

/*[local-name()='item' and namespace-uri()='http://www.myplace.com/place'][@id='myroot']/*[local-name()='category' and namespace-uri()='http://www.myplace.com/place'][@id='cat1']

Answer 2

The comment from "MadProgrammer" helped me find the answer I was looking for:

String result = "";

DocumentBuilderFactory xmlFactory = DocumentBuilderFactory.newInstance();

xmlFactory.setNamespaceAware(false);

DocumentBuilder builder = xmlFactory.newDocumentBuilder();
InputSource is = new InputSource(new StringReader(xml));
Document document = builder.parse(is);
XPath xPath = XPathFactory.newInstance().newXPath();

result = xPath.evaluate(xpathExpression, document);

return result;

Thanks.