Java – why can only some XPath expressions find nodes when XML has a namespace prefix

In the following example code, any XPath of the form '/ / elementname' will return null when the source XML has a namespace prefix (see testwithns()) in the bottom code)

When the source XML does not have a namespace prefix, all listed XPath expressions return a node (see testnos())

I know I can solve this problem by setting the namespacecontext (as in testwithnscontext()), parsing XML into namespace aware documents, and using namespace prefixes in XPath But I don't want to, because my actual code needs to deal with XML with and without namespace prefixes

My question is why it just:

>/ / test > / / Child1 > / / Child1 > / / child2

Returns null, but all other examples in testwithns() return nodes?

yield

testNoNS()
test = found
/test = found
//test = found
//test/* = found
//test/child1 = found
//test/child1/grandchild1 = found
//test/child2 = found
//child1 = found
//grandchild1 = found
//child1/grandchild1 = found
//child2 = found

testWithNS()
test = found
/test = found
//test = *** NOT FOUND ***
//test/* = found
//test/child1 = found
//test/child1/grandchild1 = found
//test/child2 = found
//child1 = *** NOT FOUND ***
//grandchild1 = *** NOT FOUND ***
//child1/grandchild1 = found
//child2 = *** NOT FOUND ***

testWithNSContext()
ns1:test = found
/ns1:test = found
//ns1:test = found
//ns1:test/* = found
//ns1:test/ns1:child1 = found
//ns1:test/ns1:child1/ns1:grandchild1 = found
//ns1:test/ns1:child2 = found
//ns1:child1 = found
//ns1:grandchild1 = found
//ns1:child1/ns1:grandchild1 = found
//ns1:child2 = found

code

import java.io.StringReader;
import java.util.Iterator;

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

import org.junit.Test;
import org.w3c.dom.Document;
import org.xml.sax.InputSource;

public class XPathBugTest {

    private String xmlDec = "<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"yes\"?>";
    private String xml = xmlDec + 
        "<test>" +
        "  <child1>" +
        "    <grandchild1/>" +
        "  </child1>" +
        "  <child2/>" +
        "</test>";
    private String xmlNs = xmlDec + 
        "<ns1:test xmlns:ns1=\"http://www.wfmc.org/2002/XPDL1.0\">" +
        "  <ns1:child1>" +
        "    <ns1:grandchild1/>" +
        "  </ns1:child1>" +
        "  <ns1:child2/>" +
        "</ns1:test>";

    final XPathFactory xpathFactory = XPathFactory.newInstance();
    final XPath xpath = xpathFactory.newXPath();

    @Test
    public void testNoNS() throws Exception {
        System.out.println("\ntestNoNS()");
        final Document doc = getDocument(xml);

        isFound("test",xpath.evaluate("test",doc,XPathConstants.NODE));
        isFound("/test",xpath.evaluate("/test",XPathConstants.NODE));
        isFound("//test",xpath.evaluate("//test",XPathConstants.NODE));
        isFound("//test/*",xpath.evaluate("//test/*",XPathConstants.NODE));
        isFound("//test/child1",xpath.evaluate("//test/child1",XPathConstants.NODE));
        isFound("//test/child1/grandchild1",xpath.evaluate("//test/child1/grandchild1",XPathConstants.NODE));
        isFound("//test/child2",xpath.evaluate("//test/child2",XPathConstants.NODE));
        isFound("//child1",xpath.evaluate("//child1",XPathConstants.NODE));
        isFound("//grandchild1",xpath.evaluate("//grandchild1",XPathConstants.NODE));
        isFound("//child1/grandchild1",xpath.evaluate("//child1/grandchild1",XPathConstants.NODE));
        isFound("//child2",xpath.evaluate("//child2",XPathConstants.NODE));
    }

    @Test
    public void testWithNS() throws Exception {
        System.out.println("\ntestWithNS()");
        final Document doc = getDocument(xmlNs);

        isFound("test",XPathConstants.NODE));
    }

    @Test
    public void testWithNSContext() throws Exception {
        System.out.println("\ntestWithNSContext()");
        final Document doc = getDocumentNS(xmlNs);

        xpath.setNamespaceContext(new MyNamespaceContext());

        isFound("ns1:test",xpath.evaluate("ns1:test",XPathConstants.NODE));
        isFound("/ns1:test",xpath.evaluate("/ns1:test",XPathConstants.NODE));
        isFound("//ns1:test",xpath.evaluate("//ns1:test",XPathConstants.NODE));
        isFound("//ns1:test/*",xpath.evaluate("//ns1:test/*",XPathConstants.NODE));
        isFound("//ns1:test/ns1:child1",xpath.evaluate("//ns1:test/ns1:child1",XPathConstants.NODE));
        isFound("//ns1:test/ns1:child1/ns1:grandchild1",xpath.evaluate("//ns1:test/ns1:child1/ns1:grandchild1",XPathConstants.NODE));
        isFound("//ns1:test/ns1:child2",xpath.evaluate("//ns1:test/ns1:child2",XPathConstants.NODE));
        isFound("//ns1:child1",xpath.evaluate("//ns1:child1",XPathConstants.NODE));
        isFound("//ns1:grandchild1",xpath.evaluate("//ns1:grandchild1",XPathConstants.NODE));
        isFound("//ns1:child1/ns1:grandchild1",xpath.evaluate("//ns1:child1/ns1:grandchild1",XPathConstants.NODE));
        isFound("//ns1:child2",xpath.evaluate("//ns1:child2",XPathConstants.NODE));
    }

    private void isFound(String xpath,Object object) {
        System.out.println(xpath + " = " + (object == null ? "*** NOT FOUND ***" : "found"));
    }

    private Document getDocument(final String xml) throws Exception {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        return factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));        
    }

    private Document getDocumentNS(final String xml) throws Exception {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
        return factory.newDocumentBuilder().parse(new InputSource(new StringReader(xml)));
    }

    public class MyNamespaceContext implements NamespaceContext {
        @Override
        public String getNamespaceURI(String prefix) {
            if ("ns1".equals(prefix)) {
                return "http://www.wfmc.org/2002/XPDL1.0";
            }
            return XMLConstants.NULL_NS_URI;
        }
        @Override
        public String getPrefix(String uri) {
            throw new UnsupportedOperationException();
        }
        @Override
        public Iterator getPrefixes(String uri) {
            throw new UnsupportedOperationException();
        }
    }
}

Update after Saxon test

I now use Saxon to change the xpahtfactory line to test the same code

final XPathFactory xpathFactory = new net.sf.saxon.xpath.XPathFactoryImpl();

Use all lines in Saxon testwithns() to return * * * not found * * * instead of returning the default xalan implementation like '/ / elementname'

Given that I'm using a non namespace aware document builder factory to parse XML, why don't these xpaths work and only some use xalan?

Solution

If you want to ignore namespaces, you can use the local name XPath function:

//*[local-name()='grandchild1']