Strange Java XPath Recognizer Behavior for Documents with Namespaces

Question

I need to query XML documents using XPath expressions in a Java application. I created the following class that accepts a file (the location of the XML document on the local hard drive) and the XPath request and should return the result of evaluating this request in this document.

import java.io.File;
import java.io.IOException;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathException;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.SAXException;

public class XPathResolver 
{
    public String resolveXPath(File xmlFile, String xpathExpr) throws XPathException, ParserConfigurationException, SAXException, IOException
    {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();
        Document doc = builder.parse(xmlFile);

        XPathFactory xPathfactory = XPathFactory.newInstance();
        XPath xpath = xPathfactory.newXPath();

        XPathExpression expr = xpath.compile(xpathExpr);

        return (String) expr.evaluate(doc, XPathConstants.STRING);
    }
}

Suppose now that I have the following XML document.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Document>
    <DocumentFormat>Email</DocumentFormat>
    <FileFormat>PDF</FileFormat>
</Document>

Evaluation of both /Document/FileFormat, and //FileFormatreturn PDF(as expected).

Suppose now that a document with namespace prefixes, for example, is as follows.

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Document xmlns:file="http://www.example.com/xml/file">
    <DocumentFormat>Email</DocumentFormat>
    <file:FileFormat>PDF</file:FileFormat>
</Document>

Now /Document/FileFormatreturns PDF, but //FileFormatreturns nothing.

Why does my code not return the expected result in the case of documents with namespace prefixes and how to fix it?

Answer 1

JDK 1.7.0.51 . , DocumentBuilderFactory - .

, :

factory.setNamespaceAware(true);

XPath, .

: /Document/file:FileFormat //file:FileFormat. NamespaceContext, , XPath, URI . , .

public String resolveXPath(File xmlFile, String xpathExpr) throws XPathException, ParserConfigurationException, SAXException, IOException, XPathExpressionException
{
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

    // Turn namespace aware on
    factory.setNamespaceAware(true);
    DocumentBuilder builder = factory.newDocumentBuilder();
    Document doc = builder.parse(xmlFile);

    XPathFactory xPathfactory = XPathFactory.newInstance();
    XPath xpath = xPathfactory.newXPath();

    // Set the NamespaceContext        
    xpath.setNamespaceContext(new MyNamespaceContext());


    XPathExpression expr = xpath.compile(xpathExpr);

    return (String) expr.evaluate(doc, XPathConstants.STRING);
}

class MyNamespaceContext implements NamespaceContext {

  private Map<String, String> ns;
  private Map<String, String> nsReverted;

  public MyNamespaceContext() {
    ns = new TreeMap<String, String>();

    // Default namespaces and prefixes according to the documentation
    ns.put(XMLConstants.DEFAULT_NS_PREFIX, XMLConstants.NULL_NS_URI);
    ns.put(XMLConstants.XML_NS_PREFIX, XMLConstants.XML_NS_URI);
    ns.put(XMLConstants.XMLNS_ATTRIBUTE, XMLConstants.XMLNS_ATTRIBUTE_NS_URI);

    // Now our self defined namespace
    ns.put("file", "http://www.example.com/xml/file");


    nsReverted = new TreeMap<String, String>();
    for(Entry<String, String> entry : ns.entrySet()) {
      nsReverted.put(entry.getValue(), entry.getValue());
    }
  }

  @Override
  public String getNamespaceURI(String prefix) {
    if(prefix == null) {
      throw new IllegalArgumentException();
    } 
    final String uri = ns.get(prefix);
    return uri == null ? XMLConstants.NULL_NS_URI : uri;
  }

  @Override
  public String getPrefix(String namespaceURI) {
    if(namespaceURI == null) {
      throw new IllegalArgumentException();
    } 
    return nsReverted.get(namespaceURI);
  }

  @Override
  public Iterator getPrefixes(String namespaceURI) {
    return ns.keySet().iterator();
  }

}

Answer 2

"Now/Document/FileFormat PDF" - , , .

, XPath, XPath, , XPath, , kluge , -uri.

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