Java HTML/XML - 如何使用自定义NamespaceContext解析xml

import java.io.FileInputStream;
import java.util.Iterator;

import javax.xml.namespace.NamespaceContext;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Element;
import org.xml.sax.InputSource;

public class Main {
  public static void main(String[] args) throws Exception {
    XPathFactory xpf = XPathFactory.newInstance();
    XPath xp = xpf.newXPath();
    xp.setNamespaceContext(new MyNamespaceContext());
    XPathExpression xpe = xp.compile("ns:feed/ns:entry");
    FileInputStream xmlStream = new FileInputStream("input.xml");
    InputSource xmlInput = new InputSource(xmlStream);
    Element result = (Element) xpe.evaluate(xmlInput, XPathConstants.NODE);
    System.out.println(result);
  }
}
class MyNamespaceContext implements NamespaceContext {
  public String getNamespaceURI(String prefix) {
    if ("ns".equals(prefix)) {
      return "http://www.w3.org/2005/Atom";
    }
    return null;
  }
  public String getPrefix(String namespaceURI) {
    return null;
  }
  public Iterator getPrefixes(String namespaceURI) {
    return null;
  }
}