Java HTML/XML - 如何从元素获取值

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

import javax.xml.XMLConstants;
import javax.xml.namespace.NamespaceContext;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathFactory;

import org.xml.sax.InputSource;

public class Main {
  public static void main(String[] args) throws Exception {
    String source = "<p xmlns='http://www.w3cschool.cn/nfe' versao='2.00'></p>";

    XPathFactory xPathFactory = XPathFactory.newInstance();
    XPath xPath = xPathFactory.newXPath();

    NamespaceContext context = new NamespaceContext() {
      String PREFIX = "nfe";
      String URI = "http://www.w3cschool.cn/nfe";
      @Override
      public String getNamespaceURI(String prefix) {
        return (PREFIX.equals(prefix)) ? URI : XMLConstants.NULL_NS_URI;
      }
      @Override
      public String getPrefix(String namespaceUri) {
        return (URI.equals(namespaceUri)) ? PREFIX
            : XMLConstants.DEFAULT_NS_PREFIX;
      }
      @Override
      public Iterator getPrefixes(String namespaceUri) {
        return Collections.singletonList(this.getPrefix(namespaceUri))
            .iterator();
      }
    };
    xPath.setNamespaceContext(context);
    InputSource inputSource = new InputSource(new StringReader(source));
    String versao = xPath.evaluate("//nfe:p/@versao", inputSource);
    System.out.println(versao.toString());
  }
}