名前空間ありの XML で XPath

名前空間ありの XML で XPath するときは javax.xml.namespace.NamespaceContext を実装する必要がある。めんどっ。

package tmp;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Arrays;
import java.util.Iterator;

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

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

public class NSTest {
  public static Document getDocument(String url) throws IOException, SAXException, ParserConfigurationException {
    HttpURLConnection connection = null;
    BufferedInputStream in = null;

    try {
      connection = (HttpURLConnection) new URL(url).openConnection();
      connection.setRequestMethod("GET");
      in = new BufferedInputStream(connection.getInputStream());
      DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
      factory.setNamespaceAware(true);
      return factory.newDocumentBuilder().parse(in);

    } finally {
      if (in != null) {
        try {
          in.close();
        } catch (IOException e) {
          // do nothing
        }
      }
      if (connection != null) {
        connection.disconnect();
      }
    }
  }

  public static void main(String[] args) throws Exception {
    XPath xpath = XPathFactory.newInstance().newXPath();
    xpath.setNamespaceContext(new NamespaceContext() {
      public String getNamespaceURI(String prefix) {
        if (prefix == null)
          throw new IllegalArgumentException();
        else if ("hatena".equals(prefix))
          return "http://www.hatena.ne.jp/info/xmlns#";
        return null;
      }

      public String getPrefix(String namespaceURI) {
        if (namespaceURI == null)
          throw new IllegalArgumentException();
        else if ("http://www.hatena.ne.jp/info/xmlns#".equals(namespaceURI))
          return "hatena";
        return null;
      }

      public Iterator<String> getPrefixes(String namespaceURI) {
        if (namespaceURI == null)
          throw new IllegalArgumentException();
        else if ("http://www.hatena.ne.jp/info/xmlns#".equals(namespaceURI))
          return Arrays.asList("hatena").iterator();
        return null;
      }
    });

    Document document = NSTest.getDocument("http://f.hatena.ne.jp/twitter/rss");
    NodeList nodes = (NodeList) xpath.evaluate("//hatena:imageurl", document, XPathConstants.NODESET);
    for (int i = 0, m = nodes.getLength(); i < m; ++i) {
      System.out.println(nodes.item(i).getTextContent());
    }
  }
}

d:\tmp> java tmp.NSTest
http://f.hatena.ne.jp/images/fotolife/t/twitter/20080413/20080413235100.jpg
http://f.hatena.ne.jp/images/fotolife/t/twitter/20080413/20080413235054.jpg
http://f.hatena.ne.jp/images/fotolife/t/twitter/20080413/20080413234330.jpg
...