java - Linux 上的 UnknownHostExcetpion

Question

我在方法中收到 UnknownHostException: www.google.com

public static String getSource(String url) throws IOException {
    URL u = new URL(url);
    URLConnection conn = u.openConnection();
    conn.setRequestProperty("User-Agent",
            "Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.4;"
                    + " en-US; rv:1.9.2.2) "
                    + "Gecko/20100316 Firefox/3.6.2");
    BufferedReader in = new BufferedReader(new InputStreamReader(
            conn.getInputStream(), "UTF-8"));
    String inputLine;
    StringBuilder a = new StringBuilder();
    while ((inputLine = in.readLine()) != null) {
        a.append(inputLine);
    }
    in.close();
    return a.toString();
}

我在 Ubuntu 13.10 上遇到了这个问题，但在 Windows 7 上一切正常。