急各位大牛帮忙看一个有关问题：java.net.UnknownHostException: www.xxx.com

    public String getHtmlCode(String addr) {        BufferedReader in = null;        URLConnection conn = null;        try {            URL url = new URL("www.xxx.com");            conn = url.openConnection();            conn.setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");            String str;            in = new BufferedReader(new InputStreamReader(conn.getInputStream(), "UTF-8"));            StringBuffer sb = new StringBuffer();            while (null != (str = in.readLine())) {                sb.append(str + "\n");            }            return sb.toString();        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } finally {            try {                if (null != in) in.close();            } catch (IOException e2) {                // TODO: handle exception//            }        }        return null;    }