哪位高手有截取url中 一级域名的 java代码

String s = "topic.****.net/u/20120604/22/2479ec15-887a-4a7f-9ca6-042d37214302.html";
Pattern p = Pattern.compile("(?<=//|)((\\w)+\\.)+\\w+");
Matcher m = p.matcher(s);
if(m.find()){
      System.out.println(m.group());
}