java正则表达式获取url的host示例

public static string gethost(string url){
  if(url==null||url.trim().equals("")){
   return "";
  }
  string host = "";
  pattern p =  pattern.compile("(?<=//|)((\\w)+\\.)+\\w+");
  matcher matcher = p.matcher(url); 
  if(matcher.find()){
   host = matcher.group(); 
  }
  return host;
 }