code: function (protocol) {
        protocol = protocol || 'http';
        return protocol + '://' + publicRuleMethods._str(3, null, ALPHA_LOWER_CASE_CHARS) + '.' + publicRuleMethods._str(5, 15, ALPHA_LOWER_CASE_CHARS) + '.' + publicRuleMethods._str(2, 8, ALPHA_LOWER_CASE_CHARS);
      }
docs: 获取随机 url 地址
  @param {String} [protocol] - url 协议, 默认为 http