code: public String getParameterString() {
      StringBuilder sb = new StringBuilder(parameters.size() * 10);
      for (Map.Entry<String, Object> entry : parameters.entrySet()) {
        String key = entry.getKey();
        if ("cssClass".equals(key)) key = "class";
        sb.append(" ").append(key).append("=\"").append(entry.getValue().toString()).append("\"");
      }
      return sb.toString();
    }
docs: 将所有额外参数链接起来
  
  @return 空格开始 空格相隔的参数字符串