code: public Map<String, String> getDateFormatMapping() {
          if (null == this.dateFormatMapping) {
              this.dateFormatMapping = new HashMap<String, String>(16);
          }
          return dateFormatMapping;
      }
docs: 获取属性名到日期格式的映射
  
  @return 返回属性名到日期格式的映射