code: private static ChronoUnit create(DateUnit dateUnit) {
          switch (dateUnit) {
              case YEAR:
                  return ChronoUnit.YEARS;
              case MONTH:
                  return ChronoUnit.MONTHS;
              case DAY:
                  return ChronoUnit.DAYS;
              case HOUR:
                  return ChronoUnit.HOURS;
              case MINUTE:
                  return ChronoUnit.MINUTES;
              case SECOND:
                  return ChronoUnit.SECONDS;
              default:
                  throw new DateUtilException("没有单位：" + dateUnit);
          }
      }
docs: 创建相应的ChronoUnit
  
  @param dateUnit 单位
  @return ChronoUnit