计算两个时间之间相差几天、月、年

ChronoUnit类

//获取当前时间（2021-06-22）
        LocalDate today = LocalDate.now();
        //将String转LocalDateTime
        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDate collectTimeDate = LocalDate.parse("2021-05-01",df);
        //判断相差多少天
        log.info("ChronoUnit====相差{}年，相差{}月，相差{}天",
                ChronoUnit.YEARS.between(collectTimeDate,today),
                ChronoUnit.MONTHS.between(collectTimeDate,today),
                ChronoUnit.DAYS.between(collectTimeDate,today));

注意：若调用获取时、分、秒、半天方法皆报错

结果：

//获取当前时间(2021-06-22 17:27:03)
        LocalDateTime today = LocalDateTime.now();
        //将String转LocalDateTime
        DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime collectTimeDate = LocalDateTime.parse("2021-05-01 16:40:23",df);
        //判断相差多少天
        log.info("ChronoUnit====相差{}年，相差{}月，相差{}天",
                ChronoUnit.YEARS.between(collectTimeDate,today),
                ChronoUnit.MONTHS.between(collectTimeDate,today),
                ChronoUnit.DAYS.between(collectTimeDate,today));
        
        log.info("ChronoUnit====相差{}小时，相差{}分钟，相差{}秒",
                ChronoUnit.HOURS.between(collectTimeDate,today),
                ChronoUnit.MINUTES.between(collectTimeDate,today),
                ChronoUnit.SECONDS.between(collectTimeDate,today));
        
        log.info("ChronoUnit====相差{}半天",ChronoUnit.HALF_DAYS.between(collectTimeDate,today));

结果：

Period类

//获取当前时间(2021-06-22)
        LocalDate todayDate = LocalDate.now();
        //将String转LocalDateTime
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDate lastDate = LocalDate.parse("2021-05-01",dtf);
        //判断相差多少天
        log.info("Period====相差{}年，相差{}月，相差{}天",
                Period.between(lastDate,todayDate).getYears(),
                Period.between(lastDate,todayDate).getMonths(),
                Period.between(lastDate,todayDate).getDays());

注意：Period.between方法只接收LocalDate类型的传参

结果：

从结果中可看到，两个时间本是相差52天，但此处只显示相差21天；因为此处只用两者的日相减，不管年份和月份

Duration类

//获取当前时间(2021-06-22 17:27:03)
        LocalDateTime currentDate = LocalDateTime.now();
        //将String转LocalDateTime
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        LocalDateTime date = LocalDateTime.parse("2021-05-01 16:40:23",formatter);

        log.info("Duration====相差{}天，相差{}小时，相差{}分钟",
                Duration.between(date,currentDate).toDays(),
                Duration.between(date,currentDate).toHours(),
                Duration.between(date,currentDate).toMinutes());

结果：

以下这种会报错：

//获取当前时间(2021-06-22)
        LocalDate currentDate = LocalDate.now();
        //将String转LocalDate
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
        LocalDate date = LocalDate.parse("2021-05-01",formatter);
        //判断相差多少天
        log.info("Duration====相差{}天", Duration.between(date,currentDate).toDays());

结果：

综上，推荐使用ChronoUnit类