Date与LocalDateTime、LocalDate、LocalTime互转，以及LocalDateTime常规操作

一、Date与LocalDateTime、LocalDate、LocalTime互转

1、Date转LocalDateTime、LocalDate、LocalTime

LocalDate localDate = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
LocalTime localTime = date.toInstant().atZone(ZoneId.systemDefault()).toLocalTime();
LocalDateTime localDateTime = date.toInstant().atZone(ZoneId.systemDefault()).toLocalDateTime()；

上面很容易看出，无论是date转哪个，都是首先date.toInstant().atZone(ZoneId.systemDefault())，然后是相应的toLocalDate()、toLocalTime()、toLocalDateTime()

2、LocalDateTime、LocalDate、LocalTime转Date

Date date1 = Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
Date date2 = Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
Date date3 = Date.from(localTime.atDate(LocalDate.now()).atZone(ZoneId.systemDefault()).toInstant());

上面可以看出，

• LocalDateTime可以直接转：Date.from(localDateTime.atZone(ZoneId.systemDefault()).toInstant());
• LocalDate需要先调用atStartOfDay()设置默认时间，然后再转：Date.from(localDate.atStartOfDay(ZoneId.systemDefault()).toInstant());
• LocalTime需要先设置日期转成LocalDateTime再转：Date.from(localTime.atDate(LocalDate.now()).atZone(ZoneId.systemDefault()).toInstant());

二、LocalDateTime的常规操作

1、LocalDateTime 初始化定义

LocalDateTime now = LocalDateTime.now();
LocalDateTime localDateTime=LocalDateTime.of(LocalDate.now(),LocalTime.now());//LocalDate和LocalTime合成LocalDateTime
LocalDateTime of = LocalDateTime.of(2020, 11, 11, 20, 30, 40);

2、LocalDateTime 日期加减

LocalDateTime localDateTime = LocalDateTime.of(2020, 11, 11, 11, 11, 59);//2020-11-11 11:11:59
LocalDateTime localDateTime1 = localDateTime.plusSeconds(1);//2020-11-11 11:11:59 +1秒，localDateTime1=2020-11-11 11:12:00
LocalDateTime localDateTime2 = localDateTime.plusSeconds(-1);//2020-11-11 11:11:59 -1秒，localDateTime2=2020-11-11 11:11:58
LocalDateTime localDateTime3 = localDateTime.plusMinutes(1);//2020-11-11 11:11:59 +1分钟，localDateTime3=2020-11-11 11:12:59
LocalDateTime localDateTime4 = localDateTime.plusMinutes(-1);//2020-11-11 11:11:59 -1分钟，localDateTime4=2020-11-11 11:10:59
LocalDateTime localDateTime5 = localDateTime.plusHours(1);//2020-11-11 11:11:59 +1小时，localDateTime5=2020-11-11 12:11:59
LocalDateTime localDateTime6 = localDateTime.plusHours(-1);//2020-11-11 11:11:59 -1小时，localDateTime6=2020-11-11 10:11:59
LocalDateTime localDateTime7 = localDateTime.plusDays(1);//2020-11-11 11:11:59 +1天，localDateTime7=2020-11-12 11:11:59
LocalDateTime localDateTime8 = localDateTime.plusDays(-1);//2020-11-11 11:11:59 -1天，localDateTime8=2020-11-10 11:11:59
LocalDateTime localDateTime9 = localDateTime.plusMonths(1);//2020-11-11 11:11:59 +1月，localDateTime9=2020-12-11 11:11:59
LocalDateTime localDateTime10 = localDateTime.plusMonths(-1);//2020-11-11 11:11:59 -1月，localDateTime10=2020-10-11 11:11:59
LocalDateTime localDateTime11 = localDateTime.plusYears(1);//2020-11-11 11:11:59 +1年，localDateTime11=2021-11-11 11:11:59
LocalDateTime localDateTime12 = localDateTime.plusYears(-1);//2020-11-11 11:11:59 -1年，localDateTime12=2019-11-11 11:11:59

除了上面年月日时分秒的加减，还有周的加减plusWeeks(),纳秒的加减plusNanos()

plusNanos()的使用可参考链接https://www.yiibai.com/javatime/javatime_localtime_plusnanos.html

3、LocalDateTime 格式化

LocalDateTime localDateTime=LocalDateTime.now();
localDateTime.format(DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"))

 格式化 HH是24小时制，hh是12小时制

 LocalDateTime还有很多方法可以使用，比如获取月份等，可以看源码。