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三个时间类
LocalDate、LocalTime、LocalDateTime
第一个只负责日期相关的处理，第二个负责时间相关的处理，第三个日期时间一起处理，其本质是前两者操作的再封装。
获取当前时间
LocalDateTime now = LocalDateTime.now();
//output : 2018-09-04T14:16:05.323获取自定义时间
指定字符串:
LocalDateTime nationalDay = LocalDateTime.of(2018, Month.OCTOBER, 1, 14, 30);
// output : 2018-10-01T14:30指定数字:
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
LocalDateTime someDay = LocalDateTime.parse("2018-10-01 14:30:30", formatter);
// output : 2018-10-01T14:30:30日期时间格式化
DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
String nowStr = now.format(formatter);
// output : 2018-09-04 14:37:32日期比较大小
// LocalDateTime.now() == 2018-09-04 14:42:59
boolean nowIsBefore = LocalDateTime.now().isBefore(nationalDay);// nationalDay == 2018-10-01T14:30:30
// output : true
boolean nowIsAfter = LocalDateTime.now().isAfter(nationalDay);// nationalDay == 2018-10-01T14:30:30
// output : false日期相差多少年 | 月 | 天 | 小时 | 分钟 | 秒
// now = 2018-09-04T14:50:34.857 ; nationalDay == 2018-10-01T14:30:30
long diffYears = ChronoUnit.YEARS.between(LocalDateTime.now(), nationalDay);
// output : 0
long diffMonths = ChronoUnit.MONTHS.between(LocalDateTime.now(), nationalDay);
// output : 0
long diffDays = ChronoUnit.DAYS.between(LocalDateTime.now(), nationalDay);
// output : 26
long diffHours = ChronoUnit.HOURS.between(LocalDateTime.now(), nationalDay);
// output : 647
long diffMins = ChronoUnit.MINUTES.between(LocalDateTime.now(), nationalDay);
// output ：38859
long diffSecs = ChronoUnit.SECONDS.between(LocalDateTime.now(), nationalDay);
// output : 2331188
获取分钟
最简单
int mins2 = LocalDateTime.now().getMinute();
// output : 26最万能 (用于非默认语义，如天的分钟数)
long mins = LocalDateTime.now().getLong(ChronoField.MINUTE_OF_HOUR);
// output : 26
long mins = LocalDateTime.now().getLong(ChronoField.MINUTE_OF_DAY);
// output : 926两个特殊枚举
Month、DayOfWeek
获取星期
LocalDateTime sunDay = LocalDateTime.of(2018, 9, 2, 0, 0);
DayOfWeek dayOfWeek = sunDay.getDayOfWeek();
// output : SUNDAY
int dayOfWeek = sunDay.getDayOfWeek().getValue();
// output : 7获取月份
Month month = LocalDateTime.now().getMonth();
// output : SEPTEMBER
int month = LocalDateTime.now().getMonth().getValue();
// output : 9获取年份
int year = LocalDateTime.now().getYear();
// output : 2018
Year year = Year.now();
// output : 2018