【java】java8 time

1.前言

Java 8 之前的 时间api 一直不太理想，后来出现了 标准的 日期 时间 类库—— Joda-time

Java 8  增加了 java.time 包，实现了 JSR-310 协议

2.api 介绍

// 以下api 均是不可变的并且是线程安全的

ZonedDateTime: 带有 时区 的 日期时间,存储了所有的日期，时间字段，例如：2007-12-03T10:15:30+01:00 Europe/Paris ;
LocalDateTime: 不带有 时区的 日期时间，只保存了 年月日时分秒，例子：2018-03-13T11:32:35.890 ;
LocalDate: 不带有 时区的 日期，只保存了 年月日。例子：2007-12-03 ;
LocalTime: 不带有 时区的 时间，可以精确到纳秒 级别. 例子：11:31:40.633 ;

3.相互转化

long 转 localDateTime  : long 转 Instant , Instant 转 LocalDateTime

        LocalDateTime dateTime = LocalDateTime.ofInstant(
                Instant.ofEpochMilli(new Date().getTime()), ZoneId.systemDefault()
        );

localDateTime 转 long ：LocalDateTime 转ZonedDateTime ; ZonedDateTime 转 Instant；Instant  转Date; Date  最后转 long

        long time = Date.from(LocalDateTime.now().atZone(ZoneId.systemDefault()).toInstant())
                .getTime();

4. 常用util 类

获取当天的开始时间

    public static ZonedDateTime getStartOfDate(LocalDateTime localDateTime) {
        return localDateTime.toLocalDate().atStartOfDay(ZoneId.systemDefault());
    }

当天开始时间、结束时间

LocalDateTime.of(LocalDate.now(), LocalTime.MIN);//当天零点  
LocalDateTime.of(LocalDate.now(), LocalTime.MAX);//当天23点59分59秒

格式化说明：

Symbol  Meaning                     Presentation      Examples
  ------  -------                     ------------      -------
   G       era                         text              AD; Anno Domini; A
   u       year                        year              2004; 04
   y       year-of-era                 year              2004; 04
   D       day-of-year                 number            189
   M/L     month-of-year               number/text       7; 07; Jul; July; J
   d       day-of-month                number            10

   Q/q     quarter-of-year             number/text       3; 03; Q3; 3rd quarter
   Y       week-based-year             year              1996; 96
   w       week-of-week-based-year     number            27
   W       week-of-month               number            4
   E       day-of-week                 text              Tue; Tuesday; T
   e/c     localized day-of-week       number/text       2; 02; Tue; Tuesday; T
   F       week-of-month               number            3

   a       am-pm-of-day                text              PM
   h       clock-hour-of-am-pm (1-12)  number            12
   K       hour-of-am-pm (0-11)        number            0
   k       clock-hour-of-am-pm (1-24)  number            0

   H       hour-of-day (0-23)          number            0
   m       minute-of-hour              number            30
   s       second-of-minute            number            55
   S       fraction-of-second          fraction          978
   A       milli-of-day                number            1234
   n       nano-of-second              number            987654321
   N       nano-of-day                 number            1234000000

   V       time-zone ID                zone-id           America/Los_Angeles; Z; -08:30
   z       time-zone name              zone-name         Pacific Standard Time; PST
   O       localized zone-offset       offset-O          GMT+8; GMT+08:00; UTC-08:00;
   X       zone-offset 'Z' for zero    offset-X          Z; -08; -0830; -08:30; -083015; -08:30:15;
   x       zone-offset                 offset-x          +0000; -08; -0830; -08:30; -083015; -08:30:15;
   Z       zone-offset                 offset-Z          +0000; -0800; -08:00;

   p       pad next                    pad modifier      1

   '       escape for text             delimiter
   ''      single quote                literal           '
   [       optional section start
   ]       optional section end
   #       reserved for future use
   {       reserved for future use
   }       reserved for future use