新的日期和时间API

LocalDate,LocalTime,Instant,Duration,Period

• 使用LocalDate和LocalTime
  localdate是一个不可变的对象，只能提供简单的日期，并不包含当天的时间信息，也不附带任何与时区相关的信息。

     //日期
        LocalDate localDate = LocalDate.now();
        System.out.println(localDate);
        //创建实例
        LocalDate localDate1 = LocalDate.of(2018, 06, 9);
        System.out.println(
            localDate1.getYear() + "-" +
                localDate1.getMonthValue() + "-" +
                localDate1.getDayOfMonth());
        System.out.println(localDate1.get(ChronoField.YEAR));
        System.out.println(localDate1.get(ChronoField.MONTH_OF_YEAR));
        System.out.println(localDate1.get(ChronoField.DAY_OF_MONTH));
        LocalDate localDate2 = LocalDate.parse("2018-06-09", DateTimeFormatter.ofPattern("yyyy-MM-dd"));
        System.out.println("localDate2:" + localDate2);
        boolean before = localDate2.isBefore(LocalDate.now());
        System.out.println(before);

localtime只提供当天的时间信息。

       //时间
        LocalTime localTime = LocalTime.now();
        System.out.println(localTime);
        LocalTime localTime1 = LocalTime.of(12, 12, 12);
        System.out.println(localTime1.getHour() + ":" + localTime1.getMinute() + ":" + localTime1.getSecond());
        LocalTime localTime2 = LocalTime.parse("07:23:02", DateTimeFormatter.ofPattern("HH:mm:ss"));
        System.out.println(localTime2);

合并日期和时间，LocalDateTime,是LocalDate和LocalTime的合体。它同时表示日期和时间，但不带有时区信息。

       //日期+ 时间
        LocalDateTime localDateTime = LocalDateTime.now();
        System.out.println(localDateTime);
        LocalDateTime localDateTime1 = LocalDateTime.of(2018,06,9,12,12,12);
        System.out.println(localDateTime1);
        System.out.println(localDateTime1.toLocalDate());
        System.out.println(localDateTime1.toLocalTime());

• 机器的日期和时间格式
  对于人比较习惯的时间，然后对于计算机确是很不好理解，因此有了instant类对时间建模的方式。

      //instant
        Instant instant = Instant.now();
        System.out.println("instant:"+instant);
        System.out.println(instant.getEpochSecond());
        System.out.println(instant.getNano());
        Instant instant1 = Instant.ofEpochMilli(1);
        System.out.println(instant1);
        Instant instant2 = Instant.ofEpochSecond(2,1_000_000_000);
        System.out.println(instant2);

• 定义duration和period
  duration主要用于处理以秒和纳秒衡量时间的长短，它不能只传递日期作为参数。

      //duration + period
        Duration duration = Duration.between(localTime1,localTime2);
        System.out.println(duration.getSeconds());
        System.out.println(duration.getNano());
        System.out.println(duration.isZero());

        Period period = Period.between(localDate1,localDate2);
        System.out.println(period);
        System.out.println(period.getDays());
        System.out.println(period.getMonths());
        System.out.println(period.plusDays(1).getDays());

操作，解析和格式和日期

因为LocalDate是不可变的对象，要想修改它最好的当时是创建这个对象的一个副本，然后修改这个对象的副本，它不会影响原来的对象。修改的方式是采用withAttribute。

//withAttribute
        LocalDate localDate3 = LocalDate.now();
        LocalDate localDate4 = localDate3.withYear(2019);
        localDate3.with(ChronoField.YEAR, 2019);
        System.out.println("localDate3:" + localDate3 + "   localDate4:" + localDate4);
        LocalDate localDate5 = localDate3.plusDays(1);
        System.out.println(localDate5);
        LocalDateTime localDateTime2 = LocalDateTime.now();
        System.out.println(localDateTime2);
        LocalDateTime localDateTime3 = localDateTime2.withDayOfMonth(2);
        System.out.println(localDateTime3);
        LocalDateTime localDateTime4 = localDateTime2.plusDays(10);
        System.out.println(localDateTime4);

• 使用TemporalAdjuster
  TemporalAdjuster提供了十分丰富的更加复杂的日期操作，而这些方法的名称也十分的直观。可以通过工厂TemporalAdjusters来操作。

//TemporalAdjuster
        TemporalAdjuster temporalAdjuster = TemporalAdjusters.firstDayOfMonth();
        System.out.println(temporalAdjuster.adjustInto(localDate3));
        TemporalAdjuster temporalAdjuster1 = TemporalAdjusters.firstDayOfNextMonth();
        System.out.println(temporalAdjuster1.adjustInto(localDate3));
        TemporalAdjuster temporalAdjuster2 = TemporalAdjusters.lastDayOfMonth();
        System.out.println(temporalAdjuster2.adjustInto(localDate3));
        TemporalAdjuster temporalAdjuster3 = TemporalAdjusters.dayOfWeekInMonth(localDate3.getMonthValue(),localDate3.getDayOfWeek());
        System.out.println(temporalAdjuster3.adjustInto(localDate3));

• 打印输出以及解析日期
  DateTimeFormatter是常用的日期解析格式，它预定义了像Basic_ISO_DATE和ISO_LOCAL_DATE这样的常量。和老的dateformatter相比，DateTimeFormatter是线程安全的。

 //DateTimeFormatter
        LocalDateTime localDateTime5 = LocalDateTime.now();
        String format = localDateTime5.format(DateTimeFormatter.BASIC_ISO_DATE);
        System.out.println(format);
        String format1 = localDateTime5.format(DateTimeFormatter.ISO_LOCAL_DATE_TIME);
        System.out.println(format1);
        String format2 = localDateTime5.format(DateTimeFormatter.ISO_DATE);
        System.out.println(format2);

处理不同的时区和历法

时区的设置为：“{区域}/{城市}”。

      //zoneId
        ZoneId zoneId = ZoneId.of("Europe/Rome");
        System.out.println(zoneId);
        String id = ZoneId.systemDefault().getId();
        System.out.println(id);
        ZoneRules rules = ZoneId.systemDefault().getRules();
        System.out.println(rules);

当获取到zoneId之后可以和localdate,localdatetime,instant对象整合起来，构造为一个zonedatetime实例。

//zoneId
        ZoneId zoneId = ZoneId.of("Europe/Rome");
        System.out.println(zoneId);
        String id = ZoneId.systemDefault().getId();
        System.out.println(id);

        ZoneRules rules = ZoneId.systemDefault().getRules();
        System.out.println(rules);
        LocalDateTime localDateTime6 = LocalDateTime.now();
        ZonedDateTime zonedDateTime = localDateTime6.atZone(ZoneId.of("Europe/Rome"));
        System.out.println(zonedDateTime.getYear()+"-"+zonedDateTime.getMonthValue()+"-"+zonedDateTime.getDayOfMonth());