Java8新时间日期API的使用

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public class Demo2 {
    public static void main(String[] args) {
        //1.创建LocalDateTime，now不可变，和Calendar不同
        System.out.println("--------获取并打印时间------------");
        LocalDateTime now = LocalDateTime.now();
        System.out.println(now.toLocalTime());
        System.out.println(now.toLocalDate());
        System.out.println(now);

        //2.创建昨天
        System.out.println("--------创建昨天------------");
        LocalDateTime yesterday = LocalDateTime.of(2019, 8, 16, 10, 10);
        System.out.println(yesterday);

        //3.创建明天
        System.out.println("--------创建明天------------");
        LocalDateTime localDateTime = now.plusDays(1);
        System.out.println(localDateTime);

        //4.获取时间字段
        System.out.println("--------获取事件字段------------");
        System.out.println("年" + now.getYear());
        System.out.println("月" + now.getMonthValue());
        System.out.println("月的天" + now.getDayOfMonth());
        System.out.println("周的天" + now.getDayOfWeek());
        System.out.println("小时" + now.getHour());
        System.out.println("分钟" + now.getMinute());
        System.out.println("秒" + now.getSecond());
    }
}

//打印结果
--------获取并打印时间------------
22:54:37.491
2019-08-18
2019-08-18T22:54:37.491
--------创建昨天------------
2019-08-16T10:10
--------创建明天------------
2019-08-19T22:54:37.491
--------获取事件字段------------
年2019
月8
月的天18
周的天SUNDAY
小时22
分钟54
秒37

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//创建Instant类对象
Instant instant = Instant.now();

//打印当前时间
System.out.println(instant.toString());

//获取毫秒数
System.out.println(instant.toEpochMilli());

//获取昨天
Instant instant1 = Instant.ofEpochMilli(System.currentTimeMillis() - (60 * 60 * 24 * 1000));
System.out.println(instant1.toString());

//计算时间差
System.out.println(Duration.between(instant1, instant).toHours());

//获取世界各地时区列表
Set<String> availableZoneIds = ZoneId.getAvailableZoneIds();
for (String availableZoneId : availableZoneIds) {
	System.out.println(availableZoneId);
}

//获取系统默认时区
ZoneId zoneId = ZoneId.systemDefault();

//从ID获取一个 ZoneId的实例，确保该ID有效并且可供使用；然后打印出此ID的时区规则，允许执行计算
ZoneId zone2 = ZoneId.of("Brazil/East");
System.out.println(zone2.getRules());
//打印结果：
ZoneRules[currentStandardOffset=+08:00]

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//利用毫秒数，Date转为Instant，再转为LocalDateTime
Date date = new Date();
Instant instant2 = date.toInstant();

//定位时区，然后获取localDate
LocalDateTime localDateTime = instant2.atZone(ZoneId.systemDefault()).toLocalDateTime();
System.out.println(localDateTime);

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Instant instant3 = localDateTime.atZone(ZoneId.systemDefault()).toInstant();
Date date1 = Date.from(instant3);
System.out.println(date1.toLocaleString());

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//date.with返回一个LocalDate类结果，打印年月日
LocalDate date=LocalDate.now();
//下一个周5
System.out.println(date.with(TemporalAdjusters.next(DayOfWeek.FRIDAY)));
//下一个周2
System.out.println(date.with(TemporalAdjusters.next(DayOfWeek.TUESDAY)));
//下一个周日（周日为每周的第一天）
System.out.println(date.with(TemporalAdjusters.next(DayOfWeek.SUNDAY)));

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public class Demo4 {
    public static void main(String[] args) {
        LocalDate date = LocalDate.now();
        //时间格式化器
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy/M/d");
        //按照格式将字符串解析
        LocalDate parse = LocalDate.parse("2019/8/17", dtf);
        System.out.println(parse);
        //将现在时间按照固定格式转为字符串
        String format = dtf.format(LocalDate.now());
        System.out.println(format);
    }
}

//打印结果
2019-08-17
2019/8/18