Java 8 时间日期使用

一、日期时间

Java 8通过发布新的Date-Time API (JSR 310)来进一步加强对日期与时间的处理。java.util.Date和SimpleDateFormatter都不是线程安全的，而LocalDate和LocalTime和最基本的String一样，是不变类型，不但线程安全，而且不能修改。以下为一些常用时间对象：

• Instant：表示时刻，不直接对应年月日信息，需要通过时区转换
• LocalDateTime: 表示与时区无关的日期和时间信息，不直接对应时刻，需要通过时区转换
• LocalDate：表示与时区无关的日期，与LocalDateTime相比，只有日期信息，没有时间信息
• LocalTime：表示与时区无关的时间，与LocalDateTime相比，只有时间信息，没有日期信息
• ZonedDateTime： 表示特定时区的日期和时间
• ZoneId/ZoneOffset：表示时区

1、LocalDate

　      LocalDate now = LocalDate.now();
        LocalDate now1 = LocalDate.now(Clock.systemUTC());

        System.out.println(now);
        System.out.println(now1);

        LocalDate of = LocalDate.of(2019, 3, 6);
        //严格按照ISO yyyy-MM-dd验证，03写成3都不行
        LocalDate parse = LocalDate.parse("2019-03-06");
        System.out.println(of);
        System.out.println(parse);

        System.out.println("**************now****************");

        //当前开始时间
        System.out.println(now.atStartOfDay());
        //当月第一天日期
        System.out.println(now.with(TemporalAdjusters.firstDayOfMonth()));
        //本月第二天日期
        System.out.println(now.withDayOfMonth(2));
        //当月最后一天
        System.out.println(now.with(TemporalAdjusters.lastDayOfMonth()));
        System.out.println(now.getDayOfMonth());
        //当月下一天
        System.out.println(now.plusDays(1));
        //当月上一天
        System.out.println(now.minusDays(1));
        System.out.println(now.getDayOfWeek());
        //当月下一周
        System.out.println(now.plusWeeks(1));
        //当月上一周
        System.out.println(now.minusWeeks(1));
        System.out.println(now.getMonth() + "-" + now.getMonthValue());
        //当月下一个月
        System.out.println(now.plusMonths(1));
        //当月上一个月
        System.out.println(now.minusMonths(1));

        //时间比较
        System.out.println(now.isEqual(LocalDate.of(2019, 03, 06)));

2、LocalTime

        LocalTime now = LocalTime.now();
        //指定时区
        LocalTime now1 = LocalTime.now(Clock.system(ZoneId.systemDefault()));
        LocalTime now2 = LocalTime.now(Clock.systemUTC());

        System.out.println(now);
        System.out.println(now1);
        System.out.println(now2);

        System.out.println("************now************");
        //清除毫秒位
        System.out.println(now.withNano(0));
        //获取当前的小时
        System.out.println(now.getHour());
        //解析时间时间也是按照ISO格式识别，但可以识别以下3种格式： 12:00 12:01:02 12:01:02.345
        System.out.println(LocalTime.parse("11:58:12"));

        //时间比较
        LocalTime other = LocalTime.of(13, 45, 59);
        System.out.println(now.isBefore(other));
        System.out.println(now.isAfter(other));

3、LocalDateTime

        LocalDateTime now = LocalDateTime.now();
        LocalDateTime now1 = LocalDateTime.now(Clock.system(ZoneId.systemDefault()));
        LocalDateTime now2 = LocalDateTime.now(Clock.systemUTC());

        System.out.println(now);
        System.out.println(now1);
        System.out.println(now2); 
　　　　　//时间格式转换
        System.out.println(now.format(DateTimeFormatter.ofPattern(PATTERN_1)));
        System.out.println(now.format(DateTimeFormatter.ofPattern(PATTERN_2)));
        System.out.println(now.format(DateTimeFormatter.ofPattern(PATTERN_3)));

4、Date转换为LocalDateTime

　　/**
     * Date转换为LocalDateTime
     * @return LocalDateTime
     */
    public static LocalDateTime date2LocalDateTime() {
        Date date = new Date();
        LocalDateTime localDateTime = LocalDateTime.ofInstant(date.toInstant(), ZoneId.systemDefault());

        return localDateTime;
    }

5、LocalDateTime转换为Date

    /**
     * LocalDateTime转换为Date
     * @return Date
     */
    public static Date localDateTime2Date() {
        LocalDateTime now = LocalDateTime.now();
        Instant instant = now.atZone(ZoneId.systemDefault()).toInstant();

        Date date = Date.from(instant);

        return date;
    }

6、秒与纳秒级别上的一段时间间隔

    /**
     * 秒与纳秒级别上的一段时间
     */
    public static void duration() {

        LocalDateTime from = LocalDateTime.of(2018, Month.OCTOBER, 1, 0, 0, 0);
        LocalDateTime to = LocalDateTime.of(2019, Month.MARCH, 6, 23, 59, 59);

        Duration between = Duration.between(from, to);
        System.out.println(between.toDays());
        System.out.println(between.toHours());
    }

源码参照：Github