Java8 日期时间操作

操作包括

1. java.util.Date().getTime()返回13位时间戳
2. System.currentTimeMillis 计算毫秒差
3. SimpleDateFormat 解析和格式化日期
4. LocalDate
5. LocalTime
6. LocalDateTime
7. Duration
8. Period
9. 计算日间隔 toEpochDay
10. 日期相互加减
11. 日期时间和日期相互转换
12. 时间类型和时间戳互相转化

java.util.Date().getTime()

返回13位时间戳

        long a = new java.util.Date().getTime();
        System.out.println(a);  // 1602243261784

System.currentTimeMillis

常用来计时, 单位是毫秒

// 使用 System.currentTimeMillis
    // 主要用来计算时间差
    public static void getDiffTime() {
        try {
            long start = System.currentTimeMillis();
            Thread.sleep(1000);
            long end = System.currentTimeMillis();
            System.out.println(end - start);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

SimpleDateFormat

常用来解析和格式化日期

// SimpleDateFormat 常用来输出标准格式日期
    // yyyy-MM-dd HH:mm:ss
    public static void getFormatDate() {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println(simpleDateFormat.format(new Date()));
    }

    public static void getParseDate() {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        try {
            Date date = simpleDateFormat.parse("2020-02-02");
            System.out.println(date);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

LocalDate

获得日期类型的时间, 并且获得年月日

// LocalDate 获得当前日期, 并且获得年. 月, 日
    public static void getNowDate() {
        LocalDate date = LocalDate.now();
        System.out.println(date);
        System.out.println(date.getDayOfMonth());
        System.out.println(date.getMonthValue());
        System.out.println(date.getYear());

        // 可以format
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd-MM-yyyy");
        String formatDate = date.format(formatter);
        System.out.println(formatDate);
    }

LocalTime

获得当前的日期时间, 并且获得时,分,秒

// LocalTime, 获得当前的日期时间, 并且获得时,分,秒
    public static void getNowTime() {
        LocalTime time = LocalTime.now();  // 20:13:56.241
        System.out.println(time);
        System.out.println(time.getHour());
        System.out.println(time.getMinute());
        System.out.println(time.getSecond());

        // 可以format
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("HH:mm:ss");
        String formatTime = time.format(formatter);
        System.out.println(formatTime);
    }

LocalDateTime

获得当前的日期时间, 并且获得年月日时分秒

// LocalDateTime, 获得当前的日期时间, 并且获得年月日时分秒
    public static void getNowDateTime() {
        LocalDateTime datetime = LocalDateTime.now();
        System.out.println(datetime);
        System.out.println(datetime.getYear());
        System.out.println(datetime.getDayOfMonth());
        System.out.println(datetime.getMonthValue());
        System.out.println(datetime.getHour());
        System.out.println(datetime.getMinute());
        System.out.println(datetime.getSecond());

        // format
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String formatDatetime = datetime.format(dateTimeFormatter);
        System.out.println(formatDatetime);  // 2020-07-17 09:22:54
    }

获得指定时间类型的数据

可以使用parse解析输入的字符串

// 指定日期时间
    public static void getTimeDefine() {
        String time1 = "2020-02-02";
        String time2 = "2020-02-02 15:03";
        String time3 = "16:20:20";
        LocalDate time1Parse = LocalDate.parse(time1);
        System.out.println(time1Parse);
        System.out.println(time1Parse.getDayOfMonth());

        LocalDateTime time2Parse = LocalDateTime.parse(time2, DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm"));
        System.out.println(time2Parse);
        System.out.println(time2Parse.getHour());
        System.out.println(time2Parse.getSecond());  // 默认是0
        // 解析之后再格式化输出
        System.out.println(time2Parse.format(DateTimeFormatter.ofPattern("yyyy:MM:dd HH:mm:ss")));

        LocalTime time3Parse = LocalTime.parse(time3);
        System.out.println(time3Parse);
        System.out.println(time3Parse.getHour());
        System.out.println(time3Parse.format(DateTimeFormatter.ofPattern("HH:mm")));
    }

或者使用of方法

public static void getTimeDefine2() {
        LocalDateTime time1 = LocalDateTime.of(2020, 2, 3, 13, 2, 33);
        System.out.println(time1);
        System.out.println(time1.getYear());
        System.out.println(time1.getSecond());

        LocalDate time2 = LocalDate.of(2020, 2, 3);
        System.out.println(time2);
        System.out.println(time2.getDayOfMonth());
        System.out.println(time2.getYear());
    }

Duration

时间区间, 使用秒和纳秒衡量, 只能用DateTime

// 计算日期差
    public static void getDiffDate() {
        // Duration用秒和纳秒衡量时间, 所以只能用LocalDateTime
        LocalDateTime date1 = LocalDateTime.parse("2020-02-02 00:00:00", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss"));
        LocalDateTime date2 = LocalDateTime.of(2020, 4, 2, 0, 0, 0);
        Duration duration = Duration.between(date1, date2);
        System.out.println(duration.toString());  // PT-744H
        System.out.println(duration.toDays());  // 后 - 前
        System.out.println(duration.toHours());
        System.out.println(duration.toMillis());
    }

Period

时间区间, 衡量年月日和几天之间的时间值

// 计算日期差Period
    public static void getDiddDate2() {
        // Period
        // 计算间隔多少年月天, 以大单位先开始排, toTotalMonths可以获得总共间隔多少月
        LocalDate date1 = LocalDate.of(2018, 2, 2);
        LocalDate date2 = LocalDate.of(2020, 1, 10);
        Period period = Period.between(date1, date2);
        System.out.println(period.getYears());
        System.out.println(period.getDays());
        System.out.println(period.getMonths());
        System.out.println(period.toTotalMonths());
        System.out.printf("区间间隔%d年%d月%d天\n", period.getYears(), period.getMonths(), period.getDays());
    }

toEpochDay 计算相差多少日

// 计算日期相差多少天
    public static void getDiffDay() {
        LocalDate date1 = LocalDate.of(2020, 2, 3);
        LocalDate date2 = LocalDate.of(2020, 1, 19);
        long date1EpochDay = date1.toEpochDay();  // 返回的是距离1970-01-01的天数
        System.out.println(date1EpochDay);
        long diffDays = date1.toEpochDay() - date2.toEpochDay();
        System.out.println(diffDays);
    }

日期相加减

// 日期相加减
    public static void plusMinDay() {
        LocalDate date1 = LocalDate.of(2020, 2, 3);
        LocalDate date2 = date1.plusDays(3);
        System.out.println(date2);
        LocalDate date3 = date1.plusYears(2);
        System.out.println(date3);
        LocalDate date4 = date1.minusDays(10);
        System.out.println(date4);
        LocalDate date5 = date1.minusDays(-10);
        System.out.println(date5);
    }

时间, 日期, 日期时间之间的互相转化

// time, date, datetime之间互相转化
    public static void dateToTimeStamp() {
        // date => datetime    asTime
        LocalDate date1 = LocalDate.of(2020, 1, 2);
        LocalDateTime time1 = date1.atTime(LocalTime.parse("06:30:20"));
        LocalDateTime time2 = date1.atTime(LocalTime.of(6,30,30));
        System.out.println(time1.toString());
        System.out.println(time2.toString());

        // time => datetime
        LocalTime time6 = LocalTime.of(13, 13, 13);
        LocalDateTime date3 = time6.atDate(LocalDate.parse("2020-02-02"));
        System.out.println(date3);

        // datetime => date / time
        LocalDateTime time3 = LocalDateTime.of(2020, 2, 2, 13, 1, 1);
        LocalDate date2 = time3.toLocalDate();
        System.out.println(date2.toString());
        LocalTime time4 = time3.toLocalTime();
        System.out.println(time4);
    }

时间类型和时间戳互相转化

// 转化为时间戳
    public static void dateTimeToTimestamp() {
        // datetime转时间戳
        LocalDateTime time1 = LocalDateTime.of(2020,2,2,2,2,2);
        long timestrap = time1.atZone(ZoneId.systemDefault()).toInstant().toEpochMilli();
        System.out.println(timestrap);  // 1580580122000   13位时间戳

        // 时间戳转datetime
        Instant instant = Instant.ofEpochMilli(1580580122000L);
        LocalDateTime time2 = LocalDateTime.ofInstant(instant, ZoneId.systemDefault());
        System.out.println(time2.toString());

    }