java8 LocalDateTime

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LocalDateTime

java8使用了LocalDateTime和DateTimeFormatter。比之前的Date和Carlendar有所改进。
DateTimeFormatter是线程安全的。DateTimeFormatter中很多属性使用了final修饰。

LocalDate: 只能设置仅含年月日的格式，表示没有时区的日期, LocalDate是不可变并且线程安全的
LocalTime: 只能设置仅含时分秒的格式，表示没有时区的时间, LocalTime是不可变并且线程安全的
LocalDateTime: 可以设置含年月日时分秒的格式 ， 表示没有时区的日期时间, LocalDateTime是不可变并且线程安全的

ZoneId: 时区ID，用来确定Instant和LocalDateTime互相转换的规则
Instant: 用来表示时间线上的一个点（瞬时）
Clock: 用于访问当前时刻、日期、时间，用到时区
Duration: 用秒和纳秒表示时间的数量（长短），用于计算两个日期的“时间”间隔

构建LocalDateTime对象：

	public  void generateLocalDate() {LocalDate date = LocalDate.of(2000, 1, 8);LocalDateTime dateTime = LocalDateTime.of(2020, 1, 8, 15, 16, 17);System.out.println("date：" + date);System.out.println("dateTime:" + dateTime);}

获取LocalDateTime的年月日：

	public  void getLocalDateTimeMonth() {LocalDateTime dateTime = LocalDateTime.of(2020, 1, 8, 15, 16, 17);int year=dateTime.getYear();int month=dateTime.getMonth().getValue();int day=dateTime.getDayOfMonth();System.out.println("dateTime对应的年份为："+year);System.out.println("dateTime对应的月份为："+month);System.out.println("dateTime对应的天数为："+day);}

字符串String转LocalDateTime：

	public  void stringToTime() {DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");String datetimeText = "2020-04-01 23:59:59";LocalDateTime localDateTime = LocalDateTime.parse(datetimeText, formatter);// LocalDateTime的toString()方法，在日期和时间中间加入了"T"字符串System.out.println(localDateTime);}

LocalDateTime 转字符串String：

	public  void localDateTimeToString() {DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");LocalDateTime dateTime = LocalDateTime.of(2020, 1, 8, 15, 16, 17);String dateTimeStr = dateTime.format(formatter);System.out.println("dateTimeStr为：" + dateTime);}

LocalDateTime 转时间戳毫秒

      public static long getMillsByLocalDateTime(LocalDateTime localDateTime) {long mills = localDateTime.toInstant(ZoneOffset.of("+8")).toEpochMilli();return mills;}

时间戳毫秒转LocalDateTime

    public static LocalDateTime getLocalDateTimeByMills() {long mills = 1640419285000L;LocalDateTime result = new Date(mills).toInstant().atOffset(ZoneOffset.of("+8")).toLocalDateTime();return result;}

Date转Instant：

        Instant instant= date.toInstant();

Instant转Date：

        Date date = Date.from(instant);

Date转LocalDateTime ：

public static void dateToLocalDateTime(Date date) {Instant dateInstant = date.toInstant();LocalDateTime localDateTime = LocalDateTime.ofInstant(dateInstant, ZoneId.systemDefault());}

LocalDateTime转Date：

    public static Date parse(LocalDateTime localDateTime) {return Date.from(localDateTime.atZone( ZoneId.systemDefault()).toInstant());}

LocalDateTime 获取LocalDate：

LocalDate localDate = localDateTime.toLocalDate();

LocalDateTime 获取LocalTime：

LocalTime localTime = localDateTime.toLocalTime();

LocalDate

Date转LocalDate：

    public void dateToLocalDate(Date date) {Instant dateInstant = date.toInstant();LocalDate localDate = LocalDateTime.ofInstant(dateInstant, ZoneId.systemDefault()).toLocalDate();}

LocalDate转Date：

    public static Date parse(LocalDate localDate) {return Date.from(localDate.atStartOfDay().atZone(ZoneId.systemDefault()).toInstant());}

localDate转String ：

public static String localDateToString(Date date) {Instant dateInstant = date.toInstant();LocalDate localDate = LocalDateTime.ofInstant(dateInstant, ZoneId.systemDefault()).toLocalDate();// localDate转String DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");String localDateStr = localDate.format(formatter);System.out.println(localDateStr);return localDateStr;}

String转LocalDate：

public static void stringToLocalDate() {DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");String datetimeText = "2020-04-01";LocalDate localDate = LocalDate.parse(datetimeText, formatter);System.out.println(localDate);}

LocalDate获取年月日:

    int year = localDate.getYear();int monthValue = localDate.getMonthValue();int dayOfMonth = localDate.getDayOfMonth();

LocalDate修改年月日：

    public static void changeYearMonthDay() {LocalDate localDate = LocalDate.now();//修改年份LocalDate withYearResult = localDate.withYear(2020);//修改月份LocalDate withMonthResult = localDate.withMonth(5);//修改日LocalDate withDayResult = localDate.withDayOfMonth(20);System.out.println( withYearResult + "，" + withMonthResult+ "，"+ withDayResult);}

LocalDate比较日期大小compareTo：

compareTo()方法
在两边相等（=）的情况下返回 0
在左边大于（>）右边时返回 1　
在左边小于（<）右边时返回 -1

      public static void localDateCompareTo() {DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");String datetimeText = "2020-04-01";LocalDate localDate = LocalDate.parse(datetimeText, formatter);LocalDate nowDate = LocalDate.now();System.out.println(localDate);System.out.println("nowDate:"+nowDate);if (nowDate.compareTo(localDate) < 0) {System.out.println("nowDate小于"+ datetimeText);} else {System.out.println("nowDate大于等于"+ datetimeText);}}

LocalDate比较日期的前后：

after 只在大于（>）情况下才为true　(相等时不会）
before 只在小于（<）情况下才为true　(相等时不会）

public static void isBeforeAfter() {DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");String datetimeText = "2020-04-01";LocalDate localDate = LocalDate.parse(datetimeText, formatter);LocalDate nowDate = LocalDate.now();System.out.println(localDate);System.out.println("nowDate:"+nowDate);if (nowDate.isBefore(localDate)) {System.out.println(nowDate+ "在"+ datetimeText +"之前");} else {System.out.println(nowDate+ "在"+ datetimeText +"之后");}}

获取日期差距 / 获取日期时间间隔 ：

public static void durationDateTime() {LocalDateTime date3 = LocalDateTime.now();LocalDateTime date4 = LocalDateTime.of(2018, 1, 13, 22, 30, 10);Duration duration = Duration.between(date3, date4);System.out.println(date3 + " 与 " + date4 + " 间隔  " + "\n"+ " 天 :" + duration.toDays() + "\n"+ " 时 :" + duration.toHours() + "\n"+ " 分 :" + duration.toMinutes() + "\n"+ " 毫秒 :" + duration.toMillis() + "\n"+ " 纳秒 :" + duration.toNanos() + "\n");}

日期时间计算：

	public void addMonthDay() {LocalDateTime dt = LocalDateTime.of(2020, 1, 26, 20, 30, 59);System.out.println(dt);// 加5天减3小时:LocalDateTime dt2 = dt.plusDays(5).minusHours(3);System.out.println(dt2); // 2019-10-31T17:30:59// 减1月:LocalDateTime dt3 = dt2.minusMonths(1);System.out.println(dt3); // 2019-09-30T17:30:59}

LocalTime

LocalTime获取时分秒：

        //获取小时int hour = localTime.getHour();int hour1 = localTime.get(ChronoField.HOUR_OF_DAY);//获取分int minute = localTime.getMinute();int minute1 = localTime.get(ChronoField.MINUTE_OF_HOUR);//获取秒int second = localTime.getMinute();int second1 = localTime.get(ChronoField.SECOND_OF_MINUTE);

参考资料：

https://www.liaoxuefeng.com/wiki/1252599548343744/1303871087444002
https://blog.csdn.net/weixin_38405253/article/details/100765007
https://www.jianshu.com/p/048ee8580639

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