java8 日期实践

LocalDate类

生成LocalDate的几种方式

LocalDate localDate=LocalDate.now();
        System.out.println(localDate);

        LocalDate now =LocalDate.of(2020, 3, 9);
        System.out.println(now);
        //有个坑 ，如果是2020-3-9表示或者2020-03-9 或者2020-3-09表示就不行必须yyyy-mm-dd格式
        LocalDate localDate1=LocalDate.parse("2020-03-09");
        System.out.println(localDate1);

LocalTime类

LocalTime now=LocalTime.now();
     System.out.println(now);
     LocalTime now1=LocalTime.of(11, 28);
     System.out.println(now1);
     //默认格式为yyyy-mm-dd hh:mm:ss
     LocalTime now2=LocalTime.parse("11:28");
     System.out.println(now2);

MonthDay (用来判断是否是生日)

public static Boolean isBirthDay(int year,int month,int day){
     LocalDate currentDate=LocalDate.of(year, month, day);
     MonthDay birthDay=MonthDay.from(currentDate);
     LocalDate now=LocalDate.now();
     MonthDay currentMonthDay=MonthDay.from(now);
     if (birthDay.equals(currentMonthDay)){
         return true;
     }
     return  false;
 }

对LocalDate的加减(一年后，一年后，一天后)

   LocalDate now=LocalDate.now();

     LocalDate oneWeekLater=now.plusWeeks(1);
     System.out.println(oneWeekLater);

     LocalDate oneDayLater=now.plusDays(1);
     System.out.println(oneDayLater);
     LocalDate                                       oneMonthLater=now.plusMonths(1);
     System.out.println(oneMonthLater);
     
     LocalDate oneYearLater=now.plusYears(1);
     System.out.println(oneYearLater);

获取LocalDate中的year month day

LocalDate now=LocalDate.now();
int year=now.getYear();
     /**
         * getMonth()返回的是英语的月份 
         */
        int month=now.getMonthValue();
       int dayOfMonth  = now.getDayOfMonth();
        System.out.println(year);
        System.out.println(month);
        System.out.println(dayOfMonth);

日期的比较（早，晚 或者相等）

LocalDate now=LocalDate.now();
LocalDate now1=LocalDate.of(2020,03,09);
System.out.println(now.isBefore(now1));
System.out.println(now.isAfter(now1));
System.out.println(now.isEqual(now1));

Instant 类(常用类 获取当前时间戳)

Instant instant=Instant.now();
        System.out.println(instant.toEpochMilli());

Period类 （表示时间段 2个LocalDate之间的差）

LocalDate now=LocalDate.now();
LocalDate now1=LocalDate.of(2020,03,09);
Period period=Period.between(now,now1);
System.out.println(period.getYears());
System.out.println(period.getDays());
System.out.println(period.getMonths());

Duration类（表示时间差 比如2个LocalTime之间的时间差）

LocalTime localTimeNow=LocalTime.now();
        LocalTime localTime=LocalTime.of(11, 03);
        Duration duration=Duration.between(localTime, localTimeNow);
        System.out.println(duration.getSeconds());

YearMonth类

与 MonthDay检查重复事件的例子相似，YearMonth是另一个组合类，用于表示信用卡到期日、FD到期日、期货期权到期日等。还可以用这个类得到 当月共有多少天，YearMonth实例的lengthOfMonth()方法可以返回当月的天数，在判断2月有28天还是29天时非常有用。

YearMonth currentYearMonth = YearMonth.now();
     System.out.printf("Days in month year %s: %d%n", currentYearMonth, currentYearMonth.lengthOfMonth());
     YearMonth creditCardExpiry = YearMonth.of(2019, Month.FEBRUARY);
     System.out.printf("Your credit card expires on %s %n", creditCardExpiry);

日期字符串和日期互相转换以及自定义日期格式

 LocalDateTime date = LocalDateTime.now();

        DateTimeFormatter format1 = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        //日期转字符串
        String str = date.format(format1);

        System.out.println("日期转换为字符串:"+str);

        DateTimeFormatter format2 = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss");
        //字符串转日期
        LocalDate date2 = LocalDate.parse(str,format2);
        System.out.println("日期类型:"+date2);

判断是否闰年（isLeapYear()）

 LocalDate today = LocalDate.now();
        if(today.isLeapYear()){
            System.out.println("This year is Leap year");
        }else {
            System.out.println("2018 is not a Leap year");
        }

LocalDateTime 是LocalDate和LocalTime的集合体

Clock类（用来获取当前时间戳）

 Clock clock = Clock.systemUTC();
        System.out.println("Clock : " + clock.millis());

        // Returns time based on system clock zone
        Clock defaultClock = Clock.systemDefaultZone();
        System.out.println("Clock : " + defaultClock.millis());