Java 8 之 新日期时间API

Joda-Time作者Stephen Colebourne领导完成的JSR-310已经随着Java 8的Release正式发布。JSR-310的API和Joda-Time是兼容的，但经过了重新设计。Google一下网上已经有很多介绍，有人说JSR-310有些过度设计，“不管你喜不喜欢他，他都带着诚意扑面而来了”。

Joda-Time的介绍：http://rensanning.iteye.com/blog/1546652

关于JSR-310 和 Joda-Time
http://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html
https://www.infoq.com/news/2010/03/jsr-310
http://blog.joda.org/2010/12/what-about-jsr-310_153.html
http://blog.joda.org/2014/11/converting-from-joda-time-to-javatime.html

（1）系统时间

LocalDate date = LocalDate.now();
System.out.println(date.getYear() + "/" + date.getMonthValue() + "/" + date.getDayOfMonth()); // 2014/3/21

LocalTime time = LocalTime.now();
System.out.println(time.getHour() + ":" + time.getMinute() + ":" + time.getSecond()); // 16:39:22
// ***没有提供  getMillis() 方法
System.out.println(time.get(ChronoField.MILLI_OF_SECOND)); // 859

LocalDateTime dateTime = LocalDateTime.now();
System.out.println(dateTime.getYear() + "/" + dateTime.getMonthValue() + "/" + dateTime.getDayOfMonth()
		   + " " + dateTime.getHour() + ":" + dateTime.getMinute() + ":" + dateTime.getSecond()); // 2014/3/21 16:39:22

Clock clock = Clock.systemDefaultZone();
System.out.println(clock.millis()); // 1395391162859

（2）特定日期

LocalDate myDate = LocalDate.of(2013, 12, 4);
System.out.println(myDate.getYear() + "/" + myDate.getMonthValue() + "/" + myDate.getDayOfMonth()); // 2013/12/4

LocalDate independenceDay = LocalDate.of(2014, Month.JULY, 4);
DayOfWeek dayOfWeek = independenceDay.getDayOfWeek();
System.out.println(dayOfWeek);    // FRIDAY

LocalTime myTime = LocalTime.of(10, 30, 45);
System.out.println(myTime.getHour() + ":" + myTime.getMinute() + ":" + myTime.getSecond()); // 10:30:45

LocalDateTime myDateTime1 = LocalDateTime.of(2013, 12, 4, 10, 30, 45);
System.out.println(myDateTime1.getYear() + "/" + myDateTime1.getMonthValue() + "/" + myDateTime1.getDayOfMonth()
		   + " " + myDateTime1.getHour() + ":" + myDateTime1.getMinute() + ":" + myDateTime1.getSecond()); // 2013/12/4 10:30:45

LocalDateTime myDateTime2 = LocalDateTime.of(myDate, myTime);
System.out.println(myDateTime2.getYear() + "/" + myDateTime2.getMonthValue() + "/" + myDateTime2.getDayOfMonth()
		   + " " + myDateTime2.getHour() + ":" + myDateTime2.getMinute() + ":" + myDateTime2.getSecond()); // 2013/12/4 10:30:45

（3）格式化

// Date -> String
LocalDate formatDate1 = LocalDate.of(2013, 12, 4);
String dateString = formatDate1.format(DateTimeFormatter.ofPattern("yyyy/MM/dd"));
System.out.println(dateString); // 2013/12/04

// String -> Date
LocalDate formatDate2 = LocalDate.parse("2013/12/04", DateTimeFormatter.ofPattern("yyyy/MM/dd"));
System.out.println(formatDate2); // 2013-12-04

（4）日期转换

// LocalDate -> LocalDateTime
LocalDate changeDate1 = LocalDate.of(2013, 12, 4);
LocalDateTime changeDateTime1 = changeDate1.atTime(10, 30, 45);
System.out.println(changeDateTime1); // 2013-12-04T10:30:45
 
// LocalTime -> LocalDateTime
LocalTime time2 = LocalTime.of(10, 30, 45);
LocalDateTime dateTime2 = time2.atDate(LocalDate.of(2013, 12, 4));
System.out.println(dateTime2); // 2013-12-04T10:30:45
 
// LocalDateTime -> LocalDate, LocalTime
LocalDateTime dateTime3 = LocalDateTime.of(2013, 12, 4, 10, 30, 45);
LocalDate date3 = dateTime3.toLocalDate();
System.out.println(date3); // 2013-12-04
LocalTime time3 = dateTime3.toLocalTime();
System.out.println(time3); // 10:30:45

（5）日期加减

LocalDate today = LocalDate.now();
LocalDate twoDaysAfter = today.plusDays(2L); // 2天后
LocalDate threeDaysBefore = today.minusDays(3L); // 3天前
LocalDate oneYearsAfter = today.plus(1L, ChronoUnit.YEARS);// 1年后
LocalDate twoWeeksBefore = today.minus(2L, ChronoUnit.WEEKS); // 2周前
LocalDate newDate = LocalDate.now().plus(Period.of(3, 2, 1)); // 3年2月1天后

（6）计算间隔

LocalDateTime d1 = LocalDateTime.of(2013, 11, 4, 10, 30, 45);
LocalDateTime d2 = LocalDateTime.of(2013, 12, 4, 10, 30, 45);
Duration duration = Duration.between(d1, d2);
System.out.println(duration.toDays()); // 30

（7）日期比较

LocalDate compDate1 = LocalDate.of(2013, 12, 4);
LocalDate compDate2 = LocalDate.of(2013, 11, 4);
System.out.println(compDate1.isBefore(compDate2)); // false
System.out.println(compDate1.compareTo(compDate2)); // 1

       
（8）和java.util.Date的转换

// LocalDateTime -> Date
LocalDateTime cDateTime = LocalDateTime.now();
Instant instant = cDateTime.atZone(ZoneId.systemDefault()).toInstant();
Date cDate = Date.from(instant);
System.out.println(cDate); // Fri Mar 21 16:39:22 CST 2014
 
// Date -> LocalDateTime
Date date2 = new Date();
Instant instant2 = date2.toInstant();
LocalDateTime dateTimeFromDate = LocalDateTime.ofInstant(instant2, ZoneOffset.systemDefault());
System.out.println(dateTimeFromDate); // 2014-03-21T16:39:22.890

// Calendar -> LocalDateTime
Calendar cal = Calendar.getInstance();
LocalDateTime dateTimeFromCal = LocalDateTime.ofInstant(cal.toInstant(), ZoneOffset.systemDefault());
System.out.println(dateTimeFromCal); // 2014-03-21T16:39:22.890

关于java.util.Date这篇文章说的很详细：
https://codeblog.jonskeet.uk/2017/04/23/all-about-java-util-date/

（9）时区

ZoneId zoneId = ZoneId.systemDefault();
System.out.println(zoneId.toString()); // Asia/Shanghai

ZoneOffset zoneOffset = ZoneOffset.ofHours(1);
System.out.println(zoneOffset.toString()); // +01:00

ZoneId zone1 = ZoneId.of("Asia/Tokyo");
System.out.println(zone1.getRules()); // ZoneRules[currentStandardOffset=+09:00]
LocalTime now1 = LocalTime.now(zone1);
System.out.println(now1); // 17:39:22.890

ZonedDateTime jaTime = ZonedDateTime.of(2014, 1, 31, 10, 0, 0, 0, zone1);
System.out.println(jaTime); // 2014-01-31T10:00+09:00[Asia/Tokyo]

（10）日本时间

JapaneseDate jdate1 = JapaneseDate.of(2013, 12, 4);
System.out.println(jdate1); // Japanese Heisei 25-12-04    
JapaneseDate jdate2 = JapaneseDate.of(JapaneseEra.HEISEI, 25, 12, 4);
System.out.println(jdate2); // Japanese Heisei 25-12-04

http://blog.joda.org/2009/11/why-jsr-310-isn-joda-time_4941.html
http://java.dzone.com/articles/deeper-look-java-8-date-and
http://www.coppermine.jp/docs/programming/2013/12/jsr310-tips.html