Java8自从发布到现在也有很长一段时间里，新版本的java给我们带来了很多激动人心的新特性，其中Date与Time的新API简直给平时需要对时间日期的进行各种复杂操作的同学带来的新的福音，本文也主要从这一点出发来一起探索一下关于Data与Time的新特性
本文基本上以代码为主，文字为辅。 不会出现过多的文字，因为大部分代码简洁明了，一看变懂。
LocalDate
所有的关于 Data/Time 的新API都被收录在 java.time package 中，首先我们来看看 java.time.LocalDate ， LocalDate 表示了一个与时间无关的带特定格式 year-month-day 的日期。
// the current date
LocalDate currentDate = LocalDate.now();
// 2014-02-10
LocalDate tenthFeb2014 = LocalDate.of(2017, Month.FEBRUARY, 10);
// months values start at 1 (2014-08-01)
LocalDate firstAug2014 = LocalDate.of(2014, 8, 1);
// the 65th day of 2010 (2010-03-06)
LocalDate sixtyFifthDayOf2010 = LocalDate.ofYearDay(2010, 65);
LocalTime, LocalDateTime
LocalTime是一个不带日期的只关于时间的类，LocalDateTime是LocalTime与LocalDate的结合体。下面是有关于这两个类的用法：
LocalTime currentTime = LocalTime.now(); // current time
LocalTime midday = LocalTime.of(12, 0); // 12:00
LocalTime afterMidday = LocalTime.of(13, 30, 15); // 13:30:15
// 12345th second of day (03:25:45)
LocalTime fromSecondsOfDay = LocalTime.ofSecondOfDay(12345);
// dates with times, e.g. 2014-02-18 19:08:37.950
LocalDateTime currentDateTime = LocalDateTime.now();
// 2014-10-02 12:30
LocalDateTime secondAug2014 = LocalDateTime.of(2014, 10, 2, 12, 30);
// 2014-12-24 12:00
LocalDateTime christmas2014 = LocalDateTime.of(2014, Month.DECEMBER, 24, 12, 0);
通常情况下LocalDate/Time 会使用系统默认的时钟跟时区，如果你想查询其他时区的时间，可以用以下方法：
// current (local) time in Los Angeles
LocalTime currentTimeInLosAngeles = LocalTime.now(ZoneId.of("America/Los_Angeles"));
// current time in UTC time zone
LocalTime nowInUtc = LocalTime.now(Clock.systemUTC());
下面是一个综合使用LocalTime/Date 的例子：
LocalDate date = LocalDate.of(2014, 2, 15); // 2014-02-15
boolean isBefore = LocalDate.now().isBefore(date); // false
// information about the month
Month february = date.getMonth(); // FEBRUARY
int februaryIntValue = february.getValue(); // 2
int minLength = february.minLength(); // 28
int maxLength = february.maxLength(); // 29
Month firstMonthOfQuarter = february.firstMonthOfQuarter(); // JANUARY
// information about the year
int year = date.getYear(); // 2014
int dayOfYear = date.getDayOfYear(); // 46
int lengthOfYear = date.lengthOfYear(); // 365
boolean isLeapYear = date.isLeapYear(); // false
DayOfWeek dayOfWeek = date.getDayOfWeek();
int dayOfWeekIntValue = dayOfWeek.getValue(); // 6
String dayOfWeekName = dayOfWeek.name(); // SATURDAY
int dayOfMonth = date.getDayOfMonth(); // 15
LocalDateTime startOfDay = date.atStartOfDay(); // 2014-02-15 00:00
// time information
LocalTime time = LocalTime.of(15, 30); // 15:30:00
int hour = time.getHour(); // 15
int second = time.getSecond(); // 0
int minute = time.getMinute(); // 30
int secondOfDay = time.toSecondOfDay(); // 55800
除此之外，新的api还提供一个 Year 类， 下面我们来看看通过它我们能做些什么呢：
Year currentYear = Year.now();
Year twoThousand = Year.of(2000);
boolean isLeap = currentYear.isLeap(); // false
int length = currentYear.length(); // 365
// sixtyFourth day of 2014 (2014-03-05)
LocalDate date = Year.of(2014).atDay(64);
我们可以使用诸如 plus和minus 方法来对时间做一些基本的加减法。这些方法会返回一个新的相关的实例：
LocalDate tomorrow = LocalDate.now().plusDays(1);
// before 5 houres and 30 minutes
LocalDateTime dateTime = LocalDateTime.now().minusHours(5).minusMinutes(30);
TemporalAdjusters 是另外一个非常重要的操作时间日期的接口，它提供了不同的静态方法来提供对时间日期操作的支持：
LocalDate date = LocalDate.of(2014, Month.FEBRUARY, 25); // 2014-02-25
// first day of february 2014 (2014-02-01)
LocalDate firstDayOfMonth = date.with(TemporalAdjusters.firstDayOfMonth());
// last day of february 2014 (2014-02-28)
LocalDate lastDayOfMonth = date.with(TemporalAdjusters.lastDayOfMonth());
使用静态导入会让你的代码更加具有可读性
import static java.time.temporal.TemporalAdjusters.*;
...
// last day of 2014 (2014-12-31)
LocalDate lastDayOfYear = date.with(lastDayOfYear());
// first day of next month (2014-03-01)
LocalDate firstDayOfNextMonth = date.with(firstDayOfNextMonth());
// next sunday (2014-03-02)
LocalDate nextSunday = date.with(next(DayOfWeek.SUNDAY));
Time zones(时区)
如果你想将 date/time 与时区联系在一起的话，java提供了另外一个类 ZoneDateTIme 或者 OffsetDateTime
ZoneId losAngeles = ZoneId.of("America/Los_Angeles");
ZoneId berlin = ZoneId.of("Europe/Berlin");
// 2014-02-20 12:00
LocalDateTime dateTime = LocalDateTime.of(2014, 02, 20, 12, 0);
// 2014-02-20 12:00, Europe/Berlin (+01:00)
ZonedDateTime berlinDateTime = ZonedDateTime.of(dateTime, berlin);
// 2014-02-20 03:00, America/Los_Angeles (-08:00)
ZonedDateTime losAngelesDateTime = berlinDateTime.withZoneSameInstant(losAngeles);
int offsetInSeconds = losAngelesDateTime.getOffset().getTotalSeconds(); // -28800
// a collection of all available zones
Set<String> allZoneIds = ZoneId.getAvailableZoneIds();
// using offsets
LocalDateTime date = LocalDateTime.of(2013, Month.JULY, 20, 3, 30);
ZoneOffset offset = ZoneOffset.of("+05:00");
// 2013-07-20 03:30 +05:00
OffsetDateTime plusFive = OffsetDateTime.of(date, offset);
// 2013-07-19 20:30 -02:00
OffsetDateTime minusTwo = plusFive.withOffsetSameInstant(ZoneOffset.ofHours(-2));
TimeStamps 时间戳
LocalData 与ZonedDateTime 提供的时间日期方式都是人类可读的，但是如果我们需要从机器的角度来探索时间日期的话，我们可以使用这个类。即时计算从1970年1月1日（1970-01-01 00:00:00）的第一个秒开始的时间，也称为EPOCH。 即时值可以是负数，如果它们在时代之前发生。 它们遵循ISO 8601表示日期和时间的标准。
// current time
Instant now = Instant.now();
// from unix timestamp, 2010-01-01 12:00:00
Instant fromUnixTimestamp = Instant.ofEpochSecond(1262347200);
// same time in millis
Instant fromEpochMilli = Instant.ofEpochMilli(1262347200000l);
// parsing from ISO 8601
Instant fromIso8601 = Instant.parse("2010-01-01T12:00:00Z");
// toString() returns ISO 8601 format, e.g. 2014-02-15T01:02:03Z
String toIso8601 = now.toString();
// as unix timestamp
long toUnixTimestamp = now.getEpochSecond();
// in millis
long toEpochMillis = now.toEpochMilli();
// plus/minus methods are available too
Instant nowPlusTenSeconds = now.plusSeconds(10);
Periods, Durations
这是另外两个非常有用也很重要的类。Period主要使用基于date（日期）的值,例如 years, months, days 来代表一段时间。Duration则是基于秒或者毫秒的。 他们的值可以是负数，如果结束时间发生在起始时间之前。
// periods
LocalDate firstDate = LocalDate.of(2010, 5, 17); // 2010-05-17
LocalDate secondDate = LocalDate.of(2015, 3, 7); // 2015-03-07
Period period = Period.between(firstDate, secondDate);
int days = period.getDays(); // 18
int months = period.getMonths(); // 9
int years = period.getYears(); // 4
boolean isNegative = period.isNegative(); // false
Period twoMonthsAndFiveDays = Period.ofMonths(2).plusDays(5);
LocalDate sixthOfJanuary = LocalDate.of(2014, 1, 6);
// add two months and five days to 2014-01-06, result is 2014-03-11
LocalDate eleventhOfMarch = sixthOfJanuary.plus(twoMonthsAndFiveDays);
// durations
Instant firstInstant= Instant.ofEpochSecond( 1294881180 ); // 2011-01-13 01:13
Instant secondInstant = Instant.ofEpochSecond(1294708260); // 2011-01-11 01:11
Duration between = Duration.between(firstInstant, secondInstant);
// negative because firstInstant is after secondInstant (-172920)
long seconds = between.getSeconds();
// get absolute result in minutes (2882)
long absoluteResult = between.abs().toMinutes();
// two hours in seconds (7200)
long twoHoursInSeconds = Duration.ofHours(2).getSeconds();
Formatting, Parsing
/ 2014-04-01 10:45
LocalDateTime dateTime = LocalDateTime.of(2014, Month.APRIL, 1, 10, 45);
// format as basic ISO date format (20140220)
String asBasicIsoDate = dateTime.format(DateTimeFormatter.BASIC_ISO_DATE);
// format as ISO week date (2014-W08-4)
String asIsoWeekDate = dateTime.format(DateTimeFormatter.ISO_WEEK_DATE);
// format ISO date time (2014-02-20T20:04:05.867)
String asIsoDateTime = dateTime.format(DateTimeFormatter.ISO_DATE_TIME);
// using a custom pattern (01/04/2014)
String asCustomPattern = dateTime.format(DateTimeFormatter.ofPattern("dd/MM/yyyy"));
// french date formatting (1. avril 2014)
String frenchDate = dateTime.format(DateTimeFormatter.ofPattern("d. MMMM yyyy", new Locale("fr")));
// using short german date/time formatting (01.04.14 10:45)
DateTimeFormatter formatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.SHORT)
.withLocale(new Locale("de"));
String germanDateTime = dateTime.format(formatter);
// parsing date strings
LocalDate fromIsoDate = LocalDate.parse("2014-01-20");
LocalDate fromIsoWeekDate = LocalDate.parse("2014-W14-2", DateTimeFormatter.ISO_WEEK_DATE);
LocalDate fromCustomPattern = LocalDate.parse("20.01.2014", DateTimeFormatter.ofPattern("dd.MM.yyyy"));
在不同的 date/time 对象之间的转换
// LocalDate/LocalTime <-> LocalDateTime
LocalDate date = LocalDate.now();
LocalTime time = LocalTime.now();
LocalDateTime dateTimeFromDateAndTime = LocalDateTime.of(date, time);
LocalDate dateFromDateTime = LocalDateTime.now().toLocalDate();
LocalTime timeFromDateTime = LocalDateTime.now().toLocalTime();
// Instant <-> LocalDateTime
Instant instant = Instant.now();
LocalDateTime dateTimeFromInstant = LocalDateTime.ofInstant(instant, ZoneId.of("America/Los_Angeles"));
Instant instantFromDateTime = LocalDateTime.now().toInstant(ZoneOffset.ofHours(-2));
// convert old date/calendar/timezone classes
Instant instantFromDate = new Date().toInstant();
Instant instantFromCalendar = Calendar.getInstance().toInstant();
ZoneId zoneId = TimeZone.getDefault().toZoneId();
ZonedDateTime zonedDateTimeFromGregorianCalendar = new GregorianCalendar().toZonedDateTime();
// convert to old classes
Date dateFromInstant = Date.from(Instant.now());
TimeZone timeZone = TimeZone.getTimeZone(ZoneId.of("America/Los_Angeles"));
GregorianCalendar gregorianCalendar = GregorianCalendar.from(ZonedDateTime.now());
现在来看， 对于时间跟日期的操作真的是比以往方便了很多，我们可以彻底告别各种蛋疼的逻辑操作了。
