Java8自從發(fā)布到現(xiàn)在也有很長一段時(shí)間里俭正，新版本的java給我們帶來了很多激動(dòng)人心的新特性蕊唐，其中Date與Time的新API簡直給平時(shí)需要對時(shí)間日期的進(jìn)行各種復(fù)雜操作的同學(xué)帶來的新的福音，本文也主要從這一點(diǎn)出發(fā)來一起探索一下關(guān)于Data與Time的新特性
本文基本上以代碼為主，文字為輔琉闪。 不會出現(xiàn)過多的文字，因?yàn)榇蟛糠执a簡潔明了砸彬，一看變懂颠毙。
LocalDate
所有的關(guān)于 Data/Time 的新API都被收錄在 java.time package 中斯入，首先我們來看看 java.time.LocalDate ， LocalDate 表示了一個(gè)與時(shí)間無關(guān)的帶特定格式 year-month-day 的日期蛀蜜。
// 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是一個(gè)不帶日期的只關(guān)于時(shí)間的類刻两，LocalDateTime是LocalTime與LocalDate的結(jié)合體。下面是有關(guān)于這兩個(gè)類的用法：
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);
通常情況下LocalDate/Time 會使用系統(tǒng)默認(rèn)的時(shí)鐘跟時(shí)區(qū)滴某，如果你想查詢其他時(shí)區(qū)的時(shí)間磅摹，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());
下面是一個(gè)綜合使用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還提供一個(gè) Year 類霎奢， 下面我們來看看通過它我們能做些什么呢：
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);
我們可以使用諸如 plus和minus 方法來對時(shí)間做一些基本的加減法户誓。這些方法會返回一個(gè)新的相關(guān)的實(shí)例：
LocalDate tomorrow = LocalDate.now().plusDays(1);
// before 5 houres and 30 minutes
LocalDateTime dateTime = LocalDateTime.now().minusHours(5).minusMinutes(30);
TemporalAdjusters 是另外一個(gè)非常重要的操作時(shí)間日期的接口，它提供了不同的靜態(tài)方法來提供對時(shí)間日期操作的支持：
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());
使用靜態(tài)導(dǎo)入會讓你的代碼更加具有可讀性
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(時(shí)區(qū))
如果你想將 date/time 與時(shí)區(qū)聯(lián)系在一起的話幕侠，java提供了另外一個(gè)類 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 時(shí)間戳
LocalData 與ZonedDateTime 提供的時(shí)間日期方式都是人類可讀的帝美，但是如果我們需要從機(jī)器的角度來探索時(shí)間日期的話，我們可以使用這個(gè)類晤硕。即時(shí)計(jì)算從1970年1月1日（1970-01-01 00:00:00）的第一個(gè)秒開始的時(shí)間悼潭，也稱為EPOCH。 即時(shí)值可以是負(fù)數(shù)舞箍，如果它們在時(shí)代之前發(fā)生舰褪。 它們遵循ISO 8601表示日期和時(shí)間的標(biāo)準(zhǔn)。
// 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
這是另外兩個(gè)非常有用也很重要的類创译。Period主要使用基于date（日期）的值,例如 years, months, days 來代表一段時(shí)間抵知。Duration則是基于秒或者毫秒的。 他們的值可以是負(fù)數(shù)软族，如果結(jié)束時(shí)間發(fā)生在起始時(shí)間之前刷喜。
// 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 對象之間的轉(zhuǎn)換
// 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());
現(xiàn)在來看， 對于時(shí)間跟日期的操作真的是比以往方便了很多立砸，我們可以徹底告別各種蛋疼的邏輯操作了掖疮。
