[转] Java8 日期/时间(Date Time)API指南
[From] http://www.importnew.com/14140.html
Java 8日期/时间( Date/Time)API是开发人员最受追捧的变化之一,Java从一开始就没有对日期时间处理的一致性方法,因此日期/时间API也是除Java核心API以外另一项倍受欢迎的内容。
为什么我们需要新的Java日期/时间API?
- Java的日期/时间类的定义并不一致,在java.util和java.sql的包中都有日期类,此外用于格式化和解析的类在java.text包中定义。
- java.util.Date同时包含日期和时间,而java.sql.Date仅包含日期,将其纳入java.sql包并不合理。另外这两个类都有相同的名字,这本身就是一个非常糟糕的设计。
- 对于时间、时间戳、格式化以及解析,并没有一些明确定义的类。对于格式化和解析的需求,我们有java.text.DateFormat抽象类,但通常情况下,SimpleDateFormat类被用于此类需求。
- 所有的日期类都是可变的,因此他们都不是线程安全的,这是Java日期类最大的问题之一。
- 日期类并不提供国际化,没有时区支持,因此Java引入了java.util.Calendar和java.util.TimeZone类,但他们同样存在上述所有的问题。
Java 8日期/时间API
- 不变性:新的日期/时间API中,所有的类都是不可变的,这对多线程环境有好处。
- 关注点分离:新的API将人可读的日期时间和机器时间(unix timestamp)明确分离,它为日期(Date)、时间(Time)、日期时间(DateTime)、时间戳(unix timestamp)以及时区定义了不同的类。
- 清晰:在所有的类中,方法都被明确定义用以完成相同的行为。举个例子,要拿到当前实例我们可以使用now()方法,在所有的类中都定义了format()和parse()方法,而不是像以前那样专门有一个独立的类。为了更好的处理问题,所有的类都使用了工厂模式和策略模式,一旦你使用了其中某个类的方法,与其他类协同工作并不困难。
- 实用操作:所有新的日期/时间API类都实现了一系列方法用以完成通用的任务,如:加、减、格式化、解析、从日期/时间中提取单独部分,等等。
- 可扩展性:新的日期/时间API是工作在ISO-8601日历系统上的,但我们也可以将其应用在非IOS的日历上。
Java日期/时间API包
- java.time包:这是新的Java日期/时间API的基础包,所有的主要基础类都是这个包的一部分,如:LocalDate, LocalTime, LocalDateTime, Instant, Period, Duration等等。所有这些类都是不可变的和线程安全的,在绝大多数情况下,这些类能够有效地处理一些公共的需求。
- java.time.chrono包:这个包为非ISO的日历系统定义了一些泛化的API,我们可以扩展AbstractChronology类来创建自己的日历系统。
- java.time.format包:这个包包含能够格式化和解析日期时间对象的类,在绝大多数情况下,我们不应该直接使用它们,因为java.time包中相应的类已经提供了格式化和解析的方法。
- java.time.temporal包:这个包包含一些时态对象,我们可以用其找出关于日期/时间对象的某个特定日期或时间,比如说,可以找到某月的第一天或最后一天。你可以非常容易地认出这些方法,因为它们都具有“withXXX”的格式。
- java.time.zone包:这个包包含支持不同时区以及相关规则的类。
Java日期/时间API示例
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package com.journaldev.java8.time;import java.time.LocalDate;import java.time.Month;import java.time.ZoneId;/** * LocalDate Examples * @author pankaj * */public class LocalDateExample { public static void main(String[] args) { //Current Date LocalDate today = LocalDate.now(); System.out.println("Current Date="+today); //Creating LocalDate by providing input arguments LocalDate firstDay_2014 = LocalDate.of(2014, Month.JANUARY, 1); System.out.println("Specific Date="+firstDay_2014); //Try creating date by providing invalid inputs //LocalDate feb29_2014 = LocalDate.of(2014, Month.FEBRUARY, 29); //Exception in thread "main" java.time.DateTimeException: //Invalid date 'February 29' as '2014' is not a leap year //Current date in "Asia/Kolkata", you can get it from ZoneId javadoc LocalDate todayKolkata = LocalDate.now(ZoneId.of("Asia/Kolkata")); System.out.println("Current Date in IST="+todayKolkata); //java.time.zone.ZoneRulesException: Unknown time-zone ID: IST //LocalDate todayIST = LocalDate.now(ZoneId.of("IST")); //Getting date from the base date i.e 01/01/1970 LocalDate dateFromBase = LocalDate.ofEpochDay(365); System.out.println("365th day from base date= "+dateFromBase); LocalDate hundredDay2014 = LocalDate.ofYearDay(2014, 100); System.out.println("100th day of 2014="+hundredDay2014); }} |
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Current Date=2014-04-28Specific Date=2014-01-01Current Date in IST=2014-04-29365th day from base date= 1971-01-01100th day of 2014=2014-04-10 |
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package com.journaldev.java8.time;import java.time.LocalTime;import java.time.ZoneId;/** * LocalTime Examples * @author pankaj * */public class LocalTimeExample { public static void main(String[] args) { //Current Time LocalTime time = LocalTime.now(); System.out.println("Current Time="+time); //Creating LocalTime by providing input arguments LocalTime specificTime = LocalTime.of(12,20,25,40); System.out.println("Specific Time of Day="+specificTime); //Try creating time by providing invalid inputs //LocalTime invalidTime = LocalTime.of(25,20); //Exception in thread "main" java.time.DateTimeException: //Invalid value for HourOfDay (valid values 0 - 23): 25 //Current date in "Asia/Kolkata", you can get it from ZoneId javadoc LocalTime timeKolkata = LocalTime.now(ZoneId.of("Asia/Kolkata")); System.out.println("Current Time in IST="+timeKolkata); //java.time.zone.ZoneRulesException: Unknown time-zone ID: IST //LocalTime todayIST = LocalTime.now(ZoneId.of("IST")); //Getting date from the base date i.e 01/01/1970 LocalTime specificSecondTime = LocalTime.ofSecondOfDay(10000); System.out.println("10000th second time= "+specificSecondTime); }} |
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Current Time=15:51:45.240Specific Time of Day=12:20:25.000000040Current Time in IST=04:21:45.27610000th second time= 02:46:40 |
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package com.journaldev.java8.time;import java.time.LocalDate;import java.time.LocalDateTime;import java.time.LocalTime;import java.time.Month;import java.time.ZoneId;import java.time.ZoneOffset;public class LocalDateTimeExample { public static void main(String[] args) { //Current Date LocalDateTime today = LocalDateTime.now(); System.out.println("Current DateTime="+today); //Current Date using LocalDate and LocalTime today = LocalDateTime.of(LocalDate.now(), LocalTime.now()); System.out.println("Current DateTime="+today); //Creating LocalDateTime by providing input arguments LocalDateTime specificDate = LocalDateTime.of(2014, Month.JANUARY, 1, 10, 10, 30); System.out.println("Specific Date="+specificDate); //Try creating date by providing invalid inputs //LocalDateTime feb29_2014 = LocalDateTime.of(2014, Month.FEBRUARY, 28, 25,1,1); //Exception in thread "main" java.time.DateTimeException: //Invalid value for HourOfDay (valid values 0 - 23): 25 //Current date in "Asia/Kolkata", you can get it from ZoneId javadoc LocalDateTime todayKolkata = LocalDateTime.now(ZoneId.of("Asia/Kolkata")); System.out.println("Current Date in IST="+todayKolkata); //java.time.zone.ZoneRulesException: Unknown time-zone ID: IST //LocalDateTime todayIST = LocalDateTime.now(ZoneId.of("IST")); //Getting date from the base date i.e 01/01/1970 LocalDateTime dateFromBase = LocalDateTime.ofEpochSecond(10000, 0, ZoneOffset.UTC); System.out.println("10000th second time from 01/01/1970= "+dateFromBase); }} |
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Current DateTime=2014-04-28T16:00:49.455Current DateTime=2014-04-28T16:00:49.493Specific Date=2014-01-01T10:10:30Current Date in IST=2014-04-29T04:30:49.49310000th second time from 01/01/1970= 1970-01-01T02:46:40 |
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package com.journaldev.java8.time;import java.time.Duration;import java.time.Instant;public class InstantExample { public static void main(String[] args) { //Current timestamp Instant timestamp = Instant.now(); System.out.println("Current Timestamp = "+timestamp); //Instant from timestamp Instant specificTime = Instant.ofEpochMilli(timestamp.toEpochMilli()); System.out.println("Specific Time = "+specificTime); //Duration example Duration thirtyDay = Duration.ofDays(30); System.out.println(thirtyDay); }} |
<span style="font-family: Georgia, 'Times New Roman', 'Bitstream Charter', Times, serif; font-size: 13px; line-height: 19px;">上述程序的输出是:</span>
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Current Timestamp = 2014-04-28T23:20:08.489ZSpecific Time = 2014-04-28T23:20:08.489ZPT720H |
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package com.journaldev.java8.time;import java.time.LocalDate;import java.time.LocalTime;import java.time.Period;import java.time.temporal.TemporalAdjusters;public class DateAPIUtilities { public static void main(String[] args) { LocalDate today = LocalDate.now(); //Get the Year, check if it's leap year System.out.println("Year "+today.getYear()+" is Leap Year? "+today.isLeapYear()); //Compare two LocalDate for before and after System.out.println("Today is before 01/01/2015? "+today.isBefore(LocalDate.of(2015,1,1))); //Create LocalDateTime from LocalDate System.out.println("Current Time="+today.atTime(LocalTime.now())); //plus and minus operations System.out.println("10 days after today will be "+today.plusDays(10)); System.out.println("3 weeks after today will be "+today.plusWeeks(3)); System.out.println("20 months after today will be "+today.plusMonths(20)); System.out.println("10 days before today will be "+today.minusDays(10)); System.out.println("3 weeks before today will be "+today.minusWeeks(3)); System.out.println("20 months before today will be "+today.minusMonths(20)); //Temporal adjusters for adjusting the dates System.out.println("First date of this month= "+today.with(TemporalAdjusters.firstDayOfMonth())); LocalDate lastDayOfYear = today.with(TemporalAdjusters.lastDayOfYear()); System.out.println("Last date of this year= "+lastDayOfYear); Period period = today.until(lastDayOfYear); System.out.println("Period Format= "+period); System.out.println("Months remaining in the year= "+period.getMonths()); }} |
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Year 2014 is Leap Year? falseToday is before 01/01/2015? trueCurrent Time=2014-04-28T16:23:53.15410 days after today will be 2014-05-083 weeks after today will be 2014-05-1920 months after today will be 2015-12-2810 days before today will be 2014-04-183 weeks before today will be 2014-04-0720 months before today will be 2012-08-28First date of this month= 2014-04-01Last date of this year= 2014-12-31Period Format= P8M3DMonths remaining in the year= 8 |
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package com.journaldev.java8.time;import java.time.Instant;import java.time.LocalDate;import java.time.LocalDateTime;import java.time.format.DateTimeFormatter;public class DateParseFormatExample { public static void main(String[] args) { //Format examples LocalDate date = LocalDate.now(); //default format System.out.println("Default format of LocalDate="+date); //specific format System.out.println(date.format(DateTimeFormatter.ofPattern("d::MMM::uuuu"))); System.out.println(date.format(DateTimeFormatter.BASIC_ISO_DATE)); LocalDateTime dateTime = LocalDateTime.now(); //default format System.out.println("Default format of LocalDateTime="+dateTime); //specific format System.out.println(dateTime.format(DateTimeFormatter.ofPattern("d::MMM::uuuu HH::mm::ss"))); System.out.println(dateTime.format(DateTimeFormatter.BASIC_ISO_DATE)); Instant timestamp = Instant.now(); //default format System.out.println("Default format of Instant="+timestamp); //Parse examples LocalDateTime dt = LocalDateTime.parse("27::Apr::2014 21::39::48", DateTimeFormatter.ofPattern("d::MMM::uuuu HH::mm::ss")); System.out.println("Default format after parsing = "+dt); }} |
当运行以上程序时,可以看到如下输出。
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Default format of LocalDate=2014-04-2828::Apr::201420140428Default format of LocalDateTime=2014-04-28T16:25:49.34128::Apr::2014 16::25::4920140428Default format of Instant=2014-04-28T23:25:49.342ZDefault format after parsing = 2014-04-27T21:39:48 |
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package com.journaldev.java8.time;import java.time.Instant;import java.time.LocalDateTime;import java.time.ZoneId;import java.time.ZonedDateTime;import java.util.Calendar;import java.util.Date;import java.util.GregorianCalendar;import java.util.TimeZone;public class DateAPILegacySupport { public static void main(String[] args) { //Date to Instant Instant timestamp = new Date().toInstant(); //Now we can convert Instant to LocalDateTime or other similar classes LocalDateTime date = LocalDateTime.ofInstant(timestamp, ZoneId.of(ZoneId.SHORT_IDS.get("PST"))); System.out.println("Date = "+date); //Calendar to Instant Instant time = Calendar.getInstance().toInstant(); System.out.println(time); //TimeZone to ZoneId ZoneId defaultZone = TimeZone.getDefault().toZoneId(); System.out.println(defaultZone); //ZonedDateTime from specific Calendar ZonedDateTime gregorianCalendarDateTime = new GregorianCalendar().toZonedDateTime(); System.out.println(gregorianCalendarDateTime); //Date API to Legacy classes Date dt = Date.from(Instant.now()); System.out.println(dt); TimeZone tz = TimeZone.getTimeZone(defaultZone); System.out.println(tz); GregorianCalendar gc = GregorianCalendar.from(gregorianCalendarDateTime); System.out.println(gc); }} |
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Date = 2014-04-28T16:28:54.3402014-04-28T23:28:54.395ZAmerica/Los_Angeles2014-04-28T16:28:54.404-07:00[America/Los_Angeles]Mon Apr 28 16:28:54 PDT 2014sun.util.calendar.ZoneInfo[id="America/Los_Angeles",offset=-28800000,dstSavings=3600000,useDaylight=true,transitions=185,lastRule=java.util.SimpleTimeZone[id=America/Los_Angeles,offset=-28800000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]]java.util.GregorianCalendar[time=1398727734404,areFieldsSet=true,areAllFieldsSet=true,lenient=true,zone=sun.util.calendar.ZoneInfo[id="America/Los_Angeles",offset=-28800000,dstSavings=3600000,useDaylight=true,transitions=185,lastRule=java.util.SimpleTimeZone[id=America/Los_Angeles,offset=-28800000,dstSavings=3600000,useDaylight=true,startYear=0,startMode=3,startMonth=2,startDay=8,startDayOfWeek=1,startTime=7200000,startTimeMode=0,endMode=3,endMonth=10,endDay=1,endDayOfWeek=1,endTime=7200000,endTimeMode=0]],firstDayOfWeek=2,minimalDaysInFirstWeek=4,ERA=1,YEAR=2014,MONTH=3,WEEK_OF_YEAR=18,WEEK_OF_MONTH=5,DAY_OF_MONTH=28,DAY_OF_YEAR=118,DAY_OF_WEEK=2,DAY_OF_WEEK_IN_MONTH=4,AM_PM=1,HOUR=4,HOUR_OF_DAY=16,MINUTE=28,SECOND=54,MILLISECOND=404,ZONE_OFFSET=-28800000,DST_OFFSET=3600000] |
原文链接: journaldev 翻译: ImportNew.com- Justin Wu
译文链接: http://www.importnew.com/14140.html
[ 转载请保留原文出处、译者和译文链接。]
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