[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 - 28 Specific Date= 2014 - 01 - 01 Current Date in IST= 2014 - 04 - 29 365th day from base date= 1971 - 01 - 01 100th 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 : 45.240 Specific Time of Day= 12 : 20 : 25.000000040 Current Time in IST= 04 : 21 : 45.276 10000th 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 : 49.455 Current DateTime= 2014 - 04 -28T16: 00 : 49.493 Specific Date= 2014 - 01 -01T10: 10 : 30 Current Date in IST= 2014 - 04 -29T04: 30 : 49.493 10000th 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 .489Z Specific Time = 2014 - 04 -28T23: 20 : 08 .489Z PT720H |
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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? false Today is before 01 / 01 / 2015 ? true Current Time= 2014 - 04 -28T16: 23 : 53.154 10 days after today will be 2014 - 05 - 08 3 weeks after today will be 2014 - 05 - 19 20 months after today will be 2015 - 12 - 28 10 days before today will be 2014 - 04 - 18 3 weeks before today will be 2014 - 04 - 07 20 months before today will be 2012 - 08 - 28 First date of this month= 2014 - 04 - 01 Last date of this year= 2014 - 12 - 31 Period Format= P8M3D Months 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 - 28 28 ::Apr:: 2014 20140428 Default format of LocalDateTime= 2014 - 04 -28T16: 25 : 49.341 28 ::Apr:: 2014 16 :: 25 :: 49 20140428 Default format of Instant= 2014 - 04 -28T23: 25 : 49 .342Z Default 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 : 54.340 2014 - 04 -28T23: 28 : 54 .395Z America/Los_Angeles 2014 - 04 -28T16: 28 : 54.404 - 07 : 00 [America/Los_Angeles] Mon Apr 28 16 : 28 : 54 PDT 2014 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 ]] 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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