Java 8日期/時間( Date/Time)API是開發人員最受追捧的變化之一,Java從一開始就沒有對日期時間處理的一致性方法,所以日期/時間API也是除Java核心API之外另外一項倍受歡迎的內容。java
在開始研究Java 8日期/時間API以前,讓咱們先來看一下爲何咱們須要這樣一個新的API。在Java中,現有的與日期和時間相關的類存在諸多問題,其中有:sql
在現有的日期和日曆類中定義的方法還存在一些其餘的問題,但以上問題已經很清晰地代表:Java須要一個健壯的日期/時間類。這也是爲何Joda Time在Java日期/時間需求中扮演了高質量替換的重要角色。api
Java 8日期/時間API是JSR-310的實現,它的實現目標是克服舊的日期時間實現中全部的缺陷,新的日期/時間API的一些設計原則是:
不變性:新的日期/時間API中,全部的類都是不可變的,這對多線程環境有好處。安全
關注點分離:新的API將人可讀的日期時間和機器時間(unix timestamp)明確分離,它爲日期(Date)、時間(Time)、日期時間(DateTime)、時間戳(unix timestamp)以及時區定義了不一樣的類。多線程
清晰:在全部的類中,方法都被明肯定義用以完成相同的行爲。舉個例子,要拿到當前實例咱們可使用now()方法,在全部的類中都定義了format()和parse()方法,而不是像之前那樣專門有一個獨立的類。爲了更好的處理問題,全部的類都使用了工廠模式和策略模式,一旦你使用了其中某個類的方法,與其餘類協同工做並不困難。工具
實用操做:全部新的日期/時間API類都實現了一系列方法用以完成通用的任務,如:加、減、格式化、解析、從日期/時間中提取單獨部分,等等。
可擴展性:新的日期/時間API是工做在ISO-8601日曆系統上的,但咱們也能夠將其應用在非IOS的日曆上。this
Java日期/時間API包含如下相應的包。線程
java.time.zone包:這個包包含支持不一樣時區以及相關規則的類。設計
咱們已經瀏覽了Java日期/時間API的大多數重要部分,如今是時候根據示例仔細看一下最重要的一些類了。unix
LocalDate是一個不可變的類,它表示默認格式(yyyy-MM-dd)的日期,咱們可使用now()方法獲得當前時間,也能夠提供輸入年份、月份和日期的輸入參數來建立一個LocalDate實例。該類爲now()方法提供了重載方法,咱們能夠傳入ZoneId來得到指定時區的日期。該類提供與java.sql.Date相同的功能,對於如何使用該類,咱們來看一個簡單的例子。
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); } }
示例方法的詳解都包含在註釋內,當咱們運行程序時,能夠獲得如下輸出:
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
LocalTime是一個不可變的類,它的實例表明一個符合人類可讀格式的時間,默認格式是hh:mm:ss.zzz。像LocalDate同樣,該類也提供了時區支持,同時也能夠傳入小時、分鐘和秒等輸入參數建立實例,咱們來看一個簡單的程序,演示該類的使用方法。
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); } }
當運行以上程序時,能夠看到以下輸出。
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
LocalDateTime是一個不可變的日期-時間對象,它表示一組日期-時間,默認格式是yyyy-MM-dd-HH-mm-ss.zzz。它提供了一個工廠方法,接收LocalDate和LocalTime輸入參數,建立LocalDateTime實例。咱們來看一個簡單的例子。
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); } }
在全部這三個例子中,咱們已經看到若是咱們提供了無效的參數去建立日期/時間,那麼系統會拋出java.time.DateTimeException,這是一種運行時異常,咱們並不須要顯式地捕獲它。
同時咱們也看到,可以經過傳入ZoneId獲得日期/時間數據,你能夠從它的Javadoc中獲得支持的Zoneid的列表,當運行以上類時,能夠獲得如下輸出。
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
Instant類是用在機器可讀的時間格式上的,它以Unix時間戳的形式存儲日期時間,咱們來看一個簡單的程序。
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); } }
上述程序的輸出是:
Current Timestamp = 2014-04-28T23:20:08.489Z Specific Time = 2014-04-28T23:20:08.489Z PT720H
咱們早些時候提到過,大多很多天期/時間API類都實現了一系列工具方法,如:加/減天數、週數、月份數,等等。還有其餘的工具方法可以使用TemporalAdjuster調整日期,並計算兩個日期間的週期。
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()); } }
上述程序的輸出是:
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
將一個日期格式轉換爲不一樣的格式,以後再解析一個字符串,獲得日期時間對象,這些都是很常見的。咱們來看一下簡單的例子。
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); } }
當運行以上程序時,能夠看到以下輸出。
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
舊的日期/時間類已經在幾乎全部的應用程序中使用,所以作到向下兼容是必須的。這也是爲何會有若干工具方法幫助咱們將舊的類轉換爲新的類,反之亦然。咱們來看一下簡單的例子。
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); } }
當運行以上程序時,能夠看到以下輸出。
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]
你能夠看到,舊的TimeZone和GregorianCalendar類的toString()方法太囉嗦了,一點都不友好。
這就是全部的Java 8 日期/時間API的內容,我很是喜歡這個API,它易於使用,同時它採起了某項工做,使類似的方法也易於尋找,雖然從舊的類轉移到新的日期時間類須要消耗必定的時間,但我相信這是值得的。