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1. Java的日期/時間類的定義并不一致，在java.util和java.sql的包中都有日期類，此外用于格式化和解析的類在java.text包中定義。
2. java.util.Date同時包含日期和時間，而java.sql.Date僅包含日期，將其納入java.sql包并不合理。另外這兩個類都有相同的名字，這本身就是一個非常糟糕的設計。
3. 對于時間、時間戳、格式化以及解析，并沒有一些明確定義的類。對于格式化和解析的需求，我們有java.text.DateFormat抽象類，但通常情況下，SimpleDateFormat類被用于此類需求。
4. 所有的日期類都是可變的，因此他們都不是線程安全的，這是Java日期類最大的問題之一。
5. 日期類并不提供國際化，沒有時區支持，因此Java引入了java.util.Calendar和java.util.TimeZone類，但他們同樣存在上述所有的問題。

1. 不變性：新的日期/時間API中，所有的類都是不可變的，這對多線程環境有好處。
2. 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，它為日期（Date）、時間（Time）、日期時間（DateTime）、時間戳（unix timestamp）以及時區定義了不同的類。
3. 清晰：在所有的類中，方法都被明確定義用以完成相同的行為。舉個例子，要拿到當前實例我們可以使用now()方法，在所有的類中都定義了format()和parse()方法，而不是像以前那樣專門有一個獨立的類。為了更好的處理問題，所有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，與其他類協同工作并不困難。
4. 實用操作：所有新的日期/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。
5. 可擴展性：新的日期/時間API是工作在ISO-8601日歷系統上的，但我們也可以將其應用在非IOS的日歷上。

1. java.time包：這是新的Java日期/時間API的基礎包，所有的主要基礎類都是這個包的一部分，如：LocalDate, LocalTime, LocalDateTime, Instant, Period, Duration等等。所有這些類都是不可變的和線程安全的，在絕大多數情況下，這些類能夠有效地處理一些公共的需求。
2. java.time.chrono包：這個包為非ISO的日歷系統定義了一些泛化的API，我們可以擴展AbstractChronology類來創建自己的日歷系統。
3. java.time.format包：這個包包含能夠格式化和解析日期時間對象的類，在絕大多數情況下，我們不應該直接使用它們，因為java.time包中相應的類已經提供了格式化和解析的方法。
4. java.time.temporal包：這個包包含一些時態對象，我們可以用其找出關于日期/時間對象的某個特定日期或時間，比如說，可以找到某月的第一天或最后一天。你可以非常容易地認出這些方法，因為它們都具有“withXXX”的格式。
5. java.time.zone包：這個包包含支持不同時區以及相關規則的類。

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);    }}

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

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);    }}

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

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);    }}

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

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;">上述程序的輸出是：</span>

Current Timestamp = 2014-04-28T23:20:08.489ZSpecific Time = 2014-04-28T23:20:08.489ZPT720H

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());            }}

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

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，可以看到如下輸出。

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

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);    }}

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]