Java 8 日期和時間的API

weixin_33751566發表於2018-07-31
JavaAPI

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執行緒安全的，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。

  • Instant——它代表的是時間戳

  • LocalDate——不包含具體時間的日期，比如2014-01-14。它可以用來儲存生日，週年紀念日，入職日期等。

  • LocalTime——它代表的是不含日期的時間

  • LocalDateTime——它包含了日期及時間，不過還是沒有偏移資訊或者說時區。

  • ZonedDateTime——這是一個包含時區的完整的日期時間，偏移量是以UTC/格林威治時間為基準的。

java.time.chrono包：

這個包為非ISO的日曆系統定義了一些泛化的API，我們可以擴充套件AbstractChronology類來建立自己的日曆系統。

java.time.format包：

這個包包含能夠格式化和解析日期時間物件的類，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。

java.time.temporal包：

這個包包含一些時態物件，我們可以用其找出關於日期/時間物件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後一天。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。

java.time.zone包：

這個包包含支援不同時區以及相關規則的類。

java8處理時間及日期

1.LocalDate

LocalDate是一個不可變的類，它表示預設格式(yyyy-MM-dd)的日期，我們可以使用now()方法得到當前時間，也可以提供輸入年份、月份和日期的輸入引數來建立一個LocalDate例項。該類為now()方法提供了過載方法，我們可以傳入ZoneId來獲得指定時區的日期。該類提供與java.sql.Date相同的功能，對於如何使用該類，我們來看一個簡單的例子。

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);

        //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);
    }
 
}

//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=2014-04-1

2.LocalTime

LocalTime是一個不可變的類，它的例項代表一個符合人類可讀格式的時間，預設格式是hh:mm:ss.zzz。像LocalDate一樣，該類也提供了時區支援，同時也可以傳入小時、分鐘和秒等輸入引數建立例項，我們來看一個簡單的程式，演示該類的使用方法。

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);
 
        //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);
    }
}

//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

3.LocalDateTime

LocalDateTime是一個不可變的日期-時間物件，它表示一組日期-時間，預設格式是yyyy-MM-dd-HH-mm-ss.zzz。它提供了一個工廠方法，接收LocalDate和LocalTime輸入引數，建立LocalDateTime例項。我們來看一個簡單的例子。

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);
 
        //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);
    }
}

//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

4.Instant

Instant類是用在機器可讀的時間格式上的，它以Unix時間戳的形式儲存日期時間，我們來看一個簡單的程式。

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);
    }
 
}
//輸出
Current Timestamp = 2014-04-28T23:20:08.489Z
Specific Time = 2014-04-28T23:20:08.489Z
PT720H

5.日期API工具

我們早些時候提到過，大多數日期/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。還有其他的工具方法能夠使用TemporalAdjuster調整日期，並計算兩個日期間的週期。

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());        
    }
}
//輸出
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

6.解析和格式化

public class GetDate {

    public final static String YYYYMMDD = "yyyy-MM-dd";
    public final static String YEAR_MONTH_DAY = "yyyy年MM月dd日";
    public final static String YYYYMMDDHHMMSS = "yyyy-MM-dd HH:mm:ss";
    public final static String YYYYMMDDHHMMSSSSS = "yyyyMMddHHmmssSSS";
    public final static String YYYYMMDDHHMMSS_NOSIGN = "yyyyMMddHHmmss";
    public final static String YYYYMMDD_1 = "yyyyMMdd";


    // ---------------------------- Formatter ---------------------------

    /**
     * 2018-05-31
     */
    public final static DateTimeFormatter FORMATTER_LOCAL = DateTimeFormatter.ISO_LOCAL_DATE;

    /**
     * 2018年05月31日
     */
    public final static DateTimeFormatter FORMATTER_YEAR_MONTH_DAY = DateTimeFormatter.ofPattern(YEAR_MONTH_DAY);

    /**
     * 2018-05-31 11:12:42
     */
    public final static DateTimeFormatter FORMATTER_YYYYMMDDHHMMSS = DateTimeFormatter.ofPattern(YYYYMMDDHHMMSS);

    /**
     * 20180531110806694
     */
    public final static DateTimeFormatter FORMATTER_YYYYMMDDHHMMSSSSS = DateTimeFormatter.ofPattern(YYYYMMDDHHMMSSSSS);

    /**
     * 20180629173455
     */
    public final static DateTimeFormatter FORMATTER_YYYYMMDDHHMMSS_NOSIGN = DateTimeFormatter.ofPattern(YYYYMMDDHHMMSS_NOSIGN);

    /**
     * 2018-05-31
     */
    public final static DateTimeFormatter FORMATTER_YYYYMMDD = DateTimeFormatter.ofPattern(YYYYMMDD);

    public final static DateTimeFormatter FORMATTER_YYYYMMDD_1 = DateTimeFormatter.ofPattern(YYYYMMDD_1);

    /**
     * 獲取當前時間，並格式化成給定格式
     *
     * @param formatter
     * @return
     */
    public static String getNowTimeString(DateTimeFormatter formatter) {
        LocalDateTime now = LocalDateTime.now();
        return now.format(formatter);
    }

    /**
     * 獲取當前時間Unix格式 (10位int)
     *
     * @return
     */
    public static Integer getNowTimeUnix() {
        LocalDateTime now = LocalDateTime.now();
        return (int) now.toEpochSecond(ZoneOffset.of("+8"));
    }

    /**
     * Unix時間戳格式化成String
     *
     * @param unixTime
     * @param formatter
     * @return
     */
    public static String unixToString(int unixTime, DateTimeFormatter formatter) {
        Instant instant = Instant.ofEpochSecond(unixTime);
        LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, ZoneOffset.of("+8"));
        return localDateTime.format(formatter);
    }

    /**
     * String格式時間轉換成Unix時間戳
     *
     * @param timeStr   "yyyy-MM-dd HH:mm:ss" 這種格式
     * @param formatter
     * @return
     */
    public static int stringToUnix(String timeStr) {
        if (timeStr.length() == 10) {
            timeStr = timeStr + " 00:00:00";
        }
        LocalDateTime localDateTime = LocalDateTime.parse(timeStr, FORMATTER_YYYYMMDDHHMMSS);
        return (int) localDateTime.toEpochSecond(ZoneOffset.of("+8"));
    }

    /**
     * String格式時間轉換成Unix時間戳
     *
     * @param timeStr   "yyyy-MM-dd" 這種格式
     * @param formatter
     * @return
     */
    public static int stringToUnix(String timeStr, DateTimeFormatter formatter) {
        if (timeStr.length() == 10) {
            timeStr = timeStr + " 00:00:00";
        }
        LocalDateTime localDateTime = LocalDateTime.parse(timeStr, FORMATTER_YYYYMMDDHHMMSS);
        return (int) localDateTime.toEpochSecond(ZoneOffset.of("+8"));
    }

    /**
     * 獲得時間開始 例：傳入 2015-12-03 返回 2015-12-03 00:00:00
     *
     * @param curDate
     * @return
     */
    public static String getDayStart(String curDate) {
        return curDate + " 00:00:00";
    }

    /**
     * 獲得時間結束 例：傳入 2015-12-03 返回 2015-12-03 23:59:59
     *
     * @param curDate
     * @return
     */
    public static String getDayEnd(String curDate) {
        return curDate + " 23:59:59";
    }

    /**
     * 獲取秒值
     *
     * @return
     */
    public static Integer getMyTimeInMillis() {
        // 當前時間
        long milliseconds = LocalDateTime.now().toInstant(ZoneOffset.of("+8")).toEpochMilli() / 1000;
        return (int) milliseconds;
    }


    /**
     *  時間戳 去掉時分秒
     * @param unixTime
     * @return
     */
   public static Integer getYYYYMMDDUnix(Integer unixTime){
       Instant instant = Instant.ofEpochSecond(unixTime);
       LocalDateTime localDateTime = LocalDateTime.ofInstant(instant, ZoneOffset.of("+8"));
        return GetDate.stringToUnix(localDateTime.format(GetDate.FORMATTER_YYYYMMDD));
    }
}

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