【Java8新特性】關於Java8中的日期時間API，你需要掌握這些！！

寫在前面

Java8之前的日期和時間API，存在一些問題，比如：執行緒安全的問題，跨年的問題等等。這些問題都在Hava8中的日期和時間API中得到了解決，而且Java8中的日期和時間API更加強大。立志成為架構師的你，必須掌握Java8中的日期和時間API。

本地時間和時間戳

主要方法：

• now：靜態方法，根據當前時間建立物件
• of：靜態方法，根據指定日期/時間建立物件
• plusDays,plusWeeks,plusMonths,plusYears：向當前LocalDate 物件新增幾天、幾周、幾個月、幾年
• minusDays,minusWeeks,minusMonths,minusYears：從當前LocalDate 物件減去幾天、幾周、幾個月、幾年
• plus,minus：新增或減少一個Duration 或Period
• withDayOfMonth,withDayOfYear,withMonth,withYear：將月份天數、年份天數、月份、年份修改為指定的值並返回新的LocalDate 物件
• getDayOfYear：獲得年份天數(1~366)
• getDayOfWeek：獲得星期幾(返回一個DayOfWeek列舉值)
• getMonth：獲得月份, 返回一個Month 列舉值
• getMonthValue：獲得月份(1~12)
• getYear：獲得年份
• until：獲得兩個日期之間的Period 物件，或者指定ChronoUnits 的數字
• isBefore,isAfter：比較兩個LocalDate
• isLeapYear：判斷是否是閏年

使用 LocalDate、 LocalTime、 LocalDateTime

LocalDate、 LocalTime、 LocalDateTime 類的例項是不可變的物件，分別表示使用 ISO-8601日曆系統的日期、時間、日期和時間。它們提供了簡單的日期或時間，並不包含當前的時間資訊。也不包含與時區相關的資訊。

注： ISO-8601日曆系統是國際標準化組織制定的現代公民的日期和時間的表示法

方法	描述	示例
now()	靜態方法，根據當前時間建立物件	LocalDate localDate = LocalDate.now(); LocalTime localTime = LocalTime.now(); LocalDateTime localDateTime = LocalDateTime.now();
of()	靜態方法，根據指定日期/時間建立 物件	LocalDate localDate = LocalDate.of(2016, 10, 26); LocalTime localTime = LocalTime.of(02, 22, 56); LocalDateTime localDateTime = LocalDateTime.of(2016, 10, 26, 12, 10, 55);
plusDays, plusWeeks, plusMonths, plusYears	向當前 LocalDate 物件新增幾天、 幾周、 幾個月、 幾年
minusDays, minusWeeks, minusMonths, minusYears	從當前 LocalDate 物件減去幾天、 幾周、 幾個月、 幾年
plus, minus	新增或減少一個 Duration 或 Period
withDayOfMonth, withDayOfYear, withMonth, withYear	將月份天數、 年份天數、 月份、 年 份 修 改 為 指 定 的 值 並 返 回 新 的 LocalDate 物件
getDayOfMonth	獲得月份天數(1-31)
getDayOfYear	獲得年份天數(1-366)
getDayOfWeek	獲得星期幾(返回一個 DayOfWeek 列舉值)
getMonth	獲得月份, 返回一個 Month 列舉值
getMonthValue	獲得月份(1-12)
getYear	獲得年份
until	獲得兩個日期之間的 Period 物件， 或者指定 ChronoUnits 的數字
isBefore, isAfter	比較兩個 LocalDate
isLeapYear	判斷是否是閏年

示例程式碼如下所示。

// 獲取當前系統時間
LocalDateTime localDateTime1 = LocalDateTime.now();
System.out.println(localDateTime1);
// 執行結果：2019-10-27T13:49:09.483

// 指定日期時間
LocalDateTime localDateTime2 = LocalDateTime.of(2019, 10, 27, 13, 45,10);
System.out.println(localDateTime2);
// 執行結果：2019-10-27T13:45:10

LocalDateTime localDateTime3 = localDateTime1
        // 加三年
        .plusYears(3)
        // 減三個月
        .minusMonths(3);
System.out.println(localDateTime3);
// 執行結果：2022-07-27T13:49:09.483

System.out.println(localDateTime1.getYear());       // 執行結果：2019
System.out.println(localDateTime1.getMonthValue()); // 執行結果：10
System.out.println(localDateTime1.getDayOfMonth()); // 執行結果：27
System.out.println(localDateTime1.getHour());       // 執行結果：13
System.out.println(localDateTime1.getMinute());     // 執行結果：52
System.out.println(localDateTime1.getSecond());     // 執行結果：6

LocalDateTime localDateTime4 = LocalDateTime.now();
System.out.println(localDateTime4);     // 2019-10-27T14:19:56.884
LocalDateTime localDateTime5 = localDateTime4.withDayOfMonth(10);
System.out.println(localDateTime5);     // 2019-10-10T14:19:56.884

Instant 時間戳

用於“時間戳”的運算。它是以Unix元年(傳統的設定為UTC時區1970年1月1日午夜時分)開始所經歷的描述進行運算 。

示例程式碼如下所示。

Instant instant1 = Instant.now();    // 預設獲取UTC時區
System.out.println(instant1);
// 執行結果：2019-10-27T05:59:58.221Z

// 偏移量運算
OffsetDateTime offsetDateTime = instant1.atOffset(ZoneOffset.ofHours(8));
System.out.println(offsetDateTime);
// 執行結果：2019-10-27T13:59:58.221+08:00

// 獲取時間戳
System.out.println(instant1.toEpochMilli());
// 執行結果：1572156145000

// 以Unix元年為起點，進行偏移量運算
Instant instant2 = Instant.ofEpochSecond(60);
System.out.println(instant2);
// 執行結果：1970-01-01T00:01:00Z

Duration 和 Period

Duration:用於計算兩個“時間”間隔。

Period:用於計算兩個“日期”間隔 。

Instant instant_1 = Instant.now();
try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    e.printStackTrace();
}
Instant instant_2 = Instant.now();

Duration duration = Duration.between(instant_1, instant_2);
System.out.println(duration.toMillis());
// 執行結果：1000

LocalTime localTime_1 = LocalTime.now();
try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    e.printStackTrace();
}
LocalTime localTime_2 = LocalTime.now();

System.out.println(Duration.between(localTime_1, localTime_2).toMillis());
// 執行結果：1000

LocalDate localDate_1 = LocalDate.of(2018,9, 9);
LocalDate localDate_2 = LocalDate.now();

Period period = Period.between(localDate_1, localDate_2);
System.out.println(period.getYears());      // 執行結果：1
System.out.println(period.getMonths());     // 執行結果：1
System.out.println(period.getDays());       // 執行結果：18

日期的操縱

TemporalAdjuster : 時間校正器。有時我們可能需要獲取例如：將日期調整到“下個週日”等操作。

TemporalAdjusters : 該類通過靜態方法提供了大量的常用 TemporalAdjuster 的實現。

例如獲取下個週日，如下所示：

LocalDate nextSunday = LocalDate.now().with(TemporalAdjusters.next(DayOfWeek.SUNDAY));

完整的示例程式碼如下所示。

LocalDateTime localDateTime1 = LocalDateTime.now();
System.out.println(localDateTime1);     // 2019-10-27T14:19:56.884

// 獲取這個第一天的日期
System.out.println(localDateTime1.with(TemporalAdjusters.firstDayOfMonth()));            // 2019-10-01T14:22:58.574
// 獲取下個週末的日期
System.out.println(localDateTime1.with(TemporalAdjusters.next(DayOfWeek.SUNDAY)));       // 2019-11-03T14:22:58.574

// 自定義：下一個工作日
LocalDateTime localDateTime2 = localDateTime1.with(l -> {
    LocalDateTime localDateTime = (LocalDateTime) l;
    DayOfWeek dayOfWeek =  localDateTime.getDayOfWeek();

    if (dayOfWeek.equals(DayOfWeek.FRIDAY)) {
       return localDateTime.plusDays(3);
    } else if (dayOfWeek.equals(DayOfWeek.SATURDAY)) {
       return localDateTime.plusDays(2);
    } else {
       return localDateTime.plusDays(1);
    }
});
System.out.println(localDateTime2);
// 執行結果：2019-10-28T14:30:17.400

解析與格式化

java.time.format.DateTimeFormatter 類：該類提供了三種格式化方法：

• 預定義的標準格式
• 語言環境相關的格式
• 自定義的格式

示例程式碼如下所示。

DateTimeFormatter dateTimeFormatter1 = DateTimeFormatter.ISO_DATE;
LocalDateTime localDateTime = LocalDateTime.now();
String strDate1 = localDateTime.format(dateTimeFormatter1);
System.out.println(strDate1);
// 執行結果：2019-10-27

// Date -> String
DateTimeFormatter dateTimeFormatter2 = DateTimeFormatter.ofPattern("yyyy-MM-dd  HH:mm:ss");
String strDate2 = dateTimeFormatter2.format(localDateTime);
System.out.println(strDate2);
// 執行結果：2019-10-27  14:36:11

// String -> Date
LocalDateTime localDateTime1 = localDateTime.parse(strDate2, dateTimeFormatter2);
System.out.println(localDateTime1);
// 執行結果：2019-10-27T14:37:39

時區的處理

Java8 中加入了對時區的支援，帶時區的時間為分別為：ZonedDate、 ZonedTime、 ZonedDateTime。

其中每個時區都對應著 ID，地區ID都為 “{區域}/{城市}”的格式，例如 ： Asia/Shanghai 等。

• ZoneId：該類中包含了所有的時區資訊
• getAvailableZoneIds() : 可以獲取所有時區時區資訊
• of(id) : 用指定的時區資訊獲取 ZoneId 物件

示例程式碼如下所示。

// 獲取所有的時區
Set<String> set = ZoneId.getAvailableZoneIds();
System.out.println(set);
// [Asia/Aden, America/Cuiaba, Etc/GMT+9, Etc/GMT+8, Africa/Nairobi, America/Marigot, Asia/Aqtau, Pacific/Kwajalein, America/El_Salvador, Asia/Pontianak, Africa/Cairo, Pacific/Pago_Pago, Africa/Mbabane, Asia/Kuching, Pacific/Honolulu, Pacific/Rarotonga, America/Guatemala, Australia/Hobart, Europe/London, America/Belize, America/Panama, Asia/Chungking, America/Managua, America/Indiana/Petersburg, Asia/Yerevan, Europe/Brussels, GMT, Europe/Warsaw, America/Chicago, Asia/Kashgar, Chile/Continental, Pacific/Yap, CET, Etc/GMT-1, Etc/GMT-0, Europe/Jersey, America/Tegucigalpa, Etc/GMT-5, Europe/Istanbul, America/Eirunepe, Etc/GMT-4, America/Miquelon, Etc/GMT-3, Europe/Luxembourg, Etc/GMT-2, Etc/GMT-9, America/Argentina/Catamarca, Etc/GMT-8, Etc/GMT-7, Etc/GMT-6, Europe/Zaporozhye, Canada/Yukon, Canada/Atlantic, Atlantic/St_Helena, Australia/Tasmania, Libya, Europe/Guernsey, America/Grand_Turk, US/Pacific-New, Asia/Samarkand, America/Argentina/Cordoba, Asia/Phnom_Penh, Africa/Kigali, Asia/Almaty, US/Alaska, Asia/Dubai, Europe/Isle_of_Man, America/Araguaina, Cuba, Asia/Novosibirsk, America/Argentina/Salta, Etc/GMT+3, Africa/Tunis, Etc/GMT+2, Etc/GMT+1, Pacific/Fakaofo, Africa/Tripoli, Etc/GMT+0, Israel, Africa/Banjul, Etc/GMT+7, Indian/Comoro, Etc/GMT+6, Etc/GMT+5, Etc/GMT+4, Pacific/Port_Moresby, US/Arizona, Antarctica/Syowa, Indian/Reunion, Pacific/Palau, Europe/Kaliningrad, America/Montevideo, Africa/Windhoek, Asia/Karachi, Africa/Mogadishu, Australia/Perth, Brazil/East, Etc/GMT, Asia/Chita, Pacific/Easter, Antarctica/Davis, Antarctica/McMurdo, Asia/Macao, America/Manaus, Africa/Freetown, Europe/Bucharest, Asia/Tomsk, America/Argentina/Mendoza, Asia/Macau, Europe/Malta, Mexico/BajaSur, Pacific/Tahiti, Africa/Asmera, Europe/Busingen, America/Argentina/Rio_Gallegos, Africa/Malabo, Europe/Skopje, America/Catamarca, America/Godthab, Europe/Sarajevo, Australia/ACT, GB-Eire, Africa/Lagos, America/Cordoba, Europe/Rome, Asia/Dacca, Indian/Mauritius, Pacific/Samoa, America/Regina, America/Fort_Wayne, America/Dawson_Creek, Africa/Algiers, Europe/Mariehamn, America/St_Johns, America/St_Thomas, Europe/Zurich, America/Anguilla, Asia/Dili, America/Denver, Africa/Bamako, Europe/Saratov, GB, Mexico/General, Pacific/Wallis, Europe/Gibraltar, Africa/Conakry, Africa/Lubumbashi, Asia/Istanbul, America/Havana, NZ-CHAT, Asia/Choibalsan, America/Porto_Acre, Asia/Omsk, Europe/Vaduz, US/Michigan, Asia/Dhaka, America/Barbados, Europe/Tiraspol, Atlantic/Cape_Verde, Asia/Yekaterinburg, America/Louisville, Pacific/Johnston, Pacific/Chatham, Europe/Ljubljana, America/Sao_Paulo, Asia/Jayapura, America/Curacao, Asia/Dushanbe, America/Guyana, America/Guayaquil, America/Martinique, Portugal, Europe/Berlin, Europe/Moscow, Europe/Chisinau, America/Puerto_Rico, America/Rankin_Inlet, Pacific/Ponape, Europe/Stockholm, Europe/Budapest, America/Argentina/Jujuy, Australia/Eucla, Asia/Shanghai, Universal, Europe/Zagreb, America/Port_of_Spain, Europe/Helsinki, Asia/Beirut, Asia/Tel_Aviv, Pacific/Bougainville, US/Central, Africa/Sao_Tome, Indian/Chagos, America/Cayenne, Asia/Yakutsk, Pacific/Galapagos, Australia/North, Europe/Paris, Africa/Ndjamena, Pacific/Fiji, America/Rainy_River, Indian/Maldives, Australia/Yancowinna, SystemV/AST4, Asia/Oral, America/Yellowknife, Pacific/Enderbury, America/Juneau, Australia/Victoria, America/Indiana/Vevay, Asia/Tashkent, Asia/Jakarta, Africa/Ceuta, Asia/Barnaul, America/Recife, America/Buenos_Aires, America/Noronha, America/Swift_Current, Australia/Adelaide, America/Metlakatla, Africa/Djibouti, America/Paramaribo, Europe/Simferopol, Europe/Sofia, Africa/Nouakchott, Europe/Prague, America/Indiana/Vincennes, Antarctica/Mawson, America/Kralendijk, Antarctica/Troll, Europe/Samara, Indian/Christmas, America/Antigua, Pacific/Gambier, America/Indianapolis, America/Inuvik, America/Iqaluit, Pacific/Funafuti, UTC, Antarctica/Macquarie, Canada/Pacific, America/Moncton, Africa/Gaborone, Pacific/Chuuk, Asia/Pyongyang, America/St_Vincent, Asia/Gaza, Etc/Universal, PST8PDT, Atlantic/Faeroe, Asia/Qyzylorda, Canada/Newfoundland, America/Kentucky/Louisville, America/Yakutat, Asia/Ho_Chi_Minh, Antarctica/Casey, Europe/Copenhagen, Africa/Asmara, Atlantic/Azores, Europe/Vienna, ROK, Pacific/Pitcairn, America/Mazatlan, Australia/Queensland, Pacific/Nauru, Europe/Tirane, Asia/Kolkata, SystemV/MST7, Australia/Canberra, MET, Australia/Broken_Hill, Europe/Riga, America/Dominica, Africa/Abidjan, America/Mendoza, America/Santarem, Kwajalein, America/Asuncion, Asia/Ulan_Bator, NZ, America/Boise, Australia/Currie, EST5EDT, Pacific/Guam, Pacific/Wake, Atlantic/Bermuda, America/Costa_Rica, America/Dawson, Asia/Chongqing, Eire, Europe/Amsterdam, America/Indiana/Knox, America/North_Dakota/Beulah, Africa/Accra, Atlantic/Faroe, Mexico/BajaNorte, America/Maceio, Etc/UCT, Pacific/Apia, GMT0, America/Atka, Pacific/Niue, Australia/Lord_Howe, Europe/Dublin, Pacific/Truk, MST7MDT, America/Monterrey, America/Nassau, America/Jamaica, Asia/Bishkek, America/Atikokan, Atlantic/Stanley, Australia/NSW, US/Hawaii, SystemV/CST6, Indian/Mahe, Asia/Aqtobe, America/Sitka, Asia/Vladivostok, Africa/Libreville, Africa/Maputo, Zulu, America/Kentucky/Monticello, Africa/El_Aaiun, Africa/Ouagadougou, America/Coral_Harbour, Pacific/Marquesas, Brazil/West, America/Aruba, America/North_Dakota/Center, America/Cayman, Asia/Ulaanbaatar, Asia/Baghdad, Europe/San_Marino, America/Indiana/Tell_City, America/Tijuana, Pacific/Saipan, SystemV/YST9, Africa/Douala, America/Chihuahua, America/Ojinaga, Asia/Hovd, America/Anchorage, Chile/EasterIsland, America/Halifax, Antarctica/Rothera, America/Indiana/Indianapolis, US/Mountain, Asia/Damascus, America/Argentina/San_Luis, America/Santiago, Asia/Baku, America/Argentina/Ushuaia, Atlantic/Reykjavik, Africa/Brazzaville, Africa/Porto-Novo, America/La_Paz, Antarctica/DumontDUrville, Asia/Taipei, Antarctica/South_Pole, Asia/Manila, Asia/Bangkok, Africa/Dar_es_Salaam, Poland, Atlantic/Madeira, Antarctica/Palmer, America/Thunder_Bay, Africa/Addis_Ababa, Asia/Yangon, Europe/Uzhgorod, Brazil/DeNoronha, Asia/Ashkhabad, Etc/Zulu, America/Indiana/Marengo, America/Creston, America/Punta_Arenas, America/Mexico_City, Antarctica/Vostok, Asia/Jerusalem, Europe/Andorra, US/Samoa, PRC, Asia/Vientiane, Pacific/Kiritimati, America/Matamoros, America/Blanc-Sablon, Asia/Riyadh, Iceland, Pacific/Pohnpei, Asia/Ujung_Pandang, Atlantic/South_Georgia, Europe/Lisbon, Asia/Harbin, Europe/Oslo, Asia/Novokuznetsk, CST6CDT, Atlantic/Canary, America/Knox_IN, Asia/Kuwait, SystemV/HST10, Pacific/Efate, Africa/Lome, America/Bogota, America/Menominee, America/Adak, Pacific/Norfolk, Europe/Kirov, America/Resolute, Pacific/Tarawa, Africa/Kampala, Asia/Krasnoyarsk, Greenwich, SystemV/EST5, America/Edmonton, Europe/Podgorica, Australia/South, Canada/Central, Africa/Bujumbura, America/Santo_Domingo, US/Eastern, Europe/Minsk, Pacific/Auckland, Africa/Casablanca, America/Glace_Bay, Canada/Eastern, Asia/Qatar, Europe/Kiev, Singapore, Asia/Magadan, SystemV/PST8, America/Port-au-Prince, Europe/Belfast, America/St_Barthelemy, Asia/Ashgabat, Africa/Luanda, America/Nipigon, Atlantic/Jan_Mayen, Brazil/Acre, Asia/Muscat, Asia/Bahrain, Europe/Vilnius, America/Fortaleza, Etc/GMT0, US/East-Indiana, America/Hermosillo, America/Cancun, Africa/Maseru, Pacific/Kosrae, Africa/Kinshasa, Asia/Kathmandu, Asia/Seoul, Australia/Sydney, America/Lima, Australia/LHI, America/St_Lucia, Europe/Madrid, America/Bahia_Banderas, America/Montserrat, Asia/Brunei, America/Santa_Isabel, Canada/Mountain, America/Cambridge_Bay, Asia/Colombo, Australia/West, Indian/Antananarivo, Australia/Brisbane, Indian/Mayotte, US/Indiana-Starke, Asia/Urumqi, US/Aleutian, Europe/Volgograd, America/Lower_Princes, America/Vancouver, Africa/Blantyre, America/Rio_Branco, America/Danmarkshavn, America/Detroit, America/Thule, Africa/Lusaka, Asia/Hong_Kong, Iran, America/Argentina/La_Rioja, Africa/Dakar, SystemV/CST6CDT, America/Tortola, America/Porto_Velho, Asia/Sakhalin, Etc/GMT+10, America/Scoresbysund, Asia/Kamchatka, Asia/Thimbu, Africa/Harare, Etc/GMT+12, Etc/GMT+11, Navajo, America/Nome, Europe/Tallinn, Turkey, Africa/Khartoum, Africa/Johannesburg, Africa/Bangui, Europe/Belgrade, Jamaica, Africa/Bissau, Asia/Tehran, WET, Europe/Astrakhan, Africa/Juba, America/Campo_Grande, America/Belem, Etc/Greenwich, Asia/Saigon, America/Ensenada, Pacific/Midway, America/Jujuy, Africa/Timbuktu, America/Bahia, America/Goose_Bay, America/Virgin, America/Pangnirtung, Asia/Katmandu, America/Phoenix, Africa/Niamey, America/Whitehorse, Pacific/Noumea, Asia/Tbilisi, America/Montreal, Asia/Makassar, America/Argentina/San_Juan, Hongkong, UCT, Asia/Nicosia, America/Indiana/Winamac, SystemV/MST7MDT, America/Argentina/ComodRivadavia, America/Boa_Vista, America/Grenada, Asia/Atyrau, Australia/Darwin, Asia/Khandyga, Asia/Kuala_Lumpur, Asia/Famagusta, Asia/Thimphu, Asia/Rangoon, Europe/Bratislava, Asia/Calcutta, America/Argentina/Tucuman, Asia/Kabul, Indian/Cocos, Japan, Pacific/Tongatapu, America/New_York, Etc/GMT-12, Etc/GMT-11, Etc/GMT-10, SystemV/YST9YDT, Europe/Ulyanovsk, Etc/GMT-14, Etc/GMT-13, W-SU, America/Merida, EET, America/Rosario, Canada/Saskatchewan, America/St_Kitts, Arctic/Longyearbyen, America/Fort_Nelson, America/Caracas, America/Guadeloupe, Asia/Hebron, Indian/Kerguelen, SystemV/PST8PDT, Africa/Monrovia, Asia/Ust-Nera, Egypt, Asia/Srednekolymsk, America/North_Dakota/New_Salem, Asia/Anadyr, Australia/Melbourne, Asia/Irkutsk, America/Shiprock, America/Winnipeg, Europe/Vatican, Asia/Amman, Etc/UTC, SystemV/AST4ADT, Asia/Tokyo, America/Toronto, Asia/Singapore, Australia/Lindeman, America/Los_Angeles, SystemV/EST5EDT, Pacific/Majuro, America/Argentina/Buenos_Aires, Europe/Nicosia, Pacific/Guadalcanal, Europe/Athens, US/Pacific, Europe/Monaco]

// 通過時區構建LocalDateTime
LocalDateTime localDateTime1 = LocalDateTime.now(ZoneId.of("America/El_Salvador"));
System.out.println(localDateTime1);
// 2019-10-27T00:46:21.268

// 以時區格式顯示時間
LocalDateTime localDateTime2 = LocalDateTime.now();
ZonedDateTime zonedDateTime1 = localDateTime2.atZone(ZoneId.of("Africa/Nairobi"));
System.out.println(zonedDateTime1);
// 2019-10-27T14:46:21.273+03:00[Africa/Nairobi]

與傳統日期處理的轉換

寫在最後

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