java time library

java-time.api.md

Duration

(time/duration dur-str)

ZoneId type

(def event-time-zone (java.time.ZoneId/of "Europe/Brussels"))

decided time type

• ZonedDateTime
  • case: 生成

(java.time.ZonedDateTime/ofInstant
     (.toInstant ^java.util.Date value)
     event-time-zone)

• ZonedDateTime
  • case: 取得 hour, minute, time。
  • 取得 day-of-week, day-of-month, month

(let [zone-id (ZoneId/systemDefault)
        zdt (ZonedDateTime/ofInstant instant zone-id)
        day-of-week (.getValue (.getDayOfWeek zdt))
        month (.getMonthValue zdt)
        day-of-month (.getDayOfMonth zdt)
        time (.toLocalTime zdt)]
    {:hour (.getHour time)
     :minute (.getMinute time)
     :day-of-week day-of-week
     :month month
     :day-of-month day-of-month})

• ZonedDateTime
  • case: 取得 minute

(time/truncate-to (time/local-time time) :minutes)

• ZonedDateTime
  • case: 取得 Month and Day

(time/format "dd.MM" time)

• ZonedDateTime
  • case: 取得 week day

(time/day-of-week time)

undecided time type

• LocalDate
• LocalTime
• LocalDateTime

Clojure example

• from String

;; start-date is "2024-08-17"
;; start-time is "09:00"

;; local-date 可以用 String 來初始化
;; local-time 可以用 String 來初始化
;; local-date-time 可以用其它的 time entity 來初始化
### ;; zoned-date-time 可以用 local-date-time 搭配 time zone 來初始化

(let [local-date (time/local-date start-date)
      local-time (time/local-time start-time)
      local-date-time (time/local-date-time local-date local-time)
      start    (time/zoned-date-time local-date-time db/event-time-zone)]
...
)

• From ZonedDateTime

(time/local-date (:session/time session))

Java counterpart

建立日期時間的方式，可以用parse的方式。

val date = LocalDate.parse("2021-01-01")
val time = LocalTime.parse("13:40:50")
val dateTime = LocalDateTime.parse("2021-01-01T13:40:50")

如果要用自定的格式來建立日期時間，就可以使用DateTimeFormatter

val dateTime = LocalDateTime.parse(
  "2021/01/01 13:40:50",
  DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss")
)

clojure.instant (Core library)

• 可以直接 parse 字串，取得 java.util.Date

(use 'clojure.instant)
(read-instant-date "2017-08-23T10:22:22")
;; #inst "2017-08-23T10:22:22.000-00:00"

;; If no timezone info is included in the input string, GMT is assumed.
;; See clojure.instant/parse-timestamp for the timestamp pattern supported.

• 可以直接 parse 字串，取得時間的 vector 表示

(instant/parse-timestamp vector "2020-04-25T15:09:16.437Z")
;; => [2020 4 25 15 9 16 437000000 0 0 0]

java.util.Date 與 Instant 互轉

;; `Instant` 轉換為 `java.util.Date`
(defn instant->date [^java.time.Instant instant]
  (java.util.Date/from instant))

;; `java.util.Date` 轉換回 `Instant`
(defn date->instant [^java.util.Date date]
  (.toInstant date))

java.util.Date 轉換為 LocalDateTime 或 ZonedDateTime

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.util.Date;

Date date = new Date();
LocalDateTime localDateTime = date.toInstant()
                                   .atZone(ZoneId.systemDefault())
                                   .toLocalDateTime(); // Date -> LocalDateTime
System.out.println(localDateTime);