Dates with babashka

I seldomly do date/time manipulation with babashka and, while working on a recent personal project, I had to look it all up and it took much longer than it should. Ergo, for future reference:

1. Imports:

   (ns mybb
     (:import
      (java.time Instant Duration ZonedDateTime ZoneId)
      (java.time.format DateTimeFormatter)))
   

2. Common defs:

   (def now (Instant/now))
   (def zone-id (ZoneId/systemDefault)) ; => #object[java.time.ZoneRegion 0x71cb68be "Europe/Paris"]
   (def local-date-pattern (DateTimeFormatter/ofPattern "dd/MM/yyyy"))
   (def tz-datetime-pattern (DateTimeFormatter/ofPattern "dd/MM/yyyy HH:mm:ss z"))
   

3. Formatting a date instance as a string:

   (.format local-date-pattern date)
   

4. Get the system zone-id and determine the time-offset.

   (def tz-offset (.getOffset (.getRules zone-id) now)) ; => #object[java.time.ZoneOffset 0x57d84226 "+02:00"]
   (.toString tz-offset) ; => "+02:00"
   

5. Parse a date to create a ZonedDateTime.

   (ZonedDateTime/parse "09/11/2023 12:01:04 +02:00" tz-datetime-pattern) ; => #object[java.time.ZonedDateTime 0x70411fb8 "2023-11-09T12:01:04+02:00"]
   

6. date +/- number of days

   (.minusDays zoned-datetime 10)
   (.plusDays zoned-datetime 10)
   

7. Difference between two date-times, in seconds. NOTE: to convert to instants, you must be using ZonedDateTime.

   (-> (Duration/between (.toInstant zoned-datetime-1)
                         (.toInstant zoned-datetime-2))
       (.getSeconds))
   

Published: 2024-08-19

Tagged: clojure java-time babashka