Dates and Time

Introduction to Java Interoperability

Use cases for dates and times

• timestamps on log events
• calendars
• tracking work
• calculating time between two date stamps

Java Time available by default

java.time namespace is available on the class path by default, require or import expressions are not required.

Current data time

Create a date and time stamp with the current data and time for the Operating System timezone.

(java.time.LocalDateTime/now)

A Java time object is returned

#object[java.time.LocalDateTime 0xf36f34d "2023-07-13T13:32:22.483261516"]

Current date

(java.time.LocalDate/now)

;; => #object[java.time.LocalDate 0x5814b4fb "2023-07-13"]

Instant

(java.time.Instant/now)
;; => #object[java.time.Instant 0x3684d2c0 "2023-07-13T13:02:27.889805413Z"]

Clojure Spec

use Clojure Spec to define a data structure containing a java.time.LocalDate element

(spec/def :employee/first-name string?)
(spec/def :employee/last-name string?)
(spec/def :employee/birth-date #(instance? java.time.LocalDate %))

(spec/def :employee/person
  (s/keys :req [:employee/first-name
                :employee/last-name
                :employee/birth-date]))

(def jenny #:ex{:first-name "Jenny"
             :last-name  "Barnes"
             :birth-date (java.time.LocalDate/parse "1910-03-15")})

Check to see if Jenny is a valid employee

(s/valid? :employee/person jenny)
;; => true