java8 time api usage examples. / published by https://github.com/dacr/code-examples-manager #0f91fe41-5463-4e0c-96c5-ca6a41b2b1da/8f2ae748adfa567d931791026eabe4fb6e89ff51

java-time.sc

// summary : java8 time api usage examples.
// keywords : scala, scalatest, java8time, iso8601, cheatsheet, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 0f91fe41-5463-4e0c-96c5-ca6a41b2b1da
// created-on : 2020-05-31T21:54:52+02:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : scala-cli $file

// ---------------------
//> using scala  "3.3.0"
//> using dep "org.scalatest::scalatest:3.2.16"
//> using objectWrapper
// ---------------------

import org.scalatest._, flatspec._, matchers._

import java.util.{Date, Locale}
import java.time._
import java.time.format.DateTimeFormatter
import java.time.format.DateTimeFormatter.ISO_DATE_TIME

class Java8TimeTest extends AnyFlatSpec with should.Matchers {
  override def suiteName="Java8TimeTest"

  "java8 time" should "produce ISO-8601 default string format" in {
    val dateString = new Date().toInstant.toString
    info(dateString)
    // regex coming from https://rgxdb.com/r/526K7G5W
    dateString should fullyMatch regex """^(?:[\+-]?\d{4}(?!\d{2}\b))(?:(-?)(?:(?:0[1-9]|1[0-2])(?:\1(?:[12]\d|0[1-9]|3[01]))?|W(?:[0-4]\d|5[0-2])(?:-?[1-7])?|(?:00[1-9]|0[1-9]\d|[12]\d{2}|3(?:[0-5]\d|6[1-6])))(?:[T\s](?:(?:(?:[01]\d|2[0-3])(?:(:?)[0-5]\d)?|24\:?00)(?:[\.,]\d+(?!:))?)?(?:\2[0-5]\d(?:[\.,]\d+)?)?(?:[zZ]|(?:[\+-])(?:[01]\d|2[0-3]):?(?:[0-5]\d)?)?)?)?$"""
  }

  it should "support optional parts in date parsing" in {
    val dateFormatPattern = "yyyy-MM-dd'T'HH:mm:ss[.SSS]X"
    val dateTimeFormatter = DateTimeFormatter.ofPattern(dateFormatPattern)
    OffsetDateTime.parse("2020-10-24T08:56:36Z", dateTimeFormatter)
    OffsetDateTime.parse("2020-10-24T08:56:36.294Z", dateTimeFormatter)
    ZonedDateTime.parse("2020-10-24T08:56:36Z", dateTimeFormatter)
    ZonedDateTime.parse("2020-10-24T08:56:36.294Z", dateTimeFormatter)
    LocalDateTime.parse("2020-10-24T08:56:36Z", dateTimeFormatter)
    LocalDateTime.parse("2020-10-24T08:56:36.294Z", dateTimeFormatter)
  }

  it should "be easy to get current datetime" in {
    def nowOld(): Date = new Date()
    def instantNow(): Instant = Instant.now()
    def now(): OffsetDateTime = OffsetDateTime.now(ZoneId.systemDefault)
    def nowUTC(): OffsetDateTime = OffsetDateTime.now(ZoneOffset.UTC)
    info("nowOld="+nowOld().toString)
    info("instantNow="+instantNow().toString) // ISO-8601 string
    info("now="+now().toString) // ISO-8601 string
    info("nowUTC="+nowUTC().toString) // ISO-8601 string
  }

  it should "unfortunately not be able to basically parse some ISO-8601 timezone format using default parse" ignore {
    info("Hmmm in fact it has been fixed, it was not working in some older releases of the JVM, but OK with java 15")
    Instant.parse("2018-04-05T07:07:10.366Z") // OK
    intercept[Exception] {
      Instant.parse("2018-04-05T07:07:10.366+00:00") // KO
    }
  }

  it should "parse any variant of ISO-8601 timezone using ISO_DATE_TIME DateTimeFormatter" in {
    Instant.from(ISO_DATE_TIME.parse("2018-04-05T07:07:10Z")).toString // OK
    Instant.from(ISO_DATE_TIME.parse("2018-04-05T07:07:10.366Z")).toString // OK
    Instant.from(ISO_DATE_TIME.parse("2018-04-05T07:07:10.366+00:00")).toString // OK
    Instant.from(ISO_DATE_TIME.parse("2018-04-05T07:07:10.729433098Z")).toString // OK
  }

  it should "be easy to compute the distance between two dates" in {
    val first = OffsetDateTime.from(ISO_DATE_TIME.parse("2018-01-01T00:00:00Z"))
    val second = OffsetDateTime.from(ISO_DATE_TIME.parse("2018-01-11T00:00:00Z"))
    val duration = Duration.between(first, second)
    duration.toDays shouldBe 10
  }

  it should "be easy to compute the distance between two instants" in {
    val first = OffsetDateTime.from(ISO_DATE_TIME.parse("2018-01-01T00:00:00Z")).toInstant
    val second = OffsetDateTime.from(ISO_DATE_TIME.parse("2018-01-11T00:00:00Z")).toInstant
    val duration = Duration.between(first, second)
    duration.toDays shouldBe 10
  }

  it should "be easy to convert legacy datetime to java8 datetime and vice versa" in {
    info("An Instant is a moment on the timeline in UTC, a count of nanoseconds since the epoch of the first moment of 1970 UTC")
    val legacyDate = new Date()
    val modernInstant = legacyDate.toInstant
    //val modernDate = modernInstant.atZone(ZoneId.systemDefault())
    val modernDate = modernInstant.atOffset(ZoneOffset.UTC)
    modernDate.toInstant.toEpochMilli shouldBe legacyDate.getTime
  }

  it should "be easy to deal with epoch values" in {
    val instantAtZoneOffset: OffsetDateTime = Instant.ofEpochMilli(0L).atOffset(ZoneOffset.UTC)
    val instantAtZoneId: ZonedDateTime = Instant.ofEpochMilli(0L).atZone(ZoneId.of("UTC"))
    val instantLocal:LocalDateTime = LocalDateTime.ofInstant(Instant.ofEpochMilli(0L), ZoneId.of("UTC"))

    info(s"toStringAtZoneOffset=$instantAtZoneOffset")                         // 1970-01-01T00:00Z
    info(s"toStringAtZoneId=$instantAtZoneId")                                 // 1970-01-01T00:00Z[UTC]
    info(s"toStringLocal=$instantLocal")                                       // 1970-01-01T00:00

    info("formattedAtZoneOffset="+ISO_DATE_TIME.format(instantAtZoneOffset))   // 1970-01-01T00:00Z
    info("formattedAtZoneId="+ISO_DATE_TIME.format(instantAtZoneId))           // 1970-01-01T00:00Z[UTC]
    info("formattedAtZoneLocal="+ISO_DATE_TIME.format(instantLocal))           // 1970-01-01T00:00

    info("convertedToZoneOffset="+ISO_DATE_TIME.format(instantAtZoneOffset))                   // 1970-01-01T00:00:00Z
    info("convertedToZoneOffset="+ISO_DATE_TIME.format(instantAtZoneId.toOffsetDateTime))      // 1970-01-01T00:00:00Z
    info("convertedToZoneOffset="+ISO_DATE_TIME.format(instantLocal.atOffset(ZoneOffset.UTC))) // 1970-01-01T00:00:00Z

    instantAtZoneId.toEpochSecond shouldBe instantAtZoneOffset.toEpochSecond
  }

  it should "be easy to parse a date without timezone" in {
    val datestr = "03/18/2015 07:44:00 PM"
    val dateFormat = DateTimeFormatter.ofPattern("MM/dd/yyyy hh:mm:ss a")
    val result = LocalDateTime.parse(datestr, dateFormat)
    info("when the timezone is unknown, it could be setup in adhoc way")
    info(result.toInstant(ZoneOffset.UTC).toString)
  }

  it should "be possible to parse a date and give the right timezone" in {
    val datestr = "03/18/2015 07:44:00 PM"
    val dateFormat = DateTimeFormatter.ofPattern("MM/dd/yyyy hh:mm:ss a").withZone(ZoneId.of("America/Chicago"))
    val result = ZonedDateTime.parse(datestr, dateFormat)
    info(result.toString)
  }

  it should "parse month name" in {
    intercept[Exception] {
      DateTimeFormatter
        .ofPattern("dd-MMM-yyyy HH:mm")
        .withLocale(Locale.FRENCH) // added as it is mydefault locale
        .parse("24-Jan-2013 15:15")
    }
    DateTimeFormatter.ofPattern("dd-MMM-yyyy HH:mm")
      .withLocale(Locale.ENGLISH) // MANDATORY TO AVOID EXCEPTION
      .withZone(ZoneId.of("Europe/Paris"))  // MANDATORY TO AVOID EXCEPTION
      .parse("24-Jan-2013 15:15")

    val dateFormat =
      DateTimeFormatter
        .ofPattern("dd-MMM-yyyy HH:mm")
        .withLocale(Locale.ENGLISH)
        .withZone(ZoneId.of("Europe/Paris"))
    ZonedDateTime.parse("24-Jan-2013 15:15", dateFormat)
  }

  it should "recognize weekend days" in {
    val weekday1 = Instant.from(ISO_DATE_TIME.parse("2020-03-02T10:42:42.042Z"))
    val weekday2 = Instant.from(ISO_DATE_TIME.parse("2020-03-06T10:42:42.042Z"))
    val weday1 = Instant.from(ISO_DATE_TIME.parse("2020-03-07T10:42:42.042Z"))
    val weday2 = Instant.from(ISO_DATE_TIME.parse("2020-03-08T10:42:42.042Z"))
    def isWeekEnd(instant: Instant):Boolean = { // Classical occidental WE
      val day = instant.atZone(ZoneId.systemDefault()).getDayOfWeek
      day == DayOfWeek.SATURDAY || day == DayOfWeek.SUNDAY
    }
    isWeekEnd(weekday1) shouldBe false
    isWeekEnd(weekday2) shouldBe false
    isWeekEnd(weday1) shouldBe true
    isWeekEnd(weday2) shouldBe true
  }

  it should "be easy to get a DateTime from a LocalDate" in {
    info("but of course only once you've provided some time information")
    val csvLocale = Locale.FRENCH
    val csvDateFormat = DateTimeFormatter.ofPattern("dd/MM/yyyy", csvLocale)
    val dateTime =
      LocalDate
      .parse("22/01/2042", csvDateFormat)
      .atTime(12, 42, 24)
      .atZone(ZoneId.of("UTC"))
      .toOffsetDateTime
    dateTime.toString shouldBe "2042-01-22T12:42:24Z"
  }

}


org.scalatest.tools.Runner.main(Array("-oDF", "-s", classOf[Java8TimeTest].getName))