[JAVA] A memorandum when I investigated how to convert from Epoch Time to Date type in Scala

joda-time

Try using Joda Time instead of the standard java.util.Date class. The Joda Time library has a much better API for date processing.

https://codeday.me/jp/qa/20181217/35055.html

Time operation memo with scala https://blog.shibayu36.org/entry/2015/07/27/093406 JodaOrg/joda-time https://github.com/JodaOrg/joda-time/blob/master/.github/issue_template.md

scala> :paste
// Entering paste mode (ctrl-D to finish)

import org.joda.time.DateTime
val dt = new DateTime(1564441580 * 1000L)
val HH = dt.toString("HH")
val mm = dt.toString("mm")

// Exiting paste mode, now interpreting.

import org.joda.time.DateTime
dt: org.joda.time.DateTime = 2019-07-30T08:06:20.000+09:00
HH: String = 08
mm: String = 06

joda-time -> Java8 Time API

Java SE 8 contains a new date and time library that is the successor to Joda-Time.

https://github.com/JodaOrg/joda-time/blob/master/.github/issue_template.md

Remember this much for Java 8 date and time API for the time being https://qiita.com/tag1216/items/91a471b33f383981bfaa Handle date and time in Java (Java8) https://qiita.com/kurukurupapa@github/items/f55395758eba03d749c9

scala> :paste
// Entering paste mode (ctrl-D to finish)

import java.time.{Instant, ZonedDateTime, ZoneId}
import java.time.format.DateTimeFormatter

val zdt       = ZonedDateTime.ofInstant(Instant.ofEpochSecond(1564441580), ZoneId.of("Asia/Tokyo"))
val HH        = zdt.format(DateTimeFormatter.ofPattern("HH"))
val mm        = zdt.format(DateTimeFormatter.ofPattern("mm"))
val dayOfWeek = zdt.getDayOfWeek.toString.toLowerCase

// Exiting paste mode, now interpreting.

import java.time.{Instant, ZonedDateTime, ZoneId}
import java.time.format.DateTimeFormatter
zdt: java.time.ZonedDateTime = 2019-07-30T08:06:20+09:00[Asia/Tokyo]
HH: String = 08
mm: String = 06
dayOfWeek: String = tuesday

toString -> getDisplayName

Defining Show may seem silly, as Scala already has a toString in Any. Any means anything, and you lose type safety. toString may be garbage written by some parent class:

http://eed3si9n.com/herding-cats/ja/Show.html

Enumeration DayOfWeek https://docs.oracle.com/javase/jp/8/docs/api/java/time/DayOfWeek.html

scala> :paste
// Entering paste mode (ctrl-D to finish)

import java.time.{Instant, ZonedDateTime, ZoneId}
import java.time.format.{DateTimeFormatter, TextStyle}
import java.util.Locale

val zdt       = ZonedDateTime.ofInstant(Instant.ofEpochSecond(1564441580), ZoneId.of("Asia/Tokyo"))
val dayOfWeek = zdt.getDayOfWeek.getDisplayName(TextStyle.FULL, Locale.US).toLowerCase

// Exiting paste mode, now interpreting.

import java.time.{Instant, ZonedDateTime, ZoneId}
import java.time.format.{DateTimeFormatter, TextStyle}
import java.util.Locale
zdt: java.time.ZonedDateTime = 2019-07-30T08:06:20+09:00[Asia/Tokyo]
dayOfWeek: String = tuesday