TimeZone, ZonedDateTime, Calendar, DateFormat

time.kt

// java 8 이상에서 현재 시간에 맞는 각 타임존 별 시간 얻기
  val pattern = DateTimeFormatter.ofPattern("HH:mm:ss")

  val seoul = ZonedDateTime.now()
  println(seoul.format(pattern))

  val utc = seoul.withZoneSameInstant(ZoneOffset.UTC)
  println(utc.format(pattern))

  val vancouver = utc.withZoneSameInstant(ZoneId.of("America/Vancouver"))
  println(vancouver.format(pattern))

  println("==========================================================")
  // 타임존 별 시간 얻어오기

  val dateFormat = SimpleDateFormat("HH:mm:ss")
  val calendar = Calendar.getInstance()

  val seoulTimeZone = TimeZone.getDefault()
  calendar.timeZone = seoulTimeZone
  val seoulTime = dateFormat.format(calendar.time)
  println(seoulTime)

  val utcTimeZone = TimeZone.getTimeZone("UTC")
  calendar.timeZone = utcTimeZone
  dateFormat.timeZone = utcTimeZone
  val utcTime = dateFormat.format(calendar.time)
  println(utcTime)

  val vancouverTimeZone = TimeZone.getTimeZone("America/Vancouver")
  calendar.timeZone = vancouverTimeZone
  dateFormat.timeZone = vancouverTimeZone
  val vancouverTime = dateFormat.format(calendar.time)
  println(vancouverTime)

  println("==========================================================")
  // calendar 이용해서 특정 시간 각 타임존에 맞는 시간 얻기

  val time = "11:00:00"
  val times = time.split(":")
  calendar.set(Calendar.HOUR_OF_DAY, times[0].toInt())
  calendar.set(Calendar.MINUTE, times[1].toInt())
  calendar.set(Calendar.SECOND, times[2].toInt())
  calendar.timeZone = seoulTimeZone
  dateFormat.timeZone = utcTimeZone

  // expect "02:00:00"
  val timeToUTC = dateFormat.format(calendar.time)
  println(timeToUTC)

  // expect "18:00:00"
  calendar.timeZone = utcTimeZone
  dateFormat.timeZone = vancouverTimeZone
  val timeToVancouver = dateFormat.format(calendar.time)
  println(timeToVancouver)