How to convert date format to UTC in Scala?-CodePudding

How to convert date format "2021-02-28 13:38:00.597 0000" to "Mon, Feb 28,2021 15:25:00 UTC" UTC format in Scala?

CodePudding user response：

If you are using an older Java version prior to Java 8, it's best to use the DateTimeFormat from joda-time. BTW, the 0000 zone offset is for UTC, so I could have omitted withZoneUTC(), but I still used it for the first date just to be safe:

  val oldDateString = "2021-02-28 13:38:00.597 0000"
  val OldFormat     = "yyyy-MM-dd HH:mm:ss.SSSZ"
  val NewFormat     = "EEE, MMM dd, yyyy HH:mm:ss z"

  val formatterOld = DateTimeFormat.forPattern(OldFormat)
  val formatterNew = DateTimeFormat.forPattern(NewFormat)

  val dt              = formatterOld.withZoneUTC().parseDateTime(oldDateString)
  val dateStringInUTC = formatterNew.withZoneUTC().print(dt)

  println(dt)              // 2021-02-28T13:38:00.597Z
  println(dateStringInUTC) // Sun, Feb 28, 2021 13:38:00 UTC

UPDATE: For Java 8 and newer, the java.time API is your friend. Similarly, withZoneSameInstant(ZoneOffset.UTC) was not really needed:

  val oldDateString = "2021-02-28 13:38:00.597 0000"
  val OldFormat     = "yyyy-MM-dd HH:mm:ss.SSSZZZ"
  val NewFormat     = "EEE, MMM dd, yyyy HH:mm:ss z"

  val formatterOld = DateTimeFormatter.ofPattern(OldFormat)
  val formatterNew = DateTimeFormatter.ofPattern(NewFormat)

  val zdt             = ZonedDateTime.parse(oldDateString, formatterOld)
  val dateStringInUTC = zdt.withZoneSameInstant(ZoneId.of("UTC")).format(formatterNew)

  println(zdt)             // 2021-02-28T13:38:00.597Z
  println(dateStringInUTC) // Sun, Feb 28, 2021 13:38:00 UTC

UPDATE: Switched to using ZoneId.of("UTC") instead of ZoneOffset.UTC because the latter does not get the String UTC printed at the end, even though ZoneOffset extends ZoneId, as @deHaar mentioned.

CodePudding user response：

If you could use java.time, you would need

a DateTimeFormatter for parsing Strings with the format of your input example, which is quite near to ISO standard, but is missing the 'T' between date and time of day
another DateTimeFormatter for outputting the temporal content in the desired format, which includes (English) abbreviations for day of week and month of year
an OffsetDateTime for parsing the String with the first DateTimeFormatter and
a ZonedDateTime for the temporal value in UTC

This is how I would do it in Java:

public static void main(String[] args) {
    // example String
    String utcDatetimeString = "2021-02-28 13:38:00.597 0000";
    // prepare a formatter that can parse a String of this format
    DateTimeFormatter dtfIn = DateTimeFormatter.ofPattern(
                                        "uuuu-MM-dd HH:mm:ss.SSSxxxx",
                                        Locale.ENGLISH
                                    );
    // parse it to an OffsetDateTime
    OffsetDateTime odt = OffsetDateTime.parse(utcDatetimeString, dtfIn);
    // then convert it to a ZonedDateTime applying UTC zone
    ZonedDateTime zdt = odt.atZoneSameInstant(ZoneId.of("UTC"));
    // prepare a formatter that produces the desired output
    DateTimeFormatter dtfOut = DateTimeFormatter.ofPattern(
                                        "EEE, MMM dd, uuuu HH:mm:ss zzz",
                                        Locale.ENGLISH
                                    );
    // and print the ZonedDateTime using the formatter
    System.out.println(zdt.format(dtfOut));
}

Output:

Sun, Feb 28, 2021 13:38:00 UTC