CODEWITHSUNDEEP
javadatejava-7
Shakka
Shakka

Reputation: 137

Converting a UTC Date into a Date of different timezone

I receive a date that represents a datetime in utc. Lets say: 21-Jun-2019 10:00

I'd like to convert this datetime to the timezone "Europe/Vienna" expecting: 21-Jun-2019 12:00

I do not understand, why my code below shows the same time for both

        Date utcFinish = new Date(new Date().getYear(), Calendar.JUNE, 21);
        TimeZone europeVienna = TimeZone.getTimeZone("Europe/Vienna");
        Calendar finishInViennaTime = Calendar.getInstance(europeVienna);
        finishInViennaTime.setTime(utcFinish);

        System.out.println(format.format(utcFinish));
        System.out.println(format.format(finishInViennaTime.getTime()));

Output:

2019-06-21 00:00
2019-06-21 00:00

What would be the best java7 only (no joda, localdate pls) solution!? Thank you

EDIT: I also tried:

        SimpleDateFormat formatWithTimezone = new SimpleDateFormat("yyyy-MM-dd HH:mm");
        formatWithTimezone.setTimeZone(TimeZone.getTimeZone("Europe/Vienna"));

        SimpleDateFormat formatonly = new SimpleDateFormat("yyyy-MM-dd HH:mm");

        Date utcDate = new Date(new Date().getYear(), Calendar.JUNE, 21);

        System.out.println(formatonly.format(utcDate));
        System.out.println(formatWithTimezone.format(utcDate));

Output:

2019-06-21 00:00
2019-06-21 00:00

SOLUTION

Thanks for all the solutions. In the end the problem was the default timezone. Here is my current solution (further feedback welcome!):

        // Unfortunately this date has the wrong time zone (Local Time Zone),
        // because Date assumes Local Time Zone the database stores timestamps 
        // in utc that's why I now convert to a datestring and reparse

        Date finishTimeWrongTimeZone = new Date(new Date().getYear(), Calendar.JUNE, 21);
        // in reality i call the db here like getFinishTime();

        // get the plain date string without time shifting
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MMM-dd HH:mm");
        String dateWithoutTimeZone = formatter.format(finishTimeWrongTimeZone);

        // add the timezone to the formatter and reinterpret the datestring
        // effectively adding the correct time zone the date should be in
        formatter.setTimeZone(TimeZone.getTimeZone("UTC"));

        String finishTime = null;
        try {

            Date dateWithCorrectTimeZone = formatter.parse(dateWithoutTimeZone);

            // Convert to expected local time zone (europe/vienna)
            formatter.setTimeZone(TimeZone.getTimeZone("Europe/Vienna"));
            finishTime = formatter.format(dateWithCorrectTimeZone);

        } catch (Exception e) {
            e.printStackTrace();
        }
        System.out.println(finishTime);

Upvotes: 0

Views: 1145

Answers (4)

TiiJ7
TiiJ7

Reputation: 3402

Modern (java.time) solution

I have a version for the old API below like you asked, but for completeness, I will also provide the more modern solution. I recommend you to look into ThreeTen-Backport if updating Java is not an option:

ZonedDateTime zdt = LocalDateTime.of(
    Year.now().getValue(), Month.JUNE, 21, 10, 0, 0
).atZone(ZoneOffset.UTC);

System.out.println(
    zdt.withZoneSameInstant(ZoneId.of("Europe/Vienna"))
      .format(DateTimeFormatter.ofPattern("uuuu-MM-dd HH:mm"))
);

Old (java.util) solution

new Date(...) is deprecated, and you should not use it. If you really need to stick to the old API; you'll need to use Calendar:

Calendar utcFinish = new GregorianCalendar(TimeZone.getTimeZone("UTC"));
utcFinish.set(Calendar.MONTH, Calendar.JUNE);
utcFinish.set(Calendar.DATE, 21);
utcFinish.set(Calendar.HOUR_OF_DAY, 10);
utcFinish.set(Calendar.MINUTE, 0);

And then use a DateFormat with the time zone that you actually wish to print it with:

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm");
TimeZone europeVienna = TimeZone.getTimeZone("Europe/Vienna");
format.setTimeZone(europeVienna);

System.out.println(format.format(utcFinish.getTime()));

Output

Both solutions should output (at time of writing, in 2019):

2019-06-21 12:00

Upvotes: 1

Joakim Danielson
Joakim Danielson

Reputation: 51892

I use one formatter object and changes the time zone on it

SimpleDateFormat format = new SimpleDateFormat("dd-MM-yyyy HH:mm"); format.setTimeZone(TimeZone.getTimeZone("UTC"));

Date dUtc = format.parse("21-06-2019 10:00");
System.out.println(dUtc);

TimeZone europeVienna = TimeZone.getTimeZone("europe/vienna");

format.setTimeZone(europeVienna);
String sVienna = format.format(dUtc);
System.out.println(sVienna);

Upvotes: 1

spi
spi

Reputation: 1735

Alter the Timezone before doing the format. The date will be "converted" accordingly, but as we already told you, this old coding style has a lot of flaws:

public static void main(String[] x) {
    Date instant = new Date(new Date().getYear(), Calendar.JUNE, 21); // this call assumes the Timezone is your current default (system dependant).
    DateFormat sdf = SimpleDateFormat.getDateTimeInstance();

    sdf.setTimeZone(TimeZone.getTimeZone("Europe/Vienna"));
    System.out.println(sdf.format(instant)); //21 juin 2019 00:00:00

    sdf.setTimeZone(TimeZone.getTimeZone("Europe/Greenwich"));
    System.out.println(sdf.format(instant)); // 20 juin 2019 22:00:00

}

Upvotes: 1

Viren
Viren

Reputation: 1

Please use SimpleDateFormat to convert timezone

SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm");
Date utcFinish = new Date(new Date().getYear(), Calendar.JUNE, 21);
TimeZone europeVienna = TimeZone.getTimeZone("Europe/Vienna");
format.setTimeZone(europeVienna);
System.out.println(format.format(utcFinish));

Upvotes: 0

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