Get formatted string from Calendar

Question

I've got a Calendar Date in Java.

I need to convert it in a String with this format :

2020-12-29T00:00:00+01:00

How can I do it?

Thank you so much for your help.

Answer 1

Get the Date object by calling Calendar#getTime and format it using a SimpleDateFormat with the format, yyyy-MM-dd'T'HH:mm:ssXXX.

Note: Since the desired string has timezone offset of +01:00 hours, make sure you set the timezone of the SimpleDateFormat object to TimeZone.getTimeZone("GMT+1") before calling SimpleDateFormat#format.

Demo:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

public class Main {
    public static void main(String[] args) throws ParseException {
        Calendar calendar = Calendar.getInstance();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssXXX");
        sdf.setTimeZone(TimeZone.getTimeZone("GMT+1"));
        Date date = calendar.getTime();
        String formatted = sdf.format(date);
        System.out.println(formatted);
    }
}

Another example:

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

public class Main {
    public static void main(String[] args) throws ParseException {
        String dateTimeString = "2020-12-29T00:00:00+01:00";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssXXX");
        Date obj = sdf.parse(dateTimeString);
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(obj);

        // Formatting this calendar object
        Date date = calendar.getTime();
        sdf.setTimeZone(TimeZone.getTimeZone("GMT+1"));
        String formatted = sdf.format(date);
        System.out.println(formatted);
    }
}

Output:

2020-12-29T00:00:00+01:00

Answer 2

java.time

I recommend that you use java.time, the modern Java date and time API, for your date and time work.

Here’s a formatter for your desired format:

private static final DateTimeFormatter formatter
        = DateTimeFormatter.ofPattern("uuuu-MM-dd'T'HH:mm:ssXXX");

With this we may do:

    ZoneId zone = ZoneId.of("Asia/Barnaul");
    ZonedDateTime dateTime
            = LocalDate.of(2020, Month.DECEMBER, 29).atStartOfDay(zone);
    String formatted = dateTime.format(formatter);
    System.out.println(formatted);

Output from this example snipoet is:

2020-12-29T00:00:00+07:00

If you cannot avoid getting a Calendar

If you are getting a Calendar object from a legacy API that you cannot afford to upgrade to java.time just now, convert it to ZonedDateTime. It is almost certainly really a GregorianCalendar (or formatting into that format would not make much sense), which makes the conversion straightforward.

    Calendar yourCalendar = getCalendarFromLegacyApi();
    ZonedDateTime dateTime
            = ((GregorianCalendar) yourCalendar).toZonedDateTime();

The rest is as before, as is the output.

If you need to take into account the possibility that the Calendar is not a GregorianCalendar, use this slightly more complicated conversion instead:

    ZonedDateTime dateTime = yourCalendar.toInstant()
            .atZone(yourCalendar.getTimeZone().toZoneId());

Link

Oracle tutorial: Date Time explaining how to use java.time.