Get formatted string from Calendar

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.

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