CST to UTC conversion in java

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

public class CalendarFormat {
    public static final String STARTTIME = " 00:00:00";
    public static final String ENDTIME = " 23:59:59";
    public static final String TIME_ZONE_UTC = "UTC";
    public static final String INPUT_DATE_FORMAT = "yyyyMMdd HH:mm:ss";
    public static final String ISO_8601_FORMAT_MILLISECOND = "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'";


public static void main(String[] args) {
    CalendarFormat.getDateFormat("20210825_20210826", "CST");
}

    public static String mySqlDateFormatInUtc(String date, String time, String inputTimezoneId) {
        final TimeZone utcTimeZone = TimeZone.getTimeZone(CalendarFormat.TIME_ZONE_UTC);
        SimpleDateFormat input = new SimpleDateFormat(INPUT_DATE_FORMAT);
        input.setTimeZone(TimeZone.getTimeZone(inputTimezoneId));
        String dateToBeformatted = date + " " + time;
        SimpleDateFormat output = new SimpleDateFormat(CalendarFormat.ISO_8601_FORMAT_MILLISECOND);
        output.setTimeZone(utcTimeZone);
        String format = null;
        try {
            format = output.format(input.parse(dateToBeformatted));
            System.out.println(format);
        } catch (ParseException e) {
            e.printStackTrace();
        }
        return format;
    }
    
    public static String[] getDateFormat(String dateRangeString, String inputTimezoneId) {
        String[] dates = dateRangeString.split("_");
        String from = CalendarFormat.mySqlDateFormatInUtc(dates[0], CalendarFormat.STARTTIME, inputTimezoneId.trim());
        String to = CalendarFormat.mySqlDateFormatInUtc(dates[1], CalendarFormat.ENDTIME, inputTimezoneId.trim());
        dates[0] = from;
        dates[1] = to;
        return dates;
    }
}

This is my class.. here i am changing the time zone CST to UTC so its adding +5 hrs because of its adding 5hrs its changing the date 25-26 to 25-27 .. but i want the output same as 25-26 same even after the time zone conversion… please anyone help me out struck on this issue for 2 days…

for the above code .. output was like this

2021-08-25 T 05:00:00.000Z 2021-08-27 T 04:59:59.000Z

but i want the output as

2021-08-25 T 00:00:00.000Z 2021-08-26 T 23:59:59.000Z

Answer

Your own default time zone is not relevant

You want 20210825 converted to 2021-08-25T05:00:00.000Z. the start of the day in UTC. That’s easy when you know how. Just don’t mix in Central Time or any other time zone. They are not relevant.

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

private static final DateTimeFormatter ISO_8601_FORMAT_MILLISECOND
        = new DateTimeFormatterBuilder().append(DateTimeFormatter.ISO_LOCAL_DATE)
                .appendLiteral('T')
                .appendPattern("HH:mm.ss.SSS")
                .appendOffsetId()
                .toFormatter(Locale.ROOT);

public static String[] getDateFormat(String dateRangeString) {
    String[] dates = dateRangeString.split("_");
    String from = mySqlDateFormatInUtc(
            LocalDate.parse(dates[0], DateTimeFormatter.BASIC_ISO_DATE),
            LocalTime.MIN);
    String to = mySqlDateFormatInUtc(
            LocalDate.parse(dates[1], DateTimeFormatter.BASIC_ISO_DATE),
            LocalTime.MAX);
    dates[0] = from;
    dates[1] = to;
    return dates;
}

public static String mySqlDateFormatInUtc(LocalDate date, LocalTime time) {
    return date.atTime(time).atOffset(ZoneOffset.UTC).format(ISO_8601_FORMAT_MILLISECOND);
}

Let’s try it out:

    String[] result = CalendarFormat.getDateFormat("20210825_20210826");
    System.out.println(Arrays.toString(result));

Output is:

[2021-08-25T00:00.00.000Z, 2021-08-26T23:59.59.999Z]

We can do even better, though:

1. Don’t format strings for transferring date and time to your database. Transfer proper date-time objects. I don’t know your SQL database nor your database driver, but this probably means transferring the OffsetDateTime that we got from date.atTime(time).atOffset(ZoneOffset.UTC). For example:

       yourPreparedStatement.setObject(1, yourOffsetDateTime);
   

2. If for some reason you insist on formatting into strings, you probably don’t need the formatter. OffsetDateTime.toString() produces ISO 8601 format. When the milliseconds are 0, they will be left out in accordance with the ISO 8601 standard, so that should still work.

3. Do not represent the end of the day by 23:59:59. One, it’s wrong, the day does not end until the next day begins 1 second later. Two, you risk having times falling in the gap you have artificially created between the dates, causing mysterious errors in your application. Represent the end of the day by 00:00:00 on the next day and always treat is as exclusive: a date and time belongs to your interval if it is on or after the start and strictly before the end. This will ensure correct limits.

Link

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