Converting date from UTC to EST in Java?

Question

I\'m trying to convert a long timestamp that is UTC to Eastern Standard Time and am totally lost. Any hints would be great!

Time format should be : 11/4/03 8:14 PM

Answer 1

You should not think in terms of converting a Date to a different timezone. Dates in Java are, and should always be, in UTC.

Rather, you can set a particular timezone when you want to format a Date. Here is an example:

public static void main(String[] args) throws Exception {

    String tzid = "EST";
    TimeZone tz = TimeZone.getTimeZone(tzid);

    long utc = System.currentTimeMillis();  // supply your timestamp here
    Date d = new Date(utc);

    // timezone symbol (z) included in the format pattern for debug
    DateFormat format = new SimpleDateFormat("yy/M/dd hh:mm a z");

    // format date in default timezone
    System.err.println(format.format(d));

    // format date in target timezone
    format.setTimeZone(tz);
    System.err.println(format.format(d));

}

Output for me (my default timezone is GMT):

11/12/19 10:06 AM GMT
11/12/19 05:06 AM EST

Alternatively, you can set the timezone on a Calendar, and then access the Calendar fields you require. For example:

    Calendar c = Calendar.getInstance(TimeZone.getTimeZone("EST"));
    c.setTimeInMillis(utc);
    System.err.printf("%d/%d/%d %d:%d %s\n", c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH), c.get(Calendar.HOUR), c.get(Calendar.MINUTE), (c.get(Calendar.AM_PM) == Calendar.AM ? "AM" : "PM"));

(This does not give you the exact pattern you requested.)