public static Timestamp getCurrentTimeGMT() {

        Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
        long time = c.getTimeInMillis();
        long offset = TimeZone.getDefault().getOffset(time);
        return new Timestamp(time - offset);

    }

public static Timestamp getCurrentTimeGMT3() {

    Calendar c = Calendar.getInstance(TimeZone.getTimeZone("GMT+3"));
    long time = c.getTimeInMillis();
    long offset = TimeZone.getDefault().getOffset(time);
    return new Timestamp(time - offset);

}

int h = c.get(Calendar.HOUR_OF_DAY);
int m = c.get(Calendar.MINUTE);
int s = c.get(Calendar.SECOND);

TimeZone default = TimeZone.getDefault();

TimeZone.setDefault(TimeZone.getTimeZone("GMT+3"));
Calendar cal = Calendar.getInstance();
cal.setTime(new Date(System.currentTimeMillis()));
Date date = cal.getTime(); // converted date time
System.out.println(date.toString());

// Set Back to System Default
TimeZone.setDefault(default);

public class GetZoneDateTime {

public static void main(String[] args) throws Exception {
    String reqTzId = "Asia/Singapore";

    LocalDateTime now = LocalDateTime.now();
    System.out.println("Local Now: " + now + " TimeZone: " + TimeZone.getDefault());

    ZoneId zoneId = ZoneId.of(reqTzId);
    System.out.println("Req TimeZone : " + zoneId);

    LocalDateTime localNow = LocalDateTime.now(zoneId);
    System.out.println("tzLocalDateTime: " + localNow);

    ZonedDateTime zoneNow = ZonedDateTime.now(zoneId);
    System.out.println("tzZonedDateTime: " + zoneNow);
}