在Java中生成两个日期之间的日开始时间和日结束时间。 夏时制问题

Question

I have to generate days between two two dates. for ex:

1420090495000 -> Jan 1, 2015

1430458495000 -> May 1, 2015

I have to generate timestamps for all days like

Jan 1, 2015 00:00:00 - Jan 1, 2015 23:59:59

Jan 2, 2015 00:00:00 - Jan 2, 2015 23:59:59

Jan 3, 2015 00:00:00 - Jan 3, 2015 23:59:59

so on

I am able to do that. But I am getting some problem with day light saving issue. On march somewhere it is generating like this

Mar 8, 2015 00:00:00 - Mar 9, 2015 00:01:00 Which is wrong and it should be like Mar 8, 2015 00:00:00 - Mar 8, 2015 23:59:59

I found it because of day light saving issue. How to solve this issue ?

My code is:

public static List<String> getDatesRange(long start, long end, String tzOffset) {
//tzOffset is 420. for USA

        TimeZone tz = TimeZone.getTimeZone(tzOffset);

        List<String> dates=new ArrayList();
        Calendar calendar = Calendar.getInstance(tz);

        calendar.set(Calendar.DAY_OF_WEEK, 1);
        calendar.set(Calendar.HOUR, 0);
        calendar.set(Calendar.MINUTE, 0);
        calendar.set(Calendar.SECOND, 0);
        calendar.set(Calendar.MILLISECOND, 0);


        while (start<end) {
            calendar.setTimeInMillis(start);
            long startTime = calendar.getTimeInMillis();
            int year= calendar.getWeekYear();


            long endTime = start + (1 * 24 * 3600 * 1000L);

            if(endTime<end) {
                endTime-=1000;
                System.out.println("Start Date= " + new Date(new Timestamp(start).getTime())+" ("+startTime+"), End Date= "+new Date(new Timestamp(endTime).getTime())+"("+endTime+")");

dates.add(startTime+"-"+endTime);
                start= endTime+1000;
            }
            else{
                System.out.println("Start Date= " + new Date(new Timestamp(start).getTime()) + " (" + startTime + "), End Date= " + new Date(new Timestamp(end).getTime()) + "(" + end + ")");
                start=end;
                dates.add(startTime+"-"+end);
            }
        }
        return dates;
    }

Answer 1

The problem is that you want to print dates without the notion of time zones (although the start dates depends on the tzOffset argument). If you use Java 8, the new Java time API has a class specifically designed for that: LocalDate .

So your method can be done by first determining the start and end day based on the timestamp and the time zone then get rid of all time zone considerations. And to print the range you can "cheat" by hardcoding the start/end time in the formatter.

public static List<String> getDatesRange(long start, long end, String tzOffsetMinutes) {
  Instant startInstant = Instant.ofEpochMilli(start);
  Instant endInstant = Instant.ofEpochMilli(end);

  int offsetSeconds = Integer.parseInt(tzOffsetMinutes) * 60;
  ZoneOffset offset = ZoneOffset.ofTotalSeconds(offsetSeconds);
  LocalDate startDate = OffsetDateTime.ofInstant(startInstant, offset).toLocalDate();
  LocalDate endDate = OffsetDateTime.ofInstant(endInstant, offset).toLocalDate();

  List<String> dates = new ArrayList<> ();
  DateTimeFormatter fmt = DateTimeFormatter.ofPattern(
                                         "MMM d, yyyy 00:00:00 - MMM d, yyyy 23:59:59");

  for (LocalDate d = startDate; !d.isAfter(endDate); d = d.plusDays(1)) {
    dates.add(fmt.format(d));
  }
  return dates;
}

You can probably do something similar with Calendars.

Answer 2

There are a couple things I wonder about this:

• Why use Longs to define dates?
• Why return a list of Strings instead of a list of Dates?
• Why take the timezone into consideration at all in a case like this?

Nevertheless, you can achieve this simply using Calendar and SimpleDateFormat , like this:

public static Calendar getDayStart(final long timeInMillis) {
    final Calendar cal = Calendar.getInstance();
    // end time as a date
    cal.setTimeInMillis(timeInMillis);

    cal.set(Calendar.HOUR, 0);
    cal.set(Calendar.MINUTE, 0);
    cal.set(Calendar.SECOND, 0);
    cal.set(Calendar.MILLISECOND, 0);

    return cal;
}

public static List<String> getDatesRange(final long start, final long end) {

    final Calendar cal = getDayStart(start);
    final Date startDate = cal.getTime();

    final Calendar calEnd = getDayStart(end);
    //adding one day because of the strict comparison in the while below
    calEnd.add(Calendar.DAY_OF_YEAR, 1);
    final Date endDate = calEnd.getTime();

    final SimpleDateFormat formatter = new SimpleDateFormat("MMM d, yyyy HH:mm:ss");

    final List<String> dates = new ArrayList<String>();
    final Date dayEnd;
    String currentDay = "";

    while(cal.getTime().before(endDate)) {
        currentDay = formatter.format(cal.getTime());
        currentDay += " - ";
        //going to the end of the day
        cal.add(Calendar.DAY_OF_YEAR, 1);
        cal.add(Calendar.SECOND, -1);
        currentDay += formatter.format(cal.getTime());
        //going to next day again and continue the loop
        cal.add(Calendar.SECOND, 1);
        //add what we computed to the list of days
        dates.add(currentDay);
    }

    return dates;
}