CODEWITHSUNDEEP
javadatetimestamp
user1156596
user1156596

Reputation: 601

Converting timestamp to hours in java

I have the following timestamp stored in a long variable: 1471906800000 this stores the date 18/01/2017 00:00:00

I'm trying to create another timestamp that will contain the same date as stored in the first timestamp, but with the time being 23:59:59 -

I don't even know where to start

How could I achieve this in the most simple way possible in Java?

Thanks.

Upvotes: 0

Views: 3296

Answers (3)

Andy Turner
Andy Turner

Reputation: 140328

I'm assuming that you don't specifically want the time at 23:59:59, but rather a time 1 minute before the start of the next day.

You should use a date/time library. I know jodatime better, so this example is written using that, but you may be able to use the Java 8 time API instead.

DateTime today = new DateTime(1471906800000L, TIME_ZONE);
// You may want to check that today is actually at the start of the day.
// e.g. today.equals(today.withTimeAtStartOfDay());

DateTime lastMinuteOfToday =
     today.toLocalDate()
         .plusDays(1)
         .toDateTimeAtStartOfDay(TIME_ZONE)
         .minusMinutes(1);

long lastMinuteOfTodayMillis = lastMinuteOfToday.getMillis();

Knowing the timezone is important to do this correctly.

Upvotes: 1

Basil Bourque
Basil Bourque

Reputation: 338614

Both of the other Answers use outmoded classes, now supplanted by the java.time classes.

Perhaps your input number is a count of milliseconds from the epoch of first moment of 1970 in UTC (1970-01-01T00:00:00Z). But I do not get the result you stated in the question.

long input = 1_471_906_800_000L ;
Instant instant = Instant.ofEpochMilli( input );

input: 1471906800000

instant: 2016-08-22T23:00:00Z

But you expected the value of 18/01/2017 00:00:00, off by a few months. If your input is not a count of milliseconds from 1970-01-01T00:00:00Z, you need to edit your Question to specify.

If you made a mistake in your expected output, then let's proceed to set the time-of-day.

If you wanted the second before the end of the day, I suggest subtracting a second from the start of the following day rather than hard-coding the time of 23:59:59. That time-of-day may be invalid because of anomalies such as Daylight Saving Time (DST). Also, unless you meant intend to work in UTC, you need to move into the desired/expected time zone.

ZoneId z = ZoneId.of( "America/Montreal" );
ZonedDateTime zdt = instant.atZone( z );

Extract a LocalDate, for a date-only value without time-of-day and without time zone.

LocalDate ld = zdt.toLocalDate();

Move to next day.

LocalDate ldNextDay = ld.plusDays( 1 );

Ask for first moment.

ZonedDateTime zdtNextDay = ldNextDay.atStartOfDay( z );

Subtract a second to move back into previous day.

ZonedDateTime zdtPreviousDay = zdtNextDay.minusSeconds( 1L );

However, I suspect you are taking the wrong approach to handling date-time values. Rather than trying to determine the end of a day, I strongly suggest you follow the common practice of using the Half-Open approach to spans of time. In Half-Open, the beginning is inclusive while the ending is exclusive.

So a full day starts with the first moment of one day and runs up to, but not including, the first moment of the next day. This way you avoid the problem of the last second or trying to get the infinitely divisible fraction of a second. 

ZonedDateTime zdtDayStart = LocalDate.of( 2017 , Month.JANUARY , 18 ).atStartOfDay( 1 );
ZonedDateTime zdtDayStop = zdtDayStart.plusDays( 1 );

You may find the Interval class in the ThreeTen-Extra project helpful.

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

Where to obtain the java.time classes?

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

Upvotes: 1

Jens
Jens

Reputation: 69440

Using Calendar will help you:

  long l = 1471906800000l;
  Date date = new Date(l);
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(date);
  calendar.set(Calendar.HOUR, 23);
  calendar.set(Calendar.MINUTE, 59);
  calendar.set(Calendar.SECOND, 59);
  l = calendar.calendar.getTimeInMillis();

Upvotes: 1

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