CODEWITHSUNDEEP
javadatedatetime
idipous
idipous

Reputation: 2910

Date getTime() from Calendar in specific timezone

I have this code below:

Date now = CalendarUtils.getCalendar(getDefaultTimeZone())
                .getTime();

The CalendarUtils class has the below methods 

public static Calendar getCalendar(final TimeZone tz) {
    return getCalendar(CalendarUtils.getDate(), tz);
}

public static Calendar getCalendar(final Date time, final TimeZone tz) {
    final GregorianCalendar calendar = new GregorianCalendar();
    calendar.setTimeZone(tz);
    calendar.setTime(time);
    return calendar;
}

public static Date getDate() {
    return CalendarUtils.getDate(System.currentTimeMillis());
}

Where the getDefaultTimeZone() returns a timezone object in a specific timezone. Let's say Europe/Madrid.

However my application is running on a server in Rome.

The problem is that the code above is used to get the local time of Madrid. So at 12:30 am in Rome on Aug. 8th it is still 11:30 pm Aug. 7th in Madrid.

When I use

Date startOfDay = DateUtils.truncate(now, Calendar.DATE);

I would expect Aug. 7th 00:00:00 instead I get Aug 8th 00:00:00

I have read how Date returns the Millis from the Epoch but I would expect that it would return the millis from the Epoch of the date I ask from the Calendar.

When I use the query below at 12:30 am Aug 8th Rome time utilizing the two dates (now and startOfDay) I get results for the 8th of Aug instead the 7th (which is the local time in Madrid).

 public BigInteger getSumForDates(Date fromDate, Date toDate) {

    Session session = sessionFactory.openSession();
    BigInteger sum;
    try{
        sum = (BigInteger)session
            .createSQLQuery(
                    "SELECT SUM(column) FROM table 
                     WHERE (column2 at time zone vas_tz()) >=:fromDate 
                   AND (column2 at time zone vas_tz()) < :toDate")
                  .setTimestamp("fromDate", fromDate)
                  .setTimestamp("toDate", toDate).uniqueResult();
    }catch (final HibernateException e){
        LOGGER.error(e.getMessage());
        throw new ProjectRuntimeException();
    }finally{
        session.close();

    }

EDIT

The DateUtils is the one from package org.apache.commons.lang.time;

public static Date truncate(Date date, int field) {
    if (date == null) {
        throw new IllegalArgumentException("The date must not be null");
    }
    Calendar gval = Calendar.getInstance();
    gval.setTime(date);
    modify(gval, field, MODIFY_TRUNCATE);
    return gval.getTime();
}

When I say to return the millis for the date I have asked the Calendar for, I meant that if the calendar has supplied Aug 7th 11:30 pm (since I provided a timezone) then I would expect the millis from the Epoch until Aug 7th 11:30 adjusted for that timezone. Is this an incorrect expectation?

Upvotes: 0

Views: 434

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1499790

I have read how Date returns the Millis from the Epoch but I would expect that it would return the millis from the Epoch of the date I ask from the Calendar.

Then your expectation is incorrect - or you're not expressing your expectation clearly. There's only one Unix epoch: it's midnight UTC. A Date has no concept of a time zone - it's just the number of milliseconds since the Unix epoch.

It's not clear what your DateUtils class is, but anything which claims to truncate a Date to a day without specifying a time zone is somewhat dubious.

I would strongly advise you to use Joda Time or the Java 8 java.time classes - they're much simpler to work with than java.util.*. If you must use java.util.Date and java.util.Calendar, you'll need to work out which time zone you're interested, and specify that appropriately - using Calendar, not Date - when performing operations such as "truncate to day".

Upvotes: 2

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