[jira] [Commented] (LANG-796) DateUtils.addDays does not work properly with daylight saving time (DST)

["Josh Chaitin-Pollak (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LANG-796?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14179981#comment-14179981 ] 

Josh Chaitin-Pollak commented on LANG-796:
------------------------------------------

I am affected by this situation as well, and I agree with [~nicola.barbiero] - As he quoted the Oracle specification at the top of bug: "Nearly all modern operating systems assume that 1 day = 24 × 60 × 60 = 86400 seconds in all cases".

Adding a day should add a 86400 seconds, in all cases, regardless of timezone.

> DateUtils.addDays does not work properly with daylight saving time (DST)
> ------------------------------------------------------------------------
>
>                 Key: LANG-796
>                 URL: https://issues.apache.org/jira/browse/LANG-796
>             Project: Commons Lang
>          Issue Type: Bug
>          Components: lang.time.*
>    Affects Versions: 3.3.2
>            Reporter: Nicola Barbiero
>             Fix For: Discussion
>
>
> {{DateUtils.addDays}} does not work properly with daylight saving time. The signature of the method is {{Date addDays(Date date, int amount)}} and the javadocs says:
> bq. Adds a number of days to a date returning a new object. The original date object is unchanged
> so if X=date.getTime() is the number of milliseconds of the date in input,
> the expected behaviour is that the returned Date has a number of milliseconds equal to X+amount*(86400000), where 86400000 is the number of milliseconds in one day.
> But when the calculation goes across the DST change date, the number of milliseconds added does not correspond to whole days.
> For example, here in Brussels, this code fragment:
> {code:java}
> Date input = DateUtils.parseDateStrictly("25-03-2012_00:00", new String[] { "dd-MM-yyyy_HH:mm" });
> Date output = DateUtils.addDays(input, 1);
> {code}
> will give:
> 'input' equals to "Sun Mar 25 00:00:00 CET 2012"    ==> input.getTime() equals to 1332630000000
> 'output' equals to "Mon Mar 26 00:00:00 CEST 2012"  ==> output.getTime() equals to 1332712800000
> where 1332712800000-1332630000000=82800000 < 86400000
> (in fact 82800000 is equivalent to 23h).
> Since {{addDays}} is working with objects Date, it should not be influenced by events like the DST.
> Proposed solution: replace the current implementation
> {code:java}
> public static Date add(Date date, int calendarField, int amount) {
>         if (date == null) {
>             throw new IllegalArgumentException("The date must not be null");
>         }
>         Calendar c = Calendar.getInstance();
>         c.setTime(date);
>         c.add(calendarField, amount);
>         return c.getTime();
>     }
> {code}
> based on Calendar with an implementation that works only with Date objects, for example:
> {code:java}
> public static Date add(Date date, int calendarField, int amount) {
>         if (date == null) {
>             throw new IllegalArgumentException("The date must not be null");
>         }
>         return new Date(input.getTime() + amount * 86400000l);
>     }
> {code}



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