Re: NSTimestamp problem
Re: NSTimestamp problem
- Subject: Re: NSTimestamp problem
- From: Chuck Hill <email@hidden>
- Date: Mon, 18 Dec 2006 19:05:04 -0800
On Dec 18, 2006, at 6:45 PM, Jerry W. Walker wrote:
Hi, Dan,
You're dealing with a Daylight Savings Time problem.
Yes, the notorious One Hour Shift.
I haven't tried to keep up with Java's calendar routines over the
last few months, but if you go to the page on the US Naval
Observatory web site that describes clock changes at:
http://aa.usno.navy.mil/faq/docs/daylight_time.html
...the first paragraph says:
Currently, daylight time begins in the United States
on the first Sunday in April and ends on the last
Sunday in October. On the first Sunday in April,
clocks are set ahead one hour at 2:00 a.m. local
standard time, which becomes 3:00 a.m. local
daylight time. On the last Sunday in October, clocks
are set back one hour at 2:00 a.m. local daylight
time, which becomes 1:00 a.m. local standard time.
These dates were recently modified with the
passage of the Energy Policy Act of 2005, Pub. L.
no. 109-58, 119 Stat 594 (2005). Starting in
March 2007, daylight time in the United States
will begin on the second Sunday in March and end
on the first Sunday in November.
...and therein lies your problem.
As for a workaround, I'm not sure what to suggest. However, I
thought that the later JVMs had adapted to the change in law.
I think that is exactly the problem. We are not in DST now, but late
March will be. Java is very "accurate" WRT time and does not handle
it as we would in day to day life. 9AM March 21 is not exactly N x
24 hours away, it is N x 24 +/- 1 depending on which way you are
crossing the DST boundary. If you have dates at midnight, even the
date will change! Much fin ensues. If you don't need the time,
setting it to noon will avoid the date shift. That is of no use to
you. You can use different formatters (with the time zone set
differently) for dates in and out of DST. You could also store the
date (at noon) in one field and the in another.
Java. Dates. If there is a hell on earth for developers, it is this.
Chuck
On Dec 18, 2006, at 8:31 PM, Dan Faber wrote:
Hi everyone:
I have just run into an apparent NSTimestamp problem. I have a
scheduling program, and it has been working well. Recently we
tried to schedule an appt for March, and the NSTimestamp is giving
us back a time that is one hour earlier than the time that is
designated. This occurs between March 11 and March 31, 2007, a 3
week period. The problem does not seem to occur for dates before
that period or afterwards. It does not appear to be an
NSTimestampFormatter problem, as it exists with or without using
the formatter.
The time is correct in the database after a save, but it
immediately gets displayed an hour early. The problem occurs with
two different versions of the mysql-connector (including the most
recent). It occurs on two different machines, both running OSX
version 10.4.8.
Converting the date to java.util.GregorianCalendar appears to
produce the correct result for
java.util.GregorianCalendar.HOUR_OF_DAY.
So far I have not seen anything on the list about this. Anyone
have any ideas what's up?
Dan Faber
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