Re: [JDBC] JDBC Driver and timezones

From:

Lew <noone@lewscanon.com>

Newsgroups:

pgsql.interfaces.jdbc,comp.lang.java.programmer

Date:

Wed, 19 May 2010 11:33:30 -0400

Message-ID:

<ht10cb$vb2$1@news.albasani.net>

Kris Jurka

I think the problem is that the Java specification for java.sql.Time
requires that the date portion be filled in with 1970-01-01. So when
trying to determine the zone shift to apply when printing it out, it is
checking with that date instead of today's date as you are expecting.

When reading a timetz value in, we don't need to determine what the zone
shift is, it's explicit, so in this case we shift by the explicit DST
amount. When printing it back out, the original zone offset has been
discarded and we shift by the non-DST amount because the date 1970-01-01
doesn't use DST. I think we'd like to be able to override the
getTimezoneOffset value for the Time object, but there's no easy way to
do that without creating our own PgTime object.

On 05/19/2010 06:43 AM, John Lister wrote:

Hi, I spotted an issue regarding Daylight savings and timezones a while
ago that affected UK times so it may be possible that it does the same
in German ones. From memory - essentially the driver uses the epoch date
to work out DST which unfortunately coincides with a year (1970) when
the UK temporarily changed its DST rules.

This issue came up in pgsql.interfaces.jdbc and it seemed worth bringing into
the wider Java world since it's not Postgres-specific. The problem is that
java.sql.Time values are date-agnostic so might not reflect the intended DST
offset when referencing times relevant to "now".

This might be worth a bug report, or perhaps the problem is intractable and
requires the explicit workaround that the database folks find they must use.
Perhaps the new date/time libraries will address this somehow.

Opinions or assessments?

--
Lew