Determine if a date is during DST

Is there an easy way in coldfusion to determine if a give date/time
happened/will happen during Daylight Saving Time? I can find out if the server
is currently observing DST. But I need to know this for a time stamp that was
recorded without time zone info. I know that the time zone this was recorded
for does observer DST, but I don't want to have to write a function to parse
out if the day falls between April and October.

Any help? Or am I going to have to do this the hard way?

[PaulH]

[url]http://www.sustainablegis.com/projects/tz/testTZCFC.cfm[/url] should do the trick.

Ok, that is along the same line as what I am needing, but not quite. What I
need is to determine if a date happend during daylight saving time. But that
information is not stored in the data. Basicly what I need is an algorithm for
calculating if a date falls between the begining and ending of DST. I tried
using dateConvert(local2utc, date) as I know that the dates were recorded with
DST taken into account. But that is giving the same UTC offset for every day
of the year. (the server is in DST right now).

[Another Phil]

Look in the Java API for Timezones at java.sun.com. There is a method that
allows you to check and see if a date / time falls in daylight savings.

An example of how to use that in Cold Fusion is the following:

<cfobject type="java" class="java.util.TimeZone" name="TZ" action="create">
<cfset tzdate = tzdatechk.init(#DateFormat(thedate, 'yyyy')#,
#DateFormat(thedate, 'mm')#, #DateFormat(thedate, 'dd')#)>
<cfif #ret.inDaylightTime(tzdate)# EQ true>
**do stuff**
</cfif>

Hope this helps.

Phil

Very cool, Phil, thanks!
I'm not that familiar with using java objects in coldfusion code. But, I can
see how they would be very powerful. (Personaly I'd rather by writting code in
java than cfml anyway)

[PaulH]

if you looked at that CFC you should have seen a method isDST() to handle that.
you pass it a valid cf datetime & a timezone ID & it would return whether or
not that datetime is in DST or not. not all tz have DST (there are islands of
non-DST tz in the US for example), not all tz start/end DST aty the same time.