Here is a (simple?) problem:

First I have a user that is in hypothetical time zone A. This time zone has a spring forward daylight savings change on March 11/2012 @ 02:00. This means that there are only 23 hours in that day where 02:00 does not exist.

Assume the application has 24 hourly values to display for that day:

March 11th 00:00 value 0
March 11th 01:00 value 1
March 11th 02:00 value 2
…
March 11th 21:00 value 21
March 11th 22:00 value 22
March 11th 23:00 value 23

Assume also that the data above is stored in the database as UTC and some magic is applied to convert the date so that a normal hour displays correctly (e.g. May 5th 15:00 UCT in the database shows up as May 5th 15:00 in the users browser/time zone).

The question is: How do you display all 24 hours in that user’s browser? If you haven’t taken this scenario into account, what likely happens is the 24 hours are displayed but the hour/value pairs get out of step at the time change and the last hour bleeds into the next day:

March 11th 00:00 value 0
March 11th 01:00 value 1
March 11th 03:00 value 2 (notice that at this point the value is out of step with the hour)
…
March 11th 22:00 value 21
March 11th 23:00 value 22
March 12th 00:00 value 23 (the 24th hour falls on the next day)

Has anyone encountered this issue and addressed it?

1. keep the dates with the correct UTC time and extend all the display components to be timezone aware. depending on your app this could be a ton of work.

2. store the dates incorrectly (ie ignore timezone completely) and store the timezone in a separate field (if you need it). This really only creates an issue when data goes to/from the server so that is the main problem you then need to solve.

I decided to go with #2 because, even if you re-write all the display classes, you still have no clue what timezone you are dealing with when the data goes to the server. You know the UTC time but you have no idea what timeZone people want to see.

I wrote an adapter class that all data goes through whenever it goes to/from the server. It looks for any dates and reverses the timezone offset that is on the client. In other words, 3pm in the local timezone gets converted to 3pm UTC. (we convert everything to UTC because that is the timezone of our server)

The server saves the 3PM, however it doesn’t save timezones so it just gets saves as plain old 3PM with timezone not specified. When if need the timezone we save it as text in a separate field.

When data comes back from the server of course it is 3PM UTC which is wrong, so you just re-apply the offset to bring it back to 3PM local time.

In other words, it is always saved as 3PM everywhere.

To figure out how to convert to/from UTC, create a dummy Date object and then use date.timezoneOffset to tell you how many hours to add/subtract.

This solution, of course, it is only useful when everybody wants to see the same thing on their client, ie everybody wants to see 3PM. If people want things converted into their own time then Flex already works as-is. (i think it’s stupid though!)