R – Date and time handling in applications serving clients in multiple time-zones

datetimeinternationalizationlocalizationtimezoneutc

The internationalization problems associated with string handling can pretty much be solved by following the advice: use Unicode and store everything as UTF-8 in your database, then you'll be able to serve clients using all the world's languages.

But what about the internationalization problems associated with date/time handling?

Questions:

Are there similar easy-to-follow best practices for solving the internationalization issues surrounding time handling?
How do you make sure your applications can serve clients operating in different time zones? What issues did you encounter and how did you solve them?

Best Answer

I have following advices,

Store all your time in database with one timezone, preferably Zulu (GMT).
Assign a timezone to each user at registration. We normally figure this out from the language of the registration page or the code embedded in the promotion link. Sometimes, we have to ask user.
Make clients timezone-aware. This means client can't display time from server as is. Must be displayed in local timezone and in local format.
Client should make some effort to get timezone info of the system. If not, server can guess from various data. We got good results using language first, then IP address. In any case, client needs to display time with zone info so user knows what's going on when time is wrong.
Need special flags for certain time values that's not affected by timezone. We had a mistake that user's birthday changes when they change their locale. Other things belonging to this category including holidays, store hours etc.
If you have to sync up clock with server, please don't change system time, just store the delta in your client. We had a security requirement that the clock must be in sync with host. So our client syncs system clock with our server on startup. That's the wrong thing to do. For older systems like Windows 95 with no timezone, we changed their time into GMT. Finally the older clients went away but we are facing a new issue is that we messed up the accurate time from NTP.

Hope some of our mistakes will help you to avoid them.

Related Solutions

Java – How to get the current date and time in UTC or GMT in Java

java.util.Date has no specific time zone, although its value is most commonly thought of in relation to UTC. What makes you think it's in local time?

To be precise: the value within a java.util.Date is the number of milliseconds since the Unix epoch, which occurred at midnight January 1st 1970, UTC. The same epoch could also be described in other time zones, but the traditional description is in terms of UTC. As it's a number of milliseconds since a fixed epoch, the value within java.util.Date is the same around the world at any particular instant, regardless of local time zone.

I suspect the problem is that you're displaying it via an instance of Calendar which uses the local timezone, or possibly using Date.toString() which also uses the local timezone, or a SimpleDateFormat instance, which, by default, also uses local timezone.

If this isn't the problem, please post some sample code.

I would, however, recommend that you use Joda-Time anyway, which offers a much clearer API.

Php – How to get the current date and time in PHP

The time would go by your server time. An easy workaround for this is to manually set the timezone by using date_default_timezone_set before the date() or time() functions are called to.

I'm in Melbourne, Australia so I have something like this:

date_default_timezone_set('Australia/Melbourne');

Or another example is LA - US:

date_default_timezone_set('America/Los_Angeles');

You can also see what timezone the server is currently in via:

date_default_timezone_get();

So something like:

$timezone = date_default_timezone_get();
echo "The current server timezone is: " . $timezone;

So the short answer for your question would be:

// Change the line below to your timezone!
date_default_timezone_set('Australia/Melbourne');
$date = date('m/d/Y h:i:s a', time());

Then all the times would be to the timezone you just set :)

Best Answer

Related Solutions

Java – How to get the current date and time in UTC or GMT in Java

Php – How to get the current date and time in PHP

Related Topic