Create java.util.Date from C# System.TimeZone

Question

I have a Java service which needs to return date/time information that is formatted relative to a user's current timezone (C#). For example, say a user is on the west coast (pacific time) where it is 8:00pm. They connect to a service that is hosted in the midwest (central time) where it is 10:00pm. If the user were to ask the server for the current time, the server should respond, "8:00pm" for the user.

My thought is that the client application (C#) will pass information to the service about its current timezone or UTC offset. Java will then create/format all dates using that timezone.

However, I am having trouble finding a good way to pass C# System.TimeZone information in a way where Java can create and use a java.util.TimeZone object. I can get the UTC offset from C# but not a three digit timezone code. In Java I can create a TimeZone from a three digit code but can't find a way to create one from a UTC offset. From everything I've seen in Java, TimeZones are created with a code ("PST") or country/region ("America/Los_Angeles"), and I don't believe there is a clear way to get the timezone in this format in C#.

How might this be accomplished?

Unfortunately no. In this scenario, the view for the client is being generated/rendered on the server. — trebor, Dec 02 '15 at 14:08

score 0 · Answer 1 · edited May 23 '17 at 11:44

Work In UTC

As the comment suggested, usually the best way to go is to work your business logic in UTC. Adjust into a local time zone only for presentation when expected by a user.

So your Java backend should be returning a UTC date-time value. Usually the best way to do that is to serialize the date-time value as a string in the standard ISO 8601 format. Then let the client app handle the presentation by generating a string representation of the date-time value adjusted into a particular time zone.

See this Question about best practices for date-time work.

But somehow this is not feasible in the context of this Question. So the client app needs to communicate to the backend the desired/expected time zone.

Time Zone

Avoid the 3-4 letter codes such as EST or IST. These codes are neither standardized nor unique. Furthermore they invoke Daylight Saving Time in a confusing way.

Instead use official time zone names. These are mostly in the format of "continent", slash, and "region/city" in English, such as America/Montreal or Asia/Kolkata.

.Net Fails To Support Proper Time Zone Naming

Unfortunately, it looks like the .Net team did not know about proper time zone naming.

The System.TimeZone class offers properties such a StandardName. But the examples in the System.TimeZone doc show "Pacific Standard Time" rather than a proper name such as "America/Los_Angeles".

Noda Time

My first suggestion is to consider using the Noda Time project, an alternative date and time API for .NET. It was inspired by the highly successful Joda-Time library in Java, which in turn inspired the new java.time framework built into Java 8 and later.

Looks like Noda Time has support for proper time zones. Rather than use System.TimeZone, use Noda Time to obtain the time zone information.

Roll Your Own Mapping

If Noda Time is not an option, then I might look to see if my users are all in a few time zones. If so, I would make my own mapping of such as "Pacific Daylight Time" returned by C# the standard name for a time zone being the proper name "America/Los_Angeles".