Wednesday, December 29, 2010

Timezones, timezones and a new time zone library

I've had a bit of a thing about time zones and daylights savings rules for quite some time i.e. they interest me. This was first apparent in an application I wrote for the Palm OS originally named Time Traveler (which became Titan Class). Its time zone database was inspired by zoneinfo, but was no where near as sophisticated. The Palm OS was without time zone support in its first few incarnations. Eventually time zone support was incorporated but IMHO it was weak. I digress a little... the point is I've really liked the zoneinfo database that underpins most Unix based platforms for quite some time.

Java supports zoneinfo in its implementation by use of the ICU library. There is also a JSR that's about 3 years old which aims to provide greater support for zoneinfo.

I recently had a need to ensure that my application had the latest time zone rules available. From a Java perspective, Sun or Apple (or whoever) provide a patch when time zone rules change. You then typically restart your application. I didn't want that. My goals were:

  • to have the latest rules on a monthly basis; and
  • to be able to dynamically update the time zones without having to restart my application.

JSR-310 could probably help me out here but I had another nagging concern; in fact a couple:

  • the JSR is 3 years old and doesn't appear to have progressed; and
  • I like the zoneinfo structure and wanted to use something that honoured its structure closely.

I might be a little unfair toward JSR-310 and if it becomes approved then it'll be difficult to avoid. I'm also strongly aware of the "Not Invented Here" syndrome... not my style though. Then, there's the JCP-is-dead thingy...

So, what I've done is created a new Java time zone library that takes zoneinfo files and produces a JDK compatible facade. The library uses ANTLR to parse the zoneinfo files thus actually providing a parser that can be used for many languages. I'll shortly be open-sourcing this library and probably at The Codehaus depending on how well it is received there. Meanwhile here is an overview of its structure:

Zoneinfo TZ.png

The library is effectively done and has reasonable test coverage. I hope that you'll join me and help improve it. Meanwhile any thoughts and ideas are most welcome.

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