java - GWT DateTimeFormat 反转时区值

Question

考虑以下代码在 GWT 中运行:

import com.google.gwt.i18n.client.DateTimeFormat;
...
DateTimeFormat fullDateTimeFormat = DateTimeFormat.getFullDateTimeFormat();
Log.info(fullDateTimeFormat.format(date, TimeZone.createTimeZone(-120)));
Log.info(fullDateTimeFormat.format(date, TimeZone.createTimeZone(0)));
Log.info(fullDateTimeFormat.format(date, TimeZone.createTimeZone(180))); 

假设现在是格林威治时间 16:00。

为什么我会得到以下输出？

Monday, February 21, 2011 6:00:00 PM Etc/GMT-2
Monday, February 21, 2011 4:00:00 PM Etc/GMT
Monday, February 21, 2011 1:00:00 PM Etc/GMT+3

预期的是

Monday, February 21, 2011 2:00:00 PM Etc/GMT-2
Monday, February 21, 2011 4:00:00 PM Etc/GMT
Monday, February 21, 2011 7:00:00 PM Etc/GMT+3

什么是正确的修复方法？

Answer 1

“Etc/GMT-2”实际上(非常令人惊讶)是“+02:00”，参见 http://en.wikipedia.org/wiki/Tz_database#Area :

In order to conform with the POSIX style, those zones beginning with "Etc/GMT" have their sign reversed from what most people expect. In this style, zones west of GMT have a positive sign and those east have a negative sign.

您的代码在我的机器上导致不同的输出(可能是因为我的语言环境不同):

Monday, 2011 February 21 18:00:00 UTC+2
Monday, 2011 February 21 16:00:00 UTC
Monday, 2011 February 21 13:00:00 UTC-3

所以，负责反转的不是DateTimeFormat，而是TimeZone.createTimeZone(int timeZoneOffsetInMinutes)!

---

让我们进一步了解 com.google.gwt.i18n.client.TimeZone 的 GWT javadoc:

getOffset(Date 日期):

* Returns the RFC representation of the time zone name for the given date.
* To be consistent with JDK/Javascript API, west of Greenwich will be
* positive.

和composeGMTString(int offset):

* In GMT representation, +/- has reverse sign of time zone offset.
* when offset == 480, it should output GMT-08:00.