1ºDay夏令时Java和JS表现出不同的行为 [英] 1º Day of Daylight Saving Time Java and JS showing a different behavior

问题描述

假设巴西利亚GMT -0300：DST于2012年10月21日00:00:00，应将时钟提前一小时

Assuming Brasilia GMT -0300: DST on 21/10/2012 at 00:00:00, when the clock should be advanced by one hour

Java

new Date(2012 - 1900, 9, 21, 0, 0, 0)
Sun Oct 21 01:00:00 BRST 2012

Chrome / FireFox（控制台）

Chrome/FireFox (console)

new Date(2012, 9, 21, 0, 0 ,0)
Sat Oct 20 2012 23:00:00 GMT-0300 (Hora oficial do Brasil)

Java中的结果是我所期望的，但是JS中的结果我无法理解。我发现了这个发布其中bjornd说

The result in Java is what I was expecting, but the result in JS I can not understand. I found this post where bjornd says

这是绝对正确的行为

This is an absolutely correct behavior

，但没有解释为什么这种行为可以。

but didn't explain why this behavior is OK.

我的问题是：

为什么JS过去一小时返回日期？

PS我知道日期已标记为弃用，但我使用的是GWT；日期是我唯一的选择。

P.S. I know Date is marked for "deprecation", but I'm using GWT; Date is my only option.

推荐答案

基本上，就我所知，答案是错误的。甚至我也不完全满意Java版本。

Basically, that answer was incorrect as far as I can see. I'm not entirely happy with the Java version, even.

从根本上说，您正在尝试构造一个从未发生过的本地日期/时间。从本地时间转换为UTC总是很棘手，因为存在三种可能性：

Fundamentally, you're trying to construct a local date/time which never happened. Translating from local time to UTC is always tricky, as there are three possibilities:

• 明确的映射，在大多数时区都是这样每年除两个小时外的所有时间


• 在向后过渡期间，在同一时间段两次出现相同的映射（例如，当地时间上午12:59，凌晨1点） ，... 1:59 am、1am、1:59am、2am）


• 空白映射，其中根本不存在本地时间段（例如，本地时间为12:59 am ，凌晨2点，凌晨2:01）

巴西在午夜向前移动时钟，因此当地时间实际上是：

Brazil moves its clocks forward at midnight, so local time actually goes:

October 20th 11:58pm
October 20th 11:59pm
October 21st 01:00am
October 21st 01:01am

您要求的当地时间从未发生过。看起来Java只是假设您想将其向前滚动...而JavaScript却变得混乱:(如果您在2013年2月16日开始时要求午夜，则JavaScript结果更容易理解（但仍然不正确），例如-时钟将在15日回到晚上11点，而16日在凌晨12点是明确的，因为它只能在15日的第二 11 pm-11:59pm之后发生。

The local time you've asked for simply never happened. It looks like Java is just assuming you want to roll it forward... whereas JavaScript is getting confused :( The JavaScript result would be more understandable (but still incorrect) if you were asking for midnight at the start of February 16th 2013, for example - where the clocks would have gone back to 11pm on the 15th. 12am on the 16th is unambiguous, as it can only happen after the "second" 11pm-11:59pm on the 15th.

好的日期/时间API（在我看来非常偏颇的观点）会迫使您说出在进行转换时想要如何产生歧义和空白。

A good date/time API (in my very biased view) would force you to say how you want to happen ambiguity and gaps when you do the conversion.

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