始终在UTC时区下运行Java应用程序

Question

以下两种方法是否完全等效，以确保 Java 应用程序在 UTC 中运行？

1. Starting the JVM with the 'user.timezone' parameter:

   java -jar MyJar.jar -Duser.timezone=UTC
   

2. Having the following method executed from the main() method (Java 8)

   private static void setUtcTimezone() {
       ZoneId zoneId = ZoneId.of("UTC");
       TimeZone zone = TimeZone.getTimeZone(zoneId);
       TimeZone.setDefault(zone);
   }
   

我希望让应用程序在UTC时间下运行，不再提供可选项，因此不建议使用JVM参数方法。

- Collin Peters

Answer 1

没有任何迹象表明这两种方法不等价。唯一的区别在于变体1在进入main()之前设置了默认时区。

因此，在调用setUtcTimezone()之后，它们两者是等价的，但在此之前不是。 理论上，您可以有一个静态初始化程序在main被调用之前使用时区。

但这由您负责。

There are no pitfalls using variant 2, use it, it will work.

I use this approach which is a bit shorter.

 TimeZone.setDefault(TimeZone.getTimeZone("UTC"));

The only weak point in both variants, is trusting that no other code changes the default time zone. So it is a good idea for specific method that should use UTC in e.g Date formatting to use a DateFormater (not static, either an instance or using Thread.Local()) and explicitly set the TimeZone UTC to that formatter. This then is save to output or calculate in UTC.

- AlexWien