JDK6 中的 TimeZone.setDefault 更改

2022-01-16 00:00:00 default timezone java jdk1.6 jdk1.5

我刚刚注意到 JDK 6 设置默认 TimeZone 的方法与 JDK5 不同.

I just noticed that JDK 6 has a different approach to setting a default TimeZone than JDK5.

以前，新的默认值将存储在线程局部变量中.使用 JDK6(我刚刚查看了 1.6.0.18)，实现发生了变化，因此如果用户可以写入user.timezone"属性，或者如果没有安装 SecurityManager，则时区会在 VM 范围内更改！否则会发生线程局部变化.

Previously the new default would be stored in a thread-local variable. With JDK6 (I just reviewed 1.6.0.18) the implementation has changed, so that if the user can write to the "user.timezone" property, or if there is no SecurityManager installed, the timezone changes VM-wide! Otherwise a thread-local change occurs.

我错了吗?这似乎是一个相当大的变化，我在网上找不到任何关于它的信息.

Am I wrong? This seems to be quite a drastic change, and I couldn't find anything on the web about it.

这里是JDK6代码:

 private static boolean hasPermission() {
  boolean hasPermission = true;
  SecurityManager sm = System.getSecurityManager();
  if (sm != null) {
   try {
    sm.checkPermission(new PropertyPermission("user.timezone", "write"));
   } catch (SecurityException e) {
    hasPermission = false;
   }
  }
  return hasPermission;
 }

 /**
  * Sets the <code>TimeZone</code> that is
  * returned by the <code>getDefault</code> method.  If <code>zone</code>
  * is null, reset the default to the value it had originally when the
  * VM first started.
  * @param zone the new default time zone
  * @see #getDefault
  */
 public static void setDefault(TimeZone zone)
 {
  if (hasPermission()) {
   synchronized (TimeZone.class) {
    defaultTimeZone = zone;
    defaultZoneTL.set(null);
   }
  } else {
   defaultZoneTL.set(zone);
  }
 }

之前(在 JDK5 中)它只是:

while before (in JDK5) it was simply:

 /**
  * Sets the <code>TimeZone</code> that is
  * returned by the <code>getDefault</code> method.  If <code>zone</code>
  * is null, reset the default to the value it had originally when the
  * VM first started.
  * @param zone the new default time zone
  * @see #getDefault
  */
 public static synchronized void setDefault(TimeZone zone)
 {
  defaultZoneTL.set(zone);
 }

推荐答案

搜索bug数据库其实是个好主意:)

Searching the bugs database was actually quite a good idea :)

http://bugs.sun.com/view_bug.do?bug_id=6352812

还有(重新文档):

http://bugs.sun.com/view_bug.do?bug_id=6181786

总结:JDK 1.5 是该规则的一个例外，JDK 1.6 一切都恢复了正常"，根据文档，时区更改是 VM 范围内的.

Summary: JDK 1.5 was an exception to the rule, with JDK 1.6 things are back to 'normal', which, according to the docs, is that a timezone change is VM wide.

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