从静态最终变量初始值设定项获取 Logger 是否有效？

发布于 2024-12-03 12:56:37 字数 690 浏览 0 评论 0原文

我们有很多类代码，其中有一些样板代码，如下所示：

private static Logger logger = null;

private static Logger getLogger() {
  if (logger == null) {
    logger = Logger.getLogger(MyClass.class);
  }
  return logger;
}

这个想法是类可以将调试内容记录到记录器中。第一个需要记录某些内容的代码调用 getLogger() 并使记录器存在。

这种模式有一些我不喜欢的地方。首先单例 getLogger() 是不同步的，同步它，而正确的会无缘无故地给后续的每次调用带来负担。

我真的希望能够将其压缩为这样：

private static final Logger logger = Logger.getLogger(MyClass.class);

然后我可以直接引用记录器，甚至不必费心使用单例 getter。

我担心的问题是，通过这样做，即使从未调用记录器，也会在加载类时创建记录器。我有 10,000 多个奇怪的类都调用 getLogger()，那么我实际上在这里创建了多少个 Logger 实例？如果我的 log4j 属性包含一些附加程序，我只是一遍又一遍地引用同一个记录器，还是我创建了 10,000 个这样的东西？

原文

We have a lot of class code which has some boilerplate like the following:

private static Logger logger = null;

private static Logger getLogger() {
  if (logger == null) {
    logger = Logger.getLogger(MyClass.class);
  }
  return logger;
}

The idea is that the class can log debug stuff into the Logger. The first code which needs to log something invokes getLogger() and that brings the logger into existence.

There are a couple of things I don't like about this pattern. First the singleton getLogger() is not synchronized and synchronizing it, while correct would put a burden on each subsequent call for no reason.

I really want to be able to condense it down to just this:

private static final Logger logger = Logger.getLogger(MyClass.class);

Then I can just reference logger directly and not even bother with a singleton getter.

The problem I fear is that by doing this I cause a Logger to be created when the class is loaded even if the logger is never called. I have 10,000+ odd classes all calling getLogger(), so how many instances of Logger am I actually creating here? If my log4j properties contains a few appenders am I just referencing the same logger over and over, or I am I creating 10,000 of these things?

分享到QQ

分享到微博

如果你对这篇内容有疑问，欢迎到本站社区发帖提问参与讨论，获取更多帮助，或者扫码二维码加入 Web 技术交流群。

发布评论

需要登录才能够评论，你可以免费注册一个本站的账号。

锦爱 2024-12-10 12:56:37

如果您使用默认的 Log4j 配置（即默认 LoggerRepository、DefaultCategoryFactory 等），那么您将创建 10'000 个 Logger 实例。它们消耗多少内存？除了上帝和你的分析器之外没有人知道这一点。（我猜只有后一个会告诉你这一点）。

如果内存占用对于您的环境来说太大，请将 Logger 初始化移至静态内部类，如下所示：

static class LoggerHolder {
  static Logger logger = Logger.getLogger(MyClass.class);
}

private static Logger getLogger() {
  return LoggerHolder.logger;
}

这样，Logger 的实例将仅在第一个 getLogger 上创建> 打电话。（这种技术称为按需初始化持有者（IODH），它是线程安全的并且具有零同步开销）。

我可以给你一个题外话的建议吗？考虑使用 SLF4J+Logback 库。它们由同一位作者编写，并被描述为“流行 log4j 项目的继承者，继承了 log4j 的不足”。您可以在这个SO线程中阅读更多内容。

If you use the default Log4j configuration (i.e. default LoggerRepository, DefaultCategoryFactory etc.) then you will create 10'000 Logger instances. How much memory do they consume? No one except God and your Profiler knows this. (And my guess only the latter one would tell that to you).

If the memory footprint would be too much for your environment, move Logger initialization to the static inner class like this:

static class LoggerHolder {
  static Logger logger = Logger.getLogger(MyClass.class);
}

private static Logger getLogger() {
  return LoggerHolder.logger;
}

That way the instance of Logger will be only created on the first getLogger call. (This technique is known as the Initialization On Demand Holder (IODH), it is thread-safe and has zero synchronization overhead).

And may I give you one offtopic suggestion? Consider to replace Log4J with the combination of SLF4J+Logback libraries. They are written by the very same authors and described as "a successor to the popular log4j project, picking up where log4j leaves off". You can read more in this SO thread.

回复收藏 0 原文