Java - 检测 `finally` block 期间是否有异常发生

Question

我正在根据 Java 语言规范考虑这一点:

If the catch block completes abruptly for reason R, then the finally block is executed. Then there is a choice:

• If the finally block completes normally, then the try statement completes abruptly for reason R.

• If the finally block completes abruptly for reason S, then the try statement completes abruptly for reason S (and reason R is discarded).

我有一个 block 如下:

try {
  .. do stuff that might throw RuntimeException ...
} finally {
  try {
    .. finally block stuff that might throw RuntimeException ...
  } catch {
    // what to do here???
  }
}

理想情况下，我希望在 finally block 中抛出的任何 RuntimeException 能够逃逸，仅当它不会导致 RuntimeException抛出在主 try block 中并被丢弃。

Java中有什么方法可以让我知道与finally block 关联的 block 是否正常完成？

我猜我可以将一个 boolean 设置为主 try block 的最后一个语句(例如，completedNormally = true .这是最好的方法，还是有更好/更标准的方法？

Answer 1

我认为关键是不要失去最初的原因(如果有的话)。

如果我们看看 try-with-resources 的行为:

private static class SomeAutoCloseableThing implements AutoCloseable {

    @Override
    public void close() {
        throw new IllegalStateException("closing failed");
    }

}

public static void main(String[] args) {
    try (SomeAutoCloseableThing thing = new SomeAutoCloseableThing()) {
        throw new IllegalStateException("running failed");
    }
}

我们最终得到:

Exception in thread "main" java.lang.IllegalStateException: running failed
    at Main.main(Main.java:16)
    Suppressed: java.lang.IllegalStateException: closing failed
        at Main$SomeAutoCloseableThing.close(Main.java:9)
        at Main.main(Main.java:17)

这个堆栈跟踪很棒，因为我们看到了两个异常，即我们不会丢失运行失败异常。

<小时/>

不使用 try-with-resources 来实现这一点，是错误的方式:

public static void main(String[] args) {
    SomeAutoCloseableThing thing = new SomeAutoCloseableThing();
    try {
        throw new IllegalStateException("running failed");
    } finally {
        thing.close();
    }
}

我们最终得到:

Exception in thread "main" java.lang.IllegalStateException: closing failed
    at Main$SomeAutoCloseableThing.close(Main.java:9)
    at Main.main(Main.java:19)

我们不知道运行失败也发生过，因为我们破坏了控制流，如果您需要调试这样的情况，那是非常糟糕的。

<小时/>

在不使用 try-with-resources 的情况下实现这一点，正确的方式(在我看来)是“记录并忘记”finally block 中发生的异常:

public static void main(String[] args) {
    SomeAutoCloseableThing thing = new SomeAutoCloseableThing();
    try {
        throw new IllegalStateException("running failed");
    } finally {
        try {
            thing.close();
        } catch (Exception e) {
            LoggerFactory.getLogger(Main.class).error("An error occurred while closing SomeAutoCloseableThing", e);
        }
    }
}

我们最终得到:

17:10:20.030 [main] ERROR Main - An error occurred while closing SomeAutoCloseableThing
java.lang.IllegalStateException: closing failed
    at Main$SomeAutoCloseableThing.close(Main.java:10) ~[classes/:?]
    at Main.main(Main.java:21) [classes/:?]
Exception in thread "main" java.lang.IllegalStateException: running failed
    at Main.main(Main.java:18)

不如 try-with-resources 方法好，但至少我们知道实际发生了什么，没有丢失任何东西。