java - 这段 Java Puzzlers 代码有什么问题？

Question

在新的第三版 Effective Java 中，Joshua Bloch 提到了来自 Java Puzzlers 的一段代码(它是关于在 try-finally 中关闭资源):

For starters, I got it wrong on page 88 of Java Puzzlers, and no one noticed for years. In fact, two-thirds of the uses of the close method in the Java libraries were wrong in 2007.

但我不确定这里哪一部分是错误的？

} finally {
  if (in != null) {
    try {
      in.close();
    } catch (IOException ex) {
      // There is nothing we can do if close fails
    }
  }
  if (out != null) {
    try {
      out.close();
    } catch (IOException ex) {
      // Again, there is nothing we can do if close fails
    }
  }
}

这是此代码的新版本:

try {
  OutputStream out = new FileOutputStream(dst);
  try {
    byte[] buf = new byte[BUFFER_SIZE];
    int n;
    while ((n = in.read(buf)) >= 0) out.write(buf, 0, n);

  } finally {
    out.close();
  }
} finally {
  in.close();
}

Answer 1

如果 in.close() 抛出未被 catch block 捕获的异常(例如任何 RuntimeException)，out 将不会甚至试图关闭。

虽然在给定的示例中(对于最有可能出现 IOException 的普通流)这不是一个大问题，但代码不正确并且学习这样编写它可能会导致更严重的问题路。