java 当 AutoCloseable 为空时尝试使用资源
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Try-With Resource when AutoCloseable is null
提问by flakes
How does the try-with feature work for AutoCloseablevariables that have been declared null?
try-with 功能如何AutoCloseable对已声明的变量起作用null？
I assumed this would lead to a null pointer exception when it attempts to invoke closeon the variable, but it runs no problem:
我认为这在尝试调用close变量时会导致空指针异常，但它运行没有问题：
try (BufferedReader br = null){
System.out.println("Test");
}
catch (IOException e){
e.printStackTrace();
}
回答by Andy Thomas
The Java Language Specification specifies that it is closed only if non-null, in section 14.20.3. try-with-resources:
Java 语言规范在第14.20.3节中指定仅在非 null 时才关闭它。尝试资源：
A resource is closed only if it initialized to a non-null value.
资源仅在初始化为非空值时才关闭。
This can actually be useful, when a resource might present sometimes, and absent others.
这实际上很有用，当资源有时可能存在而其他资源可能不存在时。
For example, say you might or might not have a closeable proxy to some remote logging system.
例如，假设您可能有也可能没有某个远程日志系统的可关闭代理。
try ( IRemoteLogger remoteLogger = getRemoteLoggerMaybe() ) {
if ( null != remoteLogger ) {
...
}
}
If the reference is non-null, the remote logger proxy is closed, as we expect. But if the reference is null, no attempt is made to call close() on it, no NullPointerException is thrown, and the code still works.
如果引用为非空，则远程记录器代理关闭，正如我们所期望的。但是，如果引用为空，则不会尝试对其调用 close()，也不会抛出 NullPointerException，并且代码仍然有效。
