getResourceAsStream 工作后返回 null [英] getResourceAsStream returning null after it had worked

问题描述

我正在从 servlet 容器运行应用程序.此应用程序生成的信件源自与 jar 一起打包的一些文件模板.我通过 Class.getResourceAsStrem 获取了这些文件，并且该应用程序运行良好.

I am running an application from a servlet container. This application produces letters which are derived from some file templates that packed with the jar. I get hold of these files by Class.getResourceAsStrem and the application works perfectly fine.

然而，经过数千次调用，该方法突然返回null，并继续返回null，直到应用程序重新启动.我对此没有任何解释，我看不出为什么会突然发生这种情况.

However, after thousands of invocations, the method suddently returns null and continues to return null until the application is restarted. I have no explanation for this and I cannot see a reason why this would suddenly happen.

我首先认为这可能是因为未关闭的流指向相同的资源，但我在打开它后立即将流处理包装在 catch-try-block 中.此外，堆转储不会显示此类流对象，而且我认为这应该导致 IOException 代替.另外，它在javadoc中说

I first thought this might be because of unclosed streams pointing to the same resource but I am wrapping the stream processing in a catch-try-block right after opening it. Also, a heap dump does not show such stream objects and I furthermore think that this should result in an IOException instead. Also, it says in the javadoc

一个 InputStream 对象，如果没有找到同名的资源，则为 null

A InputStream object or null if no resource with this name is found

但是为什么应用程序突然无法再找到之前成功找到的资源.

But why would the application suddenly not longer be able to find a resource it successfully found before.

有什么想法吗?

推荐答案

我想我找到了原因.ClassLoader.getResourceAsStream(String) 最终委托给 Class.getResourceAsStream 的实现如下:

I think I found the reason. ClassLoader.getResourceAsStream(String) to which Class.getResourceAsStream eventually delegates is implemented like this:

public InputStream getResourceAsStream(String name) {
    URL url = getResource(name);
    try {
        return url != null ? url.openStream() : null;
    } catch (IOException e) {
        return null;
    }
}

我猜发生了 IOException 并且确实存在泄漏的打开文件.然而，这个异常被吞没了，我得到了一个 null 指针作为回报.天才 API...

I guess there is an IOException occurring and that there are indeed leaking open files. However, this exception gets swallowed and I get a null pointer in return. Genius API...

更新:在查看堆转储后，我发现应用程序代码正在泄漏文件.该死的，ClassLoader 实现，用 NullPointerExceptions 误导了我.

Update: After looking at a heap dump, I found application code that was leaking files. Damn you, ClassLoader implementation, misdirecting me with NullPointerExceptions.

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