CODEWITHSUNDEEP
javaresources
Rafael Winterhalter
Rafael Winterhalter

Reputation: 43987

getResourceAsStream returning null after it had worked

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.

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.

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

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

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

Any ideas?

Upvotes: 1

Views: 304

Answers (1)

Rafael Winterhalter
Rafael Winterhalter

Reputation: 43987

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;
    }
}

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...

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

Upvotes: 1

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