ClassLoader can't solve directories on Graal binary

[mageddo]

Context

I'm using embedded flyway to automatically migrate my database scripts and it solves directories on classpath to load sql files

What is expected

java.lang.ClassLoader#getResources(String) returns the URL for the specified directory

What is happening

java.lang.ClassLoader#getResources(String) returns an empty Enumeration

Steps to reproduce

Here an example project reproducing the issue

App.java

public static void main(String[] args) throws Exception {
	System.out.println(getResources("folder/subfolder"));
	System.out.println(getResources("folder/subfolder/resource-001.txt"));
}

public static List<URL> getResources(String name) throws IOException {
	final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
	return Collections.list(classLoader.getResources(name));
}

$ ./gradlew clean build nativeImage && ./build/graal/resources-resolution
[]
[resource:folder/subfolder/resource-001.txt]

[guanchao-yang]

@olpaw Which version do we plan to release ? Thank you very much

[olpaw]

@guanchao-yang, @mageddo as of now (GraalVM 19.1.1) we only support adding resources that are real data files to native-images. A directory on its own is not seen as a resource because we cannot embed a directory into a native-image. If we'd add support for that, which kind of usage patterns would need to be supported on resources that represent directories to make spring work as expected?

[dsyer]

which kind of usage patterns would need to be supported on resources that represent directories to make spring work as expected?

It's nothing really to do with Spring. The question above was about Flyway, where they sort the filenames in a directory and execute them as scripts in order. Webjars also likes to traverse "directories" in classpath resources (so it can resolve the "best" available resource matching the request). It's just a common pattern, to search for stuff in packages and subpackages.

Here's a library dedicated to scanning classpath directories: https://github.com/classgraph/classgraph. It's used by the most recent versions of webjars, and naturally doesn't work in substratevm because of the above.

[rtfpessoa]

Any progress here? Are there any workarounds we can do to list all files in a directory or in the classpath in general?