ClassLoader API to look up class files

[Alan Bateman]

On 22/09/2024 17:45, Rafael Winterhalter wrote:
> That is only true for Class::getResource which resolves resources 
> relative to the loaded class's class file location. Java agents 
> typically use ClassLoader::getResource(AsStream) as the loaded class 
> is not available in the general case of transforming, and not 
> retransforming, a class. For example, when instrumenting a newly 
> loaded class A in a ClassFileTransformer, it might not be the case 
> that its superclass B is loaded. If class B exists in two versions as 
> part of a multi-release jar file, currently, you need to query the 
> class loader of A as the JVM would do. When loading a class, 
> ClassLoader::findClass respects the multi-release characteristic. But 
> for ClassLoader::getResource, this is not the case. This is why I want 
> to suggest a new method where this is possible, as the intend to 
> resolve a class file is explicit. Currently, you need to iterate as 
> the ClassLoader does not expose any relevant information.

If a URLClassLoader is created with a URL to a JAR file then it should 
open it as a MR-JAR and getResource should find the .class resources in 
the versioned section. Are you saying that this doesn't work? If it 
doesn't work then I think it would be useful to show the 
getResource(name) output. If the resource is versioned then you end with 
"!/META-INF/versions/$N/$R". But maybe this is a different type of 
ClassLoader?

-Alan