loading regular/directory resources via classloader

[Alan Bateman]

On 12/06/2024 08:18, Robert Scholte wrote:
>
> When running this using the classpath or modulepath I’ll get true for 
> every line.
>
> However, when creating the application with jlink, only regular 
> resources return true(i.e. the second and fourth log statement), the 
> “directories” return false.
>
> Is this difference intended behavior?
>
>

The parameter provided to getResource is a resource name. The 
getResource/getResourceAsStream methods don't specify if "directories" 
are located as resources with that method. ModuleReader is the only 
class (that I can think of) that set expectations on this.

When exploded on the file system then there is a sensible mapping. This 
means using the resource name 
"META-INF/micronaut/io.micronaut.inject.BeanDefinitionReference" and 
"META-INF/micronaut/io.micronaut.inject.BeanDefinitionReference/" will 
return a file URL to the directory. Whether getResourceAsStream returns 
a useful InputStream is another question as it's highly platform 
specific if you can open a directory as a regular file.

For JAR files then it depends on whether the JAR file has entries for 
directories. JAR files are based on the ZIP format and some tooling will 
create JAR files that don't have entries for directories (they aren't 
needed). So depending on what created the JAR file then getResource 
method may return a jar URL to a "directory entry" or it may return null.

For modules in a a run-time image then there isn't the equivalent of 
directories so #2 and #4 returning null is expected. It would be 
technically feasible to synthesize entries to have this work in many 
more cases, but not clear if it's worth doing. We should at least 
surface expectations in the Class/ClassLoader.getResourceXXX API docs as 
the notion of "resource" has never been clearly specified.

-Alan
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