Kotlin classes cannot be found when reflecting filepaths to source directories or jars - reflection

Question

===Update: Using org.reflections:reflections:0.9.11
Looking to use the following line to pull a list of class names from Kotlin source...
Reflections.getSubTypesOf(Any::class.java)
However I receive a message that Kotlin class files aren't being seen when I run the following script...
val classLoader = URLClassLoader(this.getDirectoryUrls(), null)
println("retrieved class loader")
val config = getConfig(classLoader)
println("retrieved source config")
val reflections = Reflections(config)
println("retrieved reflections")
// For 3 paths: Reflections took 3 ms to scan 3 urls, producing 0 keys and 0 values
=== Update: The 3 urls added by "getDirectoryUrls()" are directories containing kotlin class source files.
Below is my config... ideas?
private fun getConfig(classLoader: ClassLoader): ConfigurationBuilder {
val config = ConfigurationBuilder().setUrls(ClasspathHelper.forClassLoader(classLoader))
// .setScanners(SubTypesScanner(false), ResourcesScanner())
if (!packagePath.isNullOrBlank()){
System.out.println("looking in package [$packagePath]")
config.filterInputsBy(FilterBuilder().include(FilterBuilder.prefix(packagePath)))
}
config.addClassLoader(classLoader)
config.setScanners(SubTypesScanner(), TypeAnnotationsScanner())
return config
}

Answer 1

Setting SubTypesScanner(false) seems to be required to get any types with getSubTypesOf(Any::class.java) (that parameter itself stands for excludeObjectClass). Looking at the bytecode of Kotlin classes you immediately see, that they are actually looking the same as Java classes. There is no Any-superclass there. Note that Kotlins Any is actually also in other means very similar to Javas Object (but not the same, check also the following answer to 'does Any == Object'). So, we need to include the Object-class when scanning for subtypes of Any (i.e. excludeObjectClass=false).
Another problem could be the setup of your URL array. I just used the following to setup the reflections util:
val reflections = Reflections(ConfigurationBuilder()
.addUrls(ClasspathHelper.forPackage("my.test.package"))
.setScanners(TypeAnnotationsScanner(), SubTypesScanner(false)))
which will resolve all matching subtypes and will return subtypes also for Any.
reflections.getSubTypesOf(MyCustomSuperType::class.java).forEach(::println)
reflections.getSubTypesOf(Any::class.java).forEach(::println)
Analysing further: you mention "Kotlin class source files"... if that means you are pointing to the directory containing the .kt-files, then that is probably your problem. Try to use the directory which contains the .class-files instead. Moreover, ensure that the classes are on the classpath.
Maybe you know already, maybe not? Note also that if you have a (classes) directory, say /sample/directory, which is on the classpath and which contains a package, say org.example (which corresponds to the folder structure org/example or full path /sample/directory/org/example) then you must ensure that you add an URL similar to the following:
YourClass::class.java.classLoader.getResource("")
and not:
YourClass::class.java.classLoader.getResource("org.example")
// nor:
YourClass::class.java.classLoader.getResource("org/example")
You basically require the "base" directory (in the example /sample/directory or from the view of the classloader just "")) where to lookup the packages and not the package itself. If you would supply one of the latter URLs, only classes that are in the default package (within /sample/directory/org/example) would actually be found, which however is a rather uncommon setup.