Utils to get implementation classes of an interface

ReflectionUtils.kt

/**
 * Kotlin version of https://dzone.com/articles/get-all-classes-within-package
 * Mentioned here as well: https://stackoverflow.com/a/520344/798165
 */
object ReflectionUtils {

    /**
     * Returns list of classes if interface is located in the same package with implementations
     */
    @Suppress("UNCHECKED_CAST")
    fun <T> getImplementationsOfThePackage(requiredInterface: Class<T>): List<Class<T>> {
        val name = requiredInterface.`package`!!.name
        val result = mutableListOf<Class<T>>()

        val classes = getClasses(name)
        classes.forEach { clazz ->
            val interfaces = clazz.interfaces
            interfaces.forEach {
                if (requiredInterface == it) {
                    result.add(clazz as Class<T>)
                }
            }
        }

        return result
    }

    fun getClasses(packageName: String): List<Class<*>> {
        val classLoader = Thread.currentThread().contextClassLoader!!
        val path = packageName.replace('.', '/')
        val resources = classLoader.getResources(path)
        val dirs = mutableListOf<File>()
        while (resources.hasMoreElements()) {
            val resource = resources.nextElement()
            dirs.add(File(resource.file))
        }
        val classes = mutableListOf<Class<*>>()
        for (directory in dirs) {
            classes.addAll(findClasses(directory, packageName))
        }
        return classes
    }

    fun findClasses(
        directory: File,
        packageName: String
    ): List<Class<*>> {
        val classes = mutableListOf<Class<*>>()
        if (!directory.exists()) {
            return classes
        }
        val files = directory.listFiles()
        for (file in files) {
            if (file.isDirectory) {
                assert(!file.name.contains("."))
                classes.addAll(findClasses(file, packageName + "." + file.name))
            } else if (file.name.endsWith(".class")) {
                classes.add(
                    Class.forName(
                        packageName + '.' + file.name.substring(0, file.name.length - 6)
                    )
                )
            }
        }
        return classes
    }
}