How to obtain all subclasses of a given sealed class?

Question

Recently we upgraded one of our enum class to sealed class with objects as sub-classes so we can make another tier of abstraction to simplify code. However we c

Answer 1

A wise choice is using ServiceLoader in kotlin. and then write some providers to get a common class, enum, object or data class instance. for example:

val provides = ServiceLoader.load(YourSealedClassProvider.class).iterator();

val subInstances =  providers.flatMap{it.get()};

fun YourSealedClassProvider.get():List{/*todo*/};

the hierarchy as below:

                Provider                    SealedClass
                   ^                             ^
                   |                             |
            --------------                --------------
            |            |                |            |
        EnumProvider ObjectProvider    ObjectClass  EnumClass
            |            |-------------------^          ^
            |                                     |
            |-------------------------------------------|
                                 

---

Another option, is more complicated, but it can meet your needs since sealed classes in the same package. let me tell you how to archive in this way:

1. get the URL of your sealed class, e.g: ClassLoader.getResource("com/xxx/app/YourSealedClass.class")
2. scan all jar entry/directory files in parent of sealed class URL, e.g: jar://**/com/xxx/app or file://**/com/xxx/app, and then find out all the "com/xxx/app/*.class" files/entries.
3. load filtered classes by using ClassLoader.loadClass(eachClassName)
4. check the loaded class whether is a subclass of your sealed class
5. decide how to get the subclass instance, e.g: Enum.values(), object.INSTANCE.
6. return all of instances of the founded sealed classes