How to get the class's annotation by reflection

1

 

import java.lang.annotation.RetentionPolicy

import java.lang.annotation.Retention

import kotlin.reflect.KFunction1


Retention(RetentionPolicy.RUNTIME)

annotation class special(val why: String)


open class Model(val str: String) {

  open fun print() {

  println(str)

  }

}


special(“Mode 1 annotation”)

open class Model1(str: String) : Model(str)


special(“Mode 2 annotation”)

open class Model2(str: String) : Model(str)


class Factory(val func: KFunction1<String, Model>) {

  fun gen(): Model? {


  &nbsp;&nbsp;// Can't get the Model's special annotation, how to get it?
  &nbsp;&nbsp;val str = func.javaClass.getAnnotation(javaClass&lt;special&gt;())?.why?:"error: $func"

  &nbsp;&nbsp;return func.invoke(str)



  }

}


fun main(args: Array<String>) {

  Factory(::Model1).gen()?.print()

  Factory(::Model2).gen()?.print()

}

2

You're trying to load annotations of an anonymous declaration synthesized for ::ModelN expression, instead of the desired class.

Right now I can only suggest you additionally to pass an instance of Class you’re creating to Factory. In the future func will be a KConstructor and it will be possible to obtain this information from it alone.

3

 

class Factory(val cls: Class<out Model>) {

  fun gen(): Model? {


  &nbsp;&nbsp;val str = cls.getAnnotation(javaClass&lt;special&gt;())?.why ?: "error: ${cls}"

  &nbsp;&nbsp;return cls.getConstructor(javaClass&lt;String&gt;()).newInstance(str)



  }

}


fun main(args: Array<String>) {

  Factory(javaClass<Model1>()).gen()?.print()

  Factory(javaClass<Model2>()).gen()?.print()

}


I see, Is there a better way?