kotlin - Kotlin通过反射读取属性注释

Question

我已经为属性创建了一个注释，现在我想在运行时通过反射读取它。我认为我所做的一切正确，但是没有注释。

为什么注释不可用？

@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.PROPERTY, AnnotationTarget.VALUE_PARAMETER)
annotation class MyAnnotation

class MyClass(@MyAnnotation val attr: List<String>)

fun main(args: Array<String>) {
    var prop = MyClass::attr
    prop.annotations.forEach { println("prop.annotations -> " + it) }
    prop.javaClass.getAnnotations().forEach { println("prop.javaClass.getAnnotations -> " + it) }
    println("isAnnotationPresent -> ${prop.javaClass.isAnnotationPresent(MyAnnotation::class.java)}")
}

输出:
prop.javaClass.getAnnotations-> @ kotlin.Metadata(xi = 0，bv = [1，0，3]，mv = [1，1，16]，k = 3，xs =，d1 = []，d2 = []，pn =)
isAnnotationPresent->否

Answer 1

您可以将其指定为@Target(AnnotationTarget.PROPERTY, AnnotationTarget.VALUE_PARAMETER)并按以下方式访问，而不必将注释目标指定为@Target(AnnotationTarget.FIELD):

@Target(AnnotationTarget.FIELD)
annotation class MyAnnotation

class MyClass(@MyAnnotation val attr: String)

fun main(args: Array<String>) {
    val prop = MyClass::attr
    println("Is MyAnnotation annotated - ${prop.javaField?.isAnnotationPresent(MyAnnotation::class.java)}")
    prop.javaField?.annotations?.forEach { println("Annotation present is - ${it.annotationClass.qualifiedName}") }
}

输出:

Is MyAnnotation annotated - true

Annotation present is - packageName.MyAnnotation