[英]Kotlin - How to get KClass<*> annotation parameter from annotation processor
I have the following annotation:我有以下注释:
@Target(AnnotationTarget.CLASS)
@Retention(AnnotationRetention.SOURCE)
@MustBeDocumented
annotation class Model(
val owner: KClass<*>,
val consumer: KClass<*>
)
@Model(DataOwner::class, DataConsumer::class)
interface Student {
val name: String
val group: Group
}
I need to get the value of owner
and consumer
in my annotation processor.我需要在我的注释处理器中获取
owner
和consumer
的价值。
I've tried this approach:我试过这种方法:
private inline fun <reified T> findAnnotationValue(
element: Element,
annotationClass: KClass<*>,
valueName: String
): T? {
return element.annotationMirrors.map {
it to it.annotationType.asElement() as TypeElement
}.firstOrNull { (_, element) ->
element.qualifiedName.contentEquals(annotationClass.qualifiedName)
}?.let { (mirror, _) ->
extractValue(mirror, valueName)
}
}
private inline fun <reified T> extractValue(
annotationMirror: AnnotationMirror,
valueName: String
): T? {
return annotationMirror.elementValues.toList()
.firstOrNull { (key, _) ->
key.simpleName.contentEquals(valueName)
}?.let { (_, value) ->
value.value as T
}
}
val ownerClass: KClass<*> = findAnnotationValue(
element,
Model::class,
"owner"
)
But it gave me this error:但它给了我这个错误:
e: [kapt] An exception occurred: java.lang.ClassCastException: com.sun.tools.javac.code.Type$ClassType cannot be cast to kotlin.reflect.KClass
I also tried this:我也试过这个:
val ownerClass: KClass<*> = element.getAnnotation(Model::class.java).owner
But it gave me this error:但它给了我这个错误:
e: [kapt] An exception occurred: javax.lang.model.type.MirroredTypeException: Attempt to access Class object for TypeMirror inc.ahmedmourad.systems.tutors.domain.model.DataOwner
inc.ahmedmourad.systems.tutors.domain.model.DataOwner
is the owner
value passed to the annotation. inc.ahmedmourad.systems.tutors.domain.model.DataOwner
是传递给注解的owner
值。
So this's where i'm stuck right now, any help is appreciated.所以这就是我现在陷入困境的地方,感谢任何帮助。 Thank you!
谢谢!
Let's start with the reason the second approach doesn't work:让我们从第二种方法不起作用的原因开始:
The annotation returned by this method could contain an element whose value is of type Class.
此方法返回的注释可能包含一个元素,其值为 Class 类型。 This value cannot be returned directly: information necessary to locate and load a class (such as the class loader to use) is not available, and the class might not be loadable at all.
无法直接返回此值:定位和加载 class(例如要使用的 class 加载程序)所需的信息不可用,并且 class 可能根本无法加载。 Attempting to read a Class object by invoking the relevant method on the returned annotation will result in a MirroredTypeException, from which the corresponding TypeMirror may be extracted.
尝试通过在返回的注释上调用相关方法来读取 Class object 将导致 MirroredTypeException,从中可以提取相应的 TypeMirror。 Similarly, attempting to read a Class[]-valued element will result in a MirroredTypesException.
同样,尝试读取 Class[]-valued 元素将导致 MirroredTypesException。
which obviously applies to KClass
as well.这显然也适用于
KClass
。
So for classes in annotations you can only get a TypeMirror
(implemented in this case by Type.ClassType
, but that's an internal detail you shouldn't rely on) and not a KClass
.因此,对于注释中的类,您只能获得
TypeMirror
(在这种情况下由Type.ClassType
实现,但这是您不应该依赖的内部细节)而不是KClass
。 Either by the first approach or通过第一种方法或
inline fun <reified T : Annotation> Element.getAnnotationClassValue(f: T.() -> KClass<*>) = try {
getAnnotation(T::class.java).f()
throw Exception("Expected to get a MirroredTypeException")
} catch (e: MirroredTypeException) {
e.typeMirror
}
which can be used as可以用作
element.getAnnotationClassValue<Model> { owner }
and returns the TypeMirror
for DataOwner
.并返回
TypeMirror
的DataOwner
。
If you are using KSP then the solution can look something like this:如果您使用的是 KSP,则解决方案可能如下所示:
Using the experimental APIs and assuming the KClass you reference in the annotation is available:使用实验性 API 并假设您在注释中引用的 KClass 可用:
resolver.getSymbolsWithAnnotation("com.example.Model")
.map {
val consumerType = try {
it.getAnnotationsByType(Model::class).single().consumer
null
} catch (e: KSTypeNotPresentException) {
e.ksType
}
val consumerDeclaration = consumerType!!.declaration as KSClassDeclaration // etc
}
If you can't do this, then maintaining a KSP view of the annotation is more flexible:如果你不能这样做,那么维护注释的 KSP 视图会更灵活:
resolver.getSymbolsWithAnnotation("com.example.Model")
.map { ksAnnotated ->
val args = ksAnnotated.annotations.single {
it.shortName.asString() == "Model" && it.annotationType.resolve().declaration.qualifiedName?.asString() == "com.example.Model"
}.arguments
val consumerType = args.single { it.name?.asString() == "owner" }.value as KSType
val consumerDeclaration = consumerType.declaration as KSClassDeclaration // etc
}
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