在AOP開發(fā)中我們經(jīng)常通過Element的getAnnotation(Class<A> var1)方法去獲取自定義注解中的傳入的屬性
例如：
@Target(AnnotationTarget.FIELD)
@Retention(AnnotationRetention.SOURCE)
@MustBeDocumented
annotation class TTEventType(val value: KClass<*>)
當(dāng)我們獲取KClass<*>類型時(shí)會(huì)出現(xiàn)javax.lang.model.type.MirroredTypeException寨蹋，這是因?yàn)?/p>
The annotation returned by this method could contain an element whose value is of type Class. 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. 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. Similarly, attempting to read a Class[]-valued element will result in a MirroredTypesException.
處理一
如果硬要從getAnnotation()獲取則可以利用MirroredTypeException
public class MirroredTypeException
extends MirroredTypesException
Thrown when an application attempts to access the Class object corresponding to a TypeMirror.
從異常捕獲中獲取TypeMirror
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
}
處理二
我們從AnnotationMirror下手 在List<? extends AnnotationMirror> getAnnotationMirrors()方法中獲取:
private fun getEventTypeAnnotationMirror(typeElement: VariableElement, clazz: Class<*>): AnnotationMirror? {
val clazzName = clazz.name
for (m in typeElement.annotationMirrors) {
if (m.annotationType.toString() == clazzName) {
return m
}
}
return null
}
private fun getAnnotationValue(annotationMirror: AnnotationMirror, key: String): AnnotationValue? {
for ((key1, value) in annotationMirror.elementValues) {
if (key1!!.simpleName.toString() == key) {
return value
}
}
return null
}
private fun getMyValue(foo: VariableElement, clazz: Class<*>, key: String): TypeMirror? {
val am = getEventTypeAnnotationMirror(foo, clazz) ?: return null
val av = getAnnotationValue(am, key)
return if (av == null) {
null
} else {
av.value as TypeMirror
}
}
val typeMirror = getMyValue(variableElement,TTEventType::class.java,"value")
messager.printMessage(Diagnostic.Kind.NOTE, " --typeMirror-- $typeMirror")
參考
Getting Class values from Annotations in an AnnotationProcessor
