Android 注解处理器中的MirroredTypeException异常处理

在AOP开发中我们经常通过Element的getAnnotation(Class<A> var1)方法去获取自定义注解中的传入的属性

例如：

@Target(AnnotationTarget.FIELD)
@Retention(AnnotationRetention.SOURCE)
@MustBeDocumented
annotation class TTEventType(val value: KClass<*>)

当我们获取 KClass<*>类型时会出现javax.lang.model.type.MirroredTypeException，这是因为

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.

处理一

如果硬要从getAnnotation()获取则可以利用MirroredTypeException

public class MirroredTypeException
extends MirroredTypesException

Thrown when an application attempts to access the Class object corresponding to a TypeMirror.

从异常捕获中获取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
        }

处理二

我们从AnnotationMirror下手 在List<? extends AnnotationMirror> getAnnotationMirrors()方法中获取:

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")

参考

Getting Class values from Annotations in an AnnotationProcessor