问题
I am trying to generate some code using Java annotation processing tools, I have nested annotations where the parent annotation value is an array of the child annotation, and the child annotation value is an array of classes.
Annotations:
public @interface ParentAnnotation {
ChildAnnotation[] value();
}
public @interface ChildAnnotation {
Class<?>[] value();
}
Usage:
@ParentAnnotation(
{
@ChildAnnotation({Foo.class, Bar.class}),
@ChildAnnotation({Goo.class, Doo.class})
})
public class Sample{
}
calling value() on the annotation with my Processor subtype fails with this exception:
Error:java: error while creating source file javax.lang.model.type.MirroredTypeException: Attempt to access Class object for TypeMirror org.dominokit.samples.layout.shared.extension.LayoutEvent
at com.sun.tools.javac.model.AnnotationProxyMaker$MirroredTypeExceptionProxy.generateException(AnnotationProxyMaker.java:308)
at sun.reflect.annotation.AnnotationInvocationHandler.invoke(AnnotationInvocationHandler.java:84)
at com.sun.proxy.$Proxy28.value(Unknown Source)
at org.dominokit.domino.apt.client.processors.module.client.presenters.PresenterProxySourceWriter.generateFireActivationEvent(PresenterProxySourceWriter.java:238)
at org.dominokit.domino.apt.client.processors.module.client.presenters.PresenterProxySourceWriter.asTypeBuilder(PresenterProxySourceWriter.java:64)
at org.dominokit.domino.apt.client.processors.module.client.presenters.PresenterProxyProcessingStep.generateProxy(PresenterProxyProcessingStep.java:66)
at org.dominokit.domino.apt.client.processors.module.client.presenters.PresenterProxyProcessingStep.process(PresenterProxyProcessingStep.java:53)
at org.dominokit.domino.apt.client.processors.module.client.presenters.PresenterProxyProcessor.process(PresenterProxyProcessor.java:61)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor(JavacProcessingEnvironment.java:794)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:705)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1800(JavacProcessingEnvironment.java:91)
at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1035)
at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1176)
at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)
at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)
at com.sun.tools.javac.main.Main.compile(Main.java:523)
at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)
at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)
at org.jetbrains.jps.javac.JavacMain.compile(JavacMain.java:196)
at org.jetbrains.jps.incremental.java.JavaBuilder.compileJava(JavaBuilder.java:448)
at org.jetbrains.jps.incremental.java.JavaBuilder.compile(JavaBuilder.java:318)
at org.jetbrains.jps.incremental.java.JavaBuilder.doBuild(JavaBuilder.java:243)
at org.jetbrains.jps.incremental.java.JavaBuilder.build(JavaBuilder.java:201)
at org.jetbrains.jps.incremental.IncProjectBuilder.runModuleLevelBuilders(IncProjectBuilder.java:1327)
at org.jetbrains.jps.incremental.IncProjectBuilder.runBuildersForChunk(IncProjectBuilder.java:1007)
at org.jetbrains.jps.incremental.IncProjectBuilder.buildTargetsChunk(IncProjectBuilder.java:1074)
at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunkIfAffected(IncProjectBuilder.java:968)
at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunks(IncProjectBuilder.java:797)
at org.jetbrains.jps.incremental.IncProjectBuilder.runBuild(IncProjectBuilder.java:375)
at org.jetbrains.jps.incremental.IncProjectBuilder.build(IncProjectBuilder.java:178)
at org.jetbrains.jps.cmdline.BuildRunner.runBuild(BuildRunner.java:138)
at org.jetbrains.jps.cmdline.BuildSession.runBuild(BuildSession.java:302)
at org.jetbrains.jps.cmdline.BuildSession.run(BuildSession.java:135)
at org.jetbrains.jps.cmdline.BuildMain$MyMessageHandler.lambda$channelRead0$0(BuildMain.java:229)
at org.jetbrains.jps.service.impl.SharedThreadPoolImpl.lambda$executeOnPooledThread$0(SharedThreadPoolImpl.java:42)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
so how i can read these classes from the annotation as a List<TypeMirror> ?
回答1:
After lots of debugging and trying one thing at a time i found the solution for this, the idea was in how to use the AnnotationMirror to obtain AnnotationValue, there was some sort of confusion at some point where the expected return types to be AnnotationValue[] was actually List<AnnotationValue>, below is a utility method i wrote to read the classes as a List<List<TypeMirror>> :
private List<List<TypeMirror>> getNestedAnnotationClassesValue(Element element){
List<List<TypeMirror>> classesInAnntation = new ArrayList<>();
if (nonNull(element.getAnnotation(ParentAnnotation.class))) {
List<? extends AnnotationMirror> annotations = element.getAnnotationMirrors();
for (AnnotationMirror annotationMirror : annotations) {
if (types.isSameType(annotationMirror.getAnnotationType(), elements.getTypeElement(ParentAnnotation.class.getName()).asType())) {
Map<? extends ExecutableElement, ? extends AnnotationValue> elementValues = annotationMirror.getElementValues();
elementValues.values()
.stream()
.findFirst()
.ifPresent(annotationValue -> {
List<AnnotationMirror> childAnnotations = (List<AnnotationMirror>) annotationValue.getValue();
childAnnotations.stream()
.forEach(childAnnotationMirror -> {
Collection<? extends AnnotationValue> values = childAnnotationMirror.getElementValues()
.values();
AnnotationValue childAnnotationValue = values.stream().findFirst().get();
List<AnnotationValue> classesInNestedAnnotation = (List<AnnotationValue>) childAnnotationValue.getValue();
Iterator<? extends AnnotationValue> iterator = classesInNestedAnnotation.iterator();
List<TypeMirror> typeMirrorsInNestedAnnotation = new ArrayList<>();
while (iterator.hasNext()) {
AnnotationValue next = iterator.next();
typeMirrorsInNestedAnnotation.add((TypeMirror) next.getValue());
}
if (!typeMirrorsInNestedAnnotation.isEmpty()) {
classesInAnntation.add(typeMirrorsInNestedAnnotation);
}
});
});
}
}
}
return classesInAnntation;
}
来源：https://stackoverflow.com/questions/54441572/how-to-read-a-class-values-from-a-nested-annotation-in-an-annotation-processor