如何从注释处理器中的嵌套注释中读取Class []值 [英] How to read a Class[] values from a nested annotation in an annotation processor

问题描述

我正在尝试使用Java批注处理工具生成一些代码，我嵌套了批注，其中父批注值是子批注的数组，而子批注值是类的数组.

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.

注释:

public @interface ParentAnnotation {
    ChildAnnotation[] value();
}
public @interface ChildAnnotation {
    Class<?>[] value();
}

用法:

@ParentAnnotation(
{
      @ChildAnnotation({Foo.class, Bar.class}),
      @ChildAnnotation({Goo.class, Doo.class})
})
public class Sample{
}

使用我的Processor子类型在注释上调用value()失败，但出现以下异常:

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)

那么我如何以List<TypeMirror>的形式从注释中读取这些类?

so how i can read these classes from the annotation as a List<TypeMirror> ?

推荐答案

经过大量调试并一次尝试一件事情之后，我找到了解决方案，其思想是如何使用AnnotationMirror获取，在某些时候，期望的返回类型实际上是List<AnnotationValue>时有些混乱，下面是我编写的一种实用程序方法，用于将类读取为List<List<TypeMirror>>:

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;
    }

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