Add support of declarative use of reflection

This commit adds a `@Reflective` annotation that can be used to declare
that the annotated element requires reflection at runtime. By default,
the annotated element is exposed but this can be customized by
specifying a dedicated `ReflectiveProcessor`.

Closes gh-28469

spring-context/src/main/java/org/springframework/context/aot/ReflectiveProcessorBeanRegistrationAotProcessor.java

@@ -0,0 +1,149 @@
+/*
+ * Copyright 2002-2022 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.context.aot;
+
+import java.lang.reflect.AnnotatedElement;
+import java.lang.reflect.Constructor;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+import java.util.function.Consumer;
+
+import org.springframework.aot.generate.GenerationContext;
+import org.springframework.aot.hint.MemberCategory;
+import org.springframework.aot.hint.ReflectionHints;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.TypeHint.Builder;
+import org.springframework.aot.hint.annotation.Reflective;
+import org.springframework.aot.hint.annotation.ReflectiveProcessor;
+import org.springframework.aot.hint.support.RuntimeHintsUtils;
+import org.springframework.beans.BeanUtils;
+import org.springframework.beans.factory.aot.BeanRegistrationAotContribution;
+import org.springframework.beans.factory.aot.BeanRegistrationAotProcessor;
+import org.springframework.beans.factory.aot.BeanRegistrationCode;
+import org.springframework.beans.factory.support.RegisteredBean;
+import org.springframework.core.annotation.MergedAnnotation;
+import org.springframework.core.annotation.MergedAnnotations;
+import org.springframework.lang.Nullable;
+import org.springframework.util.ReflectionUtils;
+
+/**
+ * AOT {@code BeanRegistrationAotProcessor} that detects the presence of
+ * {@link Reflective @Reflective} on annotated elements and invoke the
+ * underlying {@link ReflectiveProcessor} implementations.
+ *
+ * @author Stephane Nicoll
+ */
+class ReflectiveProcessorBeanRegistrationAotProcessor implements BeanRegistrationAotProcessor {
+
+	private final Map<Class<? extends ReflectiveProcessor>, ReflectiveProcessor> processors = new HashMap<>();
+
+	@Nullable
+	@Override
+	public BeanRegistrationAotContribution processAheadOfTime(RegisteredBean registeredBean) {
+		Class<?> beanClass = registeredBean.getBeanClass();
+		Set<Entry> entries = new LinkedHashSet<>();
+		if (isReflective(beanClass)) {
+			entries.add(createEntry(beanClass));
+		}
+		doWithReflectiveConstructors(beanClass, constructor ->
+				entries.add(createEntry(constructor)));
+		ReflectionUtils.doWithFields(beanClass, field ->
+				entries.add(createEntry(field)), this::isReflective);
+		ReflectionUtils.doWithMethods(beanClass, method ->
+				entries.add(createEntry(method)), this::isReflective);
+		if (!entries.isEmpty()) {
+			return new ReflectiveProcessorBeanRegistrationAotContribution(entries);
+		}
+		return null;
+	}
+
+	private void doWithReflectiveConstructors(Class<?> beanClass, Consumer<Constructor<?>> consumer) {
+		for (Constructor<?> constructor : beanClass.getDeclaredConstructors()) {
+			if (isReflective(constructor)) {
+				consumer.accept(constructor);
+			}
+		}
+	}
+
+	private boolean isReflective(AnnotatedElement element) {
+		return MergedAnnotations.from(element).isPresent(Reflective.class);
+	}
+
+	@SuppressWarnings("unchecked")
+	private Entry createEntry(AnnotatedElement element) {
+		Class<? extends ReflectiveProcessor>[] processorClasses = (Class<? extends ReflectiveProcessor>[])
+				MergedAnnotations.from(element).get(Reflective.class).getClassArray("value");
+		List<ReflectiveProcessor> processors = Arrays.stream(processorClasses).distinct()
+				.map(processorClass -> this.processors.computeIfAbsent(processorClass, BeanUtils::instantiateClass))
+				.toList();
+		ReflectiveProcessor processorToUse = (processors.size() == 1 ? processors.get(0)
+				: new DelegateReflectiveProcessor(processors));
+		return new Entry(element, processorToUse);
+	}
+
+	static class DelegateReflectiveProcessor implements ReflectiveProcessor {
+
+		private final Iterable<ReflectiveProcessor> processors;
+
+		public DelegateReflectiveProcessor(Iterable<ReflectiveProcessor> processors) {
+			this.processors = processors;
+		}
+
+		@Override
+		public void registerReflectionHints(ReflectionHints hints, AnnotatedElement element) {
+			this.processors.forEach(processor -> processor.registerReflectionHints(hints, element));
+		}
+
+	}
+
+	private record Entry(AnnotatedElement element, ReflectiveProcessor processor) {}
+
+	private static class ReflectiveProcessorBeanRegistrationAotContribution implements BeanRegistrationAotContribution {
+
+		private static final Consumer<Builder> ANNOTATION_CUSTOMIZATIONS = hint -> hint.withMembers(MemberCategory.INVOKE_PUBLIC_METHODS);
+
+		private final Iterable<Entry> entries;
+
+		public ReflectiveProcessorBeanRegistrationAotContribution(Iterable<Entry> entries) {
+			this.entries = entries;
+		}
+
+		@Override
+		public void applyTo(GenerationContext generationContext, BeanRegistrationCode beanRegistrationCode) {
+			RuntimeHints runtimeHints = generationContext.getRuntimeHints();
+			runtimeHints.reflection().registerType(Reflective.class, ANNOTATION_CUSTOMIZATIONS);
+			this.entries.forEach(entry -> {
+				AnnotatedElement element = entry.element();
+				entry.processor().registerReflectionHints(runtimeHints.reflection(), element);
+				registerAnnotationIfNecessary(runtimeHints, element);
+			});
+		}
+
+		private void registerAnnotationIfNecessary(RuntimeHints hints, AnnotatedElement element) {
+			MergedAnnotation<Reflective> reflectiveAnnotation = MergedAnnotations.from(element).get(Reflective.class);
+			if (reflectiveAnnotation.getDistance() > 0) {
+				RuntimeHintsUtils.registerAnnotation(hints, reflectiveAnnotation.getRoot());
+			}
+		}
+
+	}
+
+}