/*
 * Copyright 2002-2019 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.core.annotation;

import java.lang.annotation.Annotation;
import java.lang.reflect.AnnotatedElement;
import java.lang.reflect.Array;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Collection;
import java.util.Collections;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;

import org.springframework.core.BridgeMethodResolver;
import org.springframework.core.annotation.AnnotationTypeMapping.MirrorSets.MirrorSet;
import org.springframework.core.annotation.MergedAnnotation.Adapt;
import org.springframework.core.annotation.MergedAnnotations.SearchStrategy;
import org.springframework.lang.Nullable;
import org.springframework.util.ConcurrentReferenceHashMap;
import org.springframework.util.ReflectionUtils;
import org.springframework.util.StringUtils;

/**
 * General utility methods for working with annotations, handling meta-annotations,
 * bridge methods (which the compiler generates for generic declarations) as well
 * as super methods (for optional <em>annotation inheritance</em>).
 *
 * <p>Note that most of the features of this class are not provided by the
 * JDK's introspection facilities themselves.
 *
 * <p>As a general rule for runtime-retained application annotations (e.g. for
 * transaction control, authorization, or service exposure), always use the
 * lookup methods on this class (e.g. {@link #findAnnotation(Method, Class)} or
 * {@link #getAnnotation(Method, Class)}) instead of the plain annotation lookup
 * methods in the JDK. You can still explicitly choose between a <em>get</em>
 * lookup on the given class level only ({@link #getAnnotation(Method, Class)})
 * and a <em>find</em> lookup in the entire inheritance hierarchy of the given
 * method ({@link #findAnnotation(Method, Class)}).
 *
 * <h3>Terminology</h3>
 * The terms <em>directly present</em>, <em>indirectly present</em>, and
 * <em>present</em> have the same meanings as defined in the class-level
 * javadoc for {@link AnnotatedElement} (in Java 8).
 *
 * <p>An annotation is <em>meta-present</em> on an element if the annotation
 * is declared as a meta-annotation on some other annotation which is
 * <em>present</em> on the element. Annotation {@code A} is <em>meta-present</em>
 * on another annotation if {@code A} is either <em>directly present</em> or
 * <em>meta-present</em> on the other annotation.
 *
 * <h3>Meta-annotation Support</h3>
 * <p>Most {@code find*()} methods and some {@code get*()} methods in this class
 * provide support for finding annotations used as meta-annotations. Consult the
 * javadoc for each method in this class for details. For fine-grained support for
 * meta-annotations with <em>attribute overrides</em> in <em>composed annotations</em>,
 * consider using {@link AnnotatedElementUtils}'s more specific methods instead.
 *
 * <h3>Attribute Aliases</h3>
 * <p>All public methods in this class that return annotations, arrays of
 * annotations, or {@link AnnotationAttributes} transparently support attribute
 * aliases configured via {@link AliasFor @AliasFor}. Consult the various
 * {@code synthesizeAnnotation*(..)} methods for details.
 *
 * <h3>Search Scope</h3>
 * <p>The search algorithms used by methods in this class stop searching for
 * an annotation once the first annotation of the specified type has been
 * found. As a consequence, additional annotations of the specified type will
 * be silently ignored.
 *
 * @author Rob Harrop
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @author Mark Fisher
 * @author Chris Beams
 * @author Phillip Webb
 * @author Oleg Zhurakousky
 * @since 2.0
 * @see AliasFor
 * @see AnnotationAttributes
 * @see AnnotatedElementUtils
 * @see BridgeMethodResolver
 * @see java.lang.reflect.AnnotatedElement#getAnnotations()
 * @see java.lang.reflect.AnnotatedElement#getAnnotation(Class)
 * @see java.lang.reflect.AnnotatedElement#getDeclaredAnnotations()
 */
public abstract class AnnotationUtils {

	/**
	 * The attribute name for annotations with a single element.
	 */
	public static final String VALUE = MergedAnnotation.VALUE;

	private static final AnnotationFilter JAVA_LANG_ANNOTATION_FILTER =
			AnnotationFilter.packages("java.lang.annotation");

	private static final Map<Class<? extends Annotation>, Map<String, DefaultValueHolder>> defaultValuesCache =
			new ConcurrentReferenceHashMap<>();


	/**
	 * Determine whether the given class is a candidate for carrying one of the specified
	 * annotations (at type, method or field level).
	 * @param clazz the class to introspect
	 * @param annotationTypes the searchable annotation types
	 * @return {@code false} if the class is known to have no such annotations at any level;
	 * {@code true} otherwise. Callers will usually perform full method/field introspection
	 * if {@code true} is being returned here.
	 * @since 5.2
	 * @see #isCandidateClass(Class, Class)
	 * @see #isCandidateClass(Class, String)
	 */
	public static boolean isCandidateClass(Class<?> clazz, Collection<Class<? extends Annotation>> annotationTypes) {
		for (Class<? extends Annotation> annotationType : annotationTypes) {
			if (isCandidateClass(clazz, annotationType)) {
				return true;
			}
		}
		return false;
	}

	/**
	 * Determine whether the given class is a candidate for carrying the specified annotation
	 * (at type, method or field level).
	 * @param clazz the class to introspect
	 * @param annotationType the searchable annotation type
	 * @return {@code false} if the class is known to have no such annotations at any level;
	 * {@code true} otherwise. Callers will usually perform full method/field introspection
	 * if {@code true} is being returned here.
	 * @since 5.2
	 * @see #isCandidateClass(Class, String)
	 */
	public static boolean isCandidateClass(Class<?> clazz, Class<? extends Annotation> annotationType) {
		return isCandidateClass(clazz, annotationType.getName());
	}

	/**
	 * Determine whether the given class is a candidate for carrying the specified annotation
	 * (at type, method or field level).
	 * @param clazz the class to introspect
	 * @param annotationName the fully-qualified name of the searchable annotation type
	 * @return {@code false} if the class is known to have no such annotations at any level;
	 * {@code true} otherwise. Callers will usually perform full method/field introspection
	 * if {@code true} is being returned here.
	 * @since 5.2
	 * @see #isCandidateClass(Class, Class)
	 */
	public static boolean isCandidateClass(Class<?> clazz, String annotationName) {
		if (annotationName.startsWith("java.")) {
			return true;
		}
		if (AnnotationsScanner.hasPlainJavaAnnotationsOnly(clazz)) {
			return false;
		}
		return true;
	}

	/**
	 * Get a single {@link Annotation} of {@code annotationType} from the supplied
	 * annotation: either the given annotation itself or a direct meta-annotation
	 * thereof.
	 * <p>Note that this method supports only a single level of meta-annotations.
	 * For support for arbitrary levels of meta-annotations, use one of the
	 * {@code find*()} methods instead.
	 * @param annotation the Annotation to check
	 * @param annotationType the annotation type to look for, both locally and as a meta-annotation
	 * @return the first matching annotation, or {@code null} if not found
	 * @since 4.0
	 */
	@SuppressWarnings("unchecked")
	@Nullable
	public static <A extends Annotation> A getAnnotation(Annotation annotation, Class<A> annotationType) {
		// Shortcut: directly present on the element, with no merging needed?
		if (annotationType.isInstance(annotation)) {
			return synthesizeAnnotation((A) annotation, annotationType);
		}
		// Shortcut: no searchable annotations to be found on plain Java classes and core Spring types...
		if (AnnotationsScanner.hasPlainJavaAnnotationsOnly(annotation)) {
			return null;
		}
		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(annotation, new Annotation[] {annotation}, RepeatableContainers.none())
				.get(annotationType).withNonMergedAttributes()
				.synthesize(AnnotationUtils::isSingleLevelPresent).orElse(null);
	}

	/**
	 * Get a single {@link Annotation} of {@code annotationType} from the supplied
	 * {@link AnnotatedElement}, where the annotation is either <em>present</em> or
	 * <em>meta-present</em> on the {@code AnnotatedElement}.
	 * <p>Note that this method supports only a single level of meta-annotations.
	 * For support for arbitrary levels of meta-annotations, use
	 * {@link #findAnnotation(AnnotatedElement, Class)} instead.
	 * @param annotatedElement the {@code AnnotatedElement} from which to get the annotation
	 * @param annotationType the annotation type to look for, both locally and as a meta-annotation
	 * @return the first matching annotation, or {@code null} if not found
	 * @since 3.1
	 */
	@Nullable
	public static <A extends Annotation> A getAnnotation(AnnotatedElement annotatedElement, Class<A> annotationType) {
		// Shortcut: directly present on the element, with no merging needed?
		if (AnnotationFilter.PLAIN.matches(annotationType) ||
				AnnotationsScanner.hasPlainJavaAnnotationsOnly(annotatedElement)) {
			return annotatedElement.getAnnotation(annotationType);
		}
		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(annotatedElement, SearchStrategy.INHERITED_ANNOTATIONS, RepeatableContainers.none())
				.get(annotationType).withNonMergedAttributes()
				.synthesize(AnnotationUtils::isSingleLevelPresent).orElse(null);
	}

	private static <A extends Annotation> boolean isSingleLevelPresent(MergedAnnotation<A> mergedAnnotation) {
		int distance = mergedAnnotation.getDistance();
		return (distance == 0 || distance == 1);
	}

	/**
	 * Get a single {@link Annotation} of {@code annotationType} from the
	 * supplied {@link Method}, where the annotation is either <em>present</em>
	 * or <em>meta-present</em> on the method.
	 * <p>Correctly handles bridge {@link Method Methods} generated by the compiler.
	 * <p>Note that this method supports only a single level of meta-annotations.
	 * For support for arbitrary levels of meta-annotations, use
	 * {@link #findAnnotation(Method, Class)} instead.
	 * @param method the method to look for annotations on
	 * @param annotationType the annotation type to look for
	 * @return the first matching annotation, or {@code null} if not found
	 * @see org.springframework.core.BridgeMethodResolver#findBridgedMethod(Method)
	 * @see #getAnnotation(AnnotatedElement, Class)
	 */
	@Nullable
	public static <A extends Annotation> A getAnnotation(Method method, Class<A> annotationType) {
		Method resolvedMethod = BridgeMethodResolver.findBridgedMethod(method);
		return getAnnotation((AnnotatedElement) resolvedMethod, annotationType);
	}

	/**
	 * Get all {@link Annotation Annotations} that are <em>present</em> on the
	 * supplied {@link AnnotatedElement}.
	 * <p>Meta-annotations will <em>not</em> be searched.
	 * @param annotatedElement the Method, Constructor or Field to retrieve annotations from
	 * @return the annotations found, an empty array, or {@code null} if not
	 * resolvable (e.g. because nested Class values in annotation attributes
	 * failed to resolve at runtime)
	 * @since 4.0.8
	 * @see AnnotatedElement#getAnnotations()
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	@Nullable
	public static Annotation[] getAnnotations(AnnotatedElement annotatedElement) {
		try {
			return synthesizeAnnotationArray(annotatedElement.getAnnotations(), annotatedElement);
		}
		catch (Throwable ex) {
			handleIntrospectionFailure(annotatedElement, ex);
			return null;
		}
	}

	/**
	 * Get all {@link Annotation Annotations} that are <em>present</em> on the
	 * supplied {@link Method}.
	 * <p>Correctly handles bridge {@link Method Methods} generated by the compiler.
	 * <p>Meta-annotations will <em>not</em> be searched.
	 * @param method the Method to retrieve annotations from
	 * @return the annotations found, an empty array, or {@code null} if not
	 * resolvable (e.g. because nested Class values in annotation attributes
	 * failed to resolve at runtime)
	 * @see org.springframework.core.BridgeMethodResolver#findBridgedMethod(Method)
	 * @see AnnotatedElement#getAnnotations()
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	@Nullable
	public static Annotation[] getAnnotations(Method method) {
		try {
			return synthesizeAnnotationArray(BridgeMethodResolver.findBridgedMethod(method).getAnnotations(), method);
		}
		catch (Throwable ex) {
			handleIntrospectionFailure(method, ex);
			return null;
		}
	}

	/**
	 * Get the <em>repeatable</em> {@linkplain Annotation annotations} of
	 * {@code annotationType} from the supplied {@link AnnotatedElement}, where
	 * such annotations are either <em>present</em>, <em>indirectly present</em>,
	 * or <em>meta-present</em> on the element.
	 * <p>This method mimics the functionality of Java 8's
	 * {@link java.lang.reflect.AnnotatedElement#getAnnotationsByType(Class)}
	 * with support for automatic detection of a <em>container annotation</em>
	 * declared via @{@link java.lang.annotation.Repeatable} (when running on
	 * Java 8 or higher) and with additional support for meta-annotations.
	 * <p>Handles both single annotations and annotations nested within a
	 * <em>container annotation</em>.
	 * <p>Correctly handles <em>bridge methods</em> generated by the
	 * compiler if the supplied element is a {@link Method}.
	 * <p>Meta-annotations will be searched if the annotation is not
	 * <em>present</em> on the supplied element.
	 * @param annotatedElement the element to look for annotations on
	 * @param annotationType the annotation type to look for
	 * @return the annotations found or an empty set (never {@code null})
	 * @since 4.2
	 * @see #getRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class)
	 * @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
	 * @see java.lang.annotation.Repeatable
	 * @see java.lang.reflect.AnnotatedElement#getAnnotationsByType
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	public static <A extends Annotation> Set<A> getRepeatableAnnotations(AnnotatedElement annotatedElement,
			Class<A> annotationType) {

		return getRepeatableAnnotations(annotatedElement, annotationType, null);
	}

	/**
	 * Get the <em>repeatable</em> {@linkplain Annotation annotations} of
	 * {@code annotationType} from the supplied {@link AnnotatedElement}, where
	 * such annotations are either <em>present</em>, <em>indirectly present</em>,
	 * or <em>meta-present</em> on the element.
	 * <p>This method mimics the functionality of Java 8's
	 * {@link java.lang.reflect.AnnotatedElement#getAnnotationsByType(Class)}
	 * with additional support for meta-annotations.
	 * <p>Handles both single annotations and annotations nested within a
	 * <em>container annotation</em>.
	 * <p>Correctly handles <em>bridge methods</em> generated by the
	 * compiler if the supplied element is a {@link Method}.
	 * <p>Meta-annotations will be searched if the annotation is not
	 * <em>present</em> on the supplied element.
	 * @param annotatedElement the element to look for annotations on
	 * @param annotationType the annotation type to look for
	 * @param containerAnnotationType the type of the container that holds
	 * the annotations; may be {@code null} if a container is not supported
	 * or if it should be looked up via @{@link java.lang.annotation.Repeatable}
	 * when running on Java 8 or higher
	 * @return the annotations found or an empty set (never {@code null})
	 * @since 4.2
	 * @see #getRepeatableAnnotations(AnnotatedElement, Class)
	 * @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class)
	 * @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
	 * @see java.lang.annotation.Repeatable
	 * @see java.lang.reflect.AnnotatedElement#getAnnotationsByType
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	public static <A extends Annotation> Set<A> getRepeatableAnnotations(AnnotatedElement annotatedElement,
			Class<A> annotationType, @Nullable Class<? extends Annotation> containerAnnotationType) {

		RepeatableContainers repeatableContainers = (containerAnnotationType != null ?
				RepeatableContainers.of(annotationType, containerAnnotationType) :
				RepeatableContainers.standardRepeatables());

		return MergedAnnotations.from(annotatedElement, SearchStrategy.SUPERCLASS, repeatableContainers)
				.stream(annotationType)
				.filter(MergedAnnotationPredicates.firstRunOf(MergedAnnotation::getAggregateIndex))
				.map(MergedAnnotation::withNonMergedAttributes)
				.collect(MergedAnnotationCollectors.toAnnotationSet());
	}

	/**
	 * Get the declared <em>repeatable</em> {@linkplain Annotation annotations}
	 * of {@code annotationType} from the supplied {@link AnnotatedElement},
	 * where such annotations are either <em>directly present</em>,
	 * <em>indirectly present</em>, or <em>meta-present</em> on the element.
	 * <p>This method mimics the functionality of Java 8's
	 * {@link java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType(Class)}
	 * with support for automatic detection of a <em>container annotation</em>
	 * declared via @{@link java.lang.annotation.Repeatable} (when running on
	 * Java 8 or higher) and with additional support for meta-annotations.
	 * <p>Handles both single annotations and annotations nested within a
	 * <em>container annotation</em>.
	 * <p>Correctly handles <em>bridge methods</em> generated by the
	 * compiler if the supplied element is a {@link Method}.
	 * <p>Meta-annotations will be searched if the annotation is not
	 * <em>present</em> on the supplied element.
	 * @param annotatedElement the element to look for annotations on
	 * @param annotationType the annotation type to look for
	 * @return the annotations found or an empty set (never {@code null})
	 * @since 4.2
	 * @see #getRepeatableAnnotations(AnnotatedElement, Class)
	 * @see #getRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class)
	 * @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
	 * @see java.lang.annotation.Repeatable
	 * @see java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	public static <A extends Annotation> Set<A> getDeclaredRepeatableAnnotations(AnnotatedElement annotatedElement,
			Class<A> annotationType) {

		return getDeclaredRepeatableAnnotations(annotatedElement, annotationType, null);
	}

	/**
	 * Get the declared <em>repeatable</em> {@linkplain Annotation annotations}
	 * of {@code annotationType} from the supplied {@link AnnotatedElement},
	 * where such annotations are either <em>directly present</em>,
	 * <em>indirectly present</em>, or <em>meta-present</em> on the element.
	 * <p>This method mimics the functionality of Java 8's
	 * {@link java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType(Class)}
	 * with additional support for meta-annotations.
	 * <p>Handles both single annotations and annotations nested within a
	 * <em>container annotation</em>.
	 * <p>Correctly handles <em>bridge methods</em> generated by the
	 * compiler if the supplied element is a {@link Method}.
	 * <p>Meta-annotations will be searched if the annotation is not
	 * <em>present</em> on the supplied element.
	 * @param annotatedElement the element to look for annotations on
	 * @param annotationType the annotation type to look for
	 * @param containerAnnotationType the type of the container that holds
	 * the annotations; may be {@code null} if a container is not supported
	 * or if it should be looked up via @{@link java.lang.annotation.Repeatable}
	 * when running on Java 8 or higher
	 * @return the annotations found or an empty set (never {@code null})
	 * @since 4.2
	 * @see #getRepeatableAnnotations(AnnotatedElement, Class)
	 * @see #getRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class)
	 * @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class, Class)
	 * @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
	 * @see java.lang.annotation.Repeatable
	 * @see java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	public static <A extends Annotation> Set<A> getDeclaredRepeatableAnnotations(AnnotatedElement annotatedElement,
			Class<A> annotationType, @Nullable Class<? extends Annotation> containerAnnotationType) {

		RepeatableContainers repeatableContainers = containerAnnotationType != null ?
				RepeatableContainers.of(annotationType, containerAnnotationType) :
				RepeatableContainers.standardRepeatables();

		return MergedAnnotations.from(annotatedElement, SearchStrategy.DIRECT, repeatableContainers)
				.stream(annotationType)
				.map(MergedAnnotation::withNonMergedAttributes)
				.collect(MergedAnnotationCollectors.toAnnotationSet());
	}

	/**
	 * Find a single {@link Annotation} of {@code annotationType} on the
	 * supplied {@link AnnotatedElement}.
	 * <p>Meta-annotations will be searched if the annotation is not
	 * <em>directly present</em> on the supplied element.
	 * <p><strong>Warning</strong>: this method operates generically on
	 * annotated elements. In other words, this method does not execute
	 * specialized search algorithms for classes or methods. If you require
	 * the more specific semantics of {@link #findAnnotation(Class, Class)}
	 * or {@link #findAnnotation(Method, Class)}, invoke one of those methods
	 * instead.
	 * @param annotatedElement the {@code AnnotatedElement} on which to find the annotation
	 * @param annotationType the annotation type to look for, both locally and as a meta-annotation
	 * @return the first matching annotation, or {@code null} if not found
	 * @since 4.2
	 */
	@Nullable
	public static <A extends Annotation> A findAnnotation(
			AnnotatedElement annotatedElement, @Nullable Class<A> annotationType) {

		if (annotationType == null) {
			return null;
		}

		// Shortcut: directly present on the element, with no merging needed?
		if (AnnotationFilter.PLAIN.matches(annotationType) ||
				AnnotationsScanner.hasPlainJavaAnnotationsOnly(annotatedElement)) {
			return annotatedElement.getDeclaredAnnotation(annotationType);
		}

		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(annotatedElement, SearchStrategy.INHERITED_ANNOTATIONS, RepeatableContainers.none())
				.get(annotationType).withNonMergedAttributes()
				.synthesize(MergedAnnotation::isPresent).orElse(null);
	}

	/**
	 * Find a single {@link Annotation} of {@code annotationType} on the supplied
	 * {@link Method}, traversing its super methods (i.e. from superclasses and
	 * interfaces) if the annotation is not <em>directly present</em> on the given
	 * method itself.
	 * <p>Correctly handles bridge {@link Method Methods} generated by the compiler.
	 * <p>Meta-annotations will be searched if the annotation is not
	 * <em>directly present</em> on the method.
	 * <p>Annotations on methods are not inherited by default, so we need to handle
	 * this explicitly.
	 * @param method the method to look for annotations on
	 * @param annotationType the annotation type to look for
	 * @return the first matching annotation, or {@code null} if not found
	 * @see #getAnnotation(Method, Class)
	 */
	@Nullable
	public static <A extends Annotation> A findAnnotation(Method method, @Nullable Class<A> annotationType) {
		if (annotationType == null) {
			return null;
		}

		// Shortcut: directly present on the element, with no merging needed?
		if (AnnotationFilter.PLAIN.matches(annotationType) ||
				AnnotationsScanner.hasPlainJavaAnnotationsOnly(method)) {
			return method.getDeclaredAnnotation(annotationType);
		}

		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(method, SearchStrategy.TYPE_HIERARCHY, RepeatableContainers.none())
				.get(annotationType).withNonMergedAttributes()
				.synthesize(MergedAnnotation::isPresent).orElse(null);
	}

	/**
	 * Find a single {@link Annotation} of {@code annotationType} on the
	 * supplied {@link Class}, traversing its interfaces, annotations, and
	 * superclasses if the annotation is not <em>directly present</em> on
	 * the given class itself.
	 * <p>This method explicitly handles class-level annotations which are not
	 * declared as {@link java.lang.annotation.Inherited inherited} <em>as well
	 * as meta-annotations and annotations on interfaces</em>.
	 * <p>The algorithm operates as follows:
	 * <ol>
	 * <li>Search for the annotation on the given class and return it if found.
	 * <li>Recursively search through all annotations that the given class declares.
	 * <li>Recursively search through all interfaces that the given class declares.
	 * <li>Recursively search through the superclass hierarchy of the given class.
	 * </ol>
	 * <p>Note: in this context, the term <em>recursively</em> means that the search
	 * process continues by returning to step #1 with the current interface,
	 * annotation, or superclass as the class to look for annotations on.
	 * @param clazz the class to look for annotations on
	 * @param annotationType the type of annotation to look for
	 * @return the first matching annotation, or {@code null} if not found
	 */
	@Nullable
	public static <A extends Annotation> A findAnnotation(Class<?> clazz, @Nullable Class<A> annotationType) {
		if (annotationType == null) {
			return null;
		}

		// Shortcut: directly present on the element, with no merging needed?
		if (AnnotationFilter.PLAIN.matches(annotationType) ||
				AnnotationsScanner.hasPlainJavaAnnotationsOnly(clazz)) {
			A annotation = clazz.getDeclaredAnnotation(annotationType);
			if (annotation != null) {
				return annotation;
			}
			// For backwards compatibility, perform a superclass search with plain annotations
			// even if not marked as @Inherited: e.g. a findAnnotation search for @Deprecated
			Class<?> superclass = clazz.getSuperclass();
			if (superclass == null || superclass == Object.class) {
				return null;
			}
			return findAnnotation(superclass, annotationType);
		}

		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(clazz, SearchStrategy.TYPE_HIERARCHY, RepeatableContainers.none())
				.get(annotationType).withNonMergedAttributes()
				.synthesize(MergedAnnotation::isPresent).orElse(null);
	}

	/**
	 * Find the first {@link Class} in the inheritance hierarchy of the
	 * specified {@code clazz} (including the specified {@code clazz} itself)
	 * on which an annotation of the specified {@code annotationType} is
	 * <em>directly present</em>.
	 * <p>If the supplied {@code clazz} is an interface, only the interface
	 * itself will be checked; the inheritance hierarchy for interfaces will
	 * not be traversed.
	 * <p>Meta-annotations will <em>not</em> be searched.
	 * <p>The standard {@link Class} API does not provide a mechanism for
	 * determining which class in an inheritance hierarchy actually declares
	 * an {@link Annotation}, so we need to handle this explicitly.
	 * @param annotationType the annotation type to look for
	 * @param clazz the class to check for the annotation on (may be {@code null})
	 * @return the first {@link Class} in the inheritance hierarchy that
	 * declares an annotation of the specified {@code annotationType},
	 * or {@code null} if not found
	 * @see Class#isAnnotationPresent(Class)
	 * @see Class#getDeclaredAnnotations()
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	@Nullable
	public static Class<?> findAnnotationDeclaringClass(
			Class<? extends Annotation> annotationType, @Nullable Class<?> clazz) {

		if (clazz == null) {
			return null;
		}

		return (Class<?>) MergedAnnotations.from(clazz, SearchStrategy.SUPERCLASS)
				.get(annotationType, MergedAnnotation::isDirectlyPresent)
				.getSource();
	}

	/**
	 * Find the first {@link Class} in the inheritance hierarchy of the
	 * specified {@code clazz} (including the specified {@code clazz} itself)
	 * on which at least one of the specified {@code annotationTypes} is
	 * <em>directly present</em>.
	 * <p>If the supplied {@code clazz} is an interface, only the interface
	 * itself will be checked; the inheritance hierarchy for interfaces will
	 * not be traversed.
	 * <p>Meta-annotations will <em>not</em> be searched.
	 * <p>The standard {@link Class} API does not provide a mechanism for
	 * determining which class in an inheritance hierarchy actually declares
	 * one of several candidate {@linkplain Annotation annotations}, so we
	 * need to handle this explicitly.
	 * @param annotationTypes the annotation types to look for
	 * @param clazz the class to check for the annotation on (may be {@code null})
	 * @return the first {@link Class} in the inheritance hierarchy that
	 * declares an annotation of at least one of the specified
	 * {@code annotationTypes}, or {@code null} if not found
	 * @since 3.2.2
	 * @see Class#isAnnotationPresent(Class)
	 * @see Class#getDeclaredAnnotations()
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	@Nullable
	public static Class<?> findAnnotationDeclaringClassForTypes(
			List<Class<? extends Annotation>> annotationTypes, @Nullable Class<?> clazz) {

		if (clazz == null) {
			return null;
		}

		return (Class<?>) MergedAnnotations.from(clazz, SearchStrategy.SUPERCLASS)
				.stream()
				.filter(MergedAnnotationPredicates.typeIn(annotationTypes).and(MergedAnnotation::isDirectlyPresent))
				.map(MergedAnnotation::getSource)
				.findFirst().orElse(null);
	}

	/**
	 * Determine whether an annotation of the specified {@code annotationType}
	 * is declared locally (i.e. <em>directly present</em>) on the supplied
	 * {@code clazz}.
	 * <p>The supplied {@link Class} may represent any type.
	 * <p>Meta-annotations will <em>not</em> be searched.
	 * <p>Note: This method does <strong>not</strong> determine if the annotation
	 * is {@linkplain java.lang.annotation.Inherited inherited}.
	 * @param annotationType the annotation type to look for
	 * @param clazz the class to check for the annotation on
	 * @return {@code true} if an annotation of the specified {@code annotationType}
	 * is <em>directly present</em>
	 * @see java.lang.Class#getDeclaredAnnotations()
	 * @see java.lang.Class#getDeclaredAnnotation(Class)
	 */
	public static boolean isAnnotationDeclaredLocally(Class<? extends Annotation> annotationType, Class<?> clazz) {
		return MergedAnnotations.from(clazz).get(annotationType).isDirectlyPresent();
	}

	/**
	 * Determine whether an annotation of the specified {@code annotationType}
	 * is <em>present</em> on the supplied {@code clazz} and is
	 * {@linkplain java.lang.annotation.Inherited inherited}
	 * (i.e. not <em>directly present</em>).
	 * <p>Meta-annotations will <em>not</em> be searched.
	 * <p>If the supplied {@code clazz} is an interface, only the interface
	 * itself will be checked. In accordance with standard meta-annotation
	 * semantics in Java, the inheritance hierarchy for interfaces will not
	 * be traversed. See the {@linkplain java.lang.annotation.Inherited javadoc}
	 * for the {@code @Inherited} meta-annotation for further details regarding
	 * annotation inheritance.
	 * @param annotationType the annotation type to look for
	 * @param clazz the class to check for the annotation on
	 * @return {@code true} if an annotation of the specified {@code annotationType}
	 * is <em>present</em> and <em>inherited</em>
	 * @see Class#isAnnotationPresent(Class)
	 * @see #isAnnotationDeclaredLocally(Class, Class)
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	public static boolean isAnnotationInherited(Class<? extends Annotation> annotationType, Class<?> clazz) {
		return MergedAnnotations.from(clazz, SearchStrategy.INHERITED_ANNOTATIONS)
				.stream(annotationType)
				.filter(MergedAnnotation::isDirectlyPresent)
				.findFirst().orElseGet(MergedAnnotation::missing)
				.getAggregateIndex() > 0;
	}

	/**
	 * Determine if an annotation of type {@code metaAnnotationType} is
	 * <em>meta-present</em> on the supplied {@code annotationType}.
	 * @param annotationType the annotation type to search on
	 * @param metaAnnotationType the type of meta-annotation to search for
	 * @return {@code true} if such an annotation is meta-present
	 * @since 4.2.1
	 * @deprecated as of 5.2 since it is superseded by the {@link MergedAnnotations} API
	 */
	@Deprecated
	public static boolean isAnnotationMetaPresent(Class<? extends Annotation> annotationType,
			@Nullable Class<? extends Annotation> metaAnnotationType) {

		if (metaAnnotationType == null) {
			return false;
		}
		// Shortcut: directly present on the element, with no merging needed?
		if (AnnotationFilter.PLAIN.matches(metaAnnotationType) ||
				AnnotationsScanner.hasPlainJavaAnnotationsOnly(annotationType)) {
			return annotationType.isAnnotationPresent(metaAnnotationType);
		}
		// Exhaustive retrieval of merged annotations...
		return MergedAnnotations.from(annotationType, SearchStrategy.INHERITED_ANNOTATIONS,
				RepeatableContainers.none()).isPresent(metaAnnotationType);
	}

	/**
	 * Determine if the supplied {@link Annotation} is defined in the core JDK
	 * {@code java.lang.annotation} package.
	 * @param annotation the annotation to check
	 * @return {@code true} if the annotation is in the {@code java.lang.annotation} package
	 */
	public static boolean isInJavaLangAnnotationPackage(@Nullable Annotation annotation) {
		return (annotation != null && JAVA_LANG_ANNOTATION_FILTER.matches(annotation));
	}

	/**
	 * Determine if the {@link Annotation} with the supplied name is defined
	 * in the core JDK {@code java.lang.annotation} package.
	 * @param annotationType the name of the annotation type to check
	 * @return {@code true} if the annotation is in the {@code java.lang.annotation} package
	 * @since 4.2
	 */
	public static boolean isInJavaLangAnnotationPackage(@Nullable String annotationType) {
		return (annotationType != null && JAVA_LANG_ANNOTATION_FILTER.matches(annotationType));
	}

	/**
	 * Check the declared attributes of the given annotation, in particular covering
	 * Google App Engine's late arrival of {@code TypeNotPresentExceptionProxy} for
	 * {@code Class} values (instead of early {@code Class.getAnnotations() failure}.
	 * <p>This method not failing indicates that {@link #getAnnotationAttributes(Annotation)}
	 * won't failure either (when attempted later on).
	 * @param annotation the annotation to validate
	 * @throws IllegalStateException if a declared {@code Class} attribute could not be read
	 * @since 4.3.15
	 * @see Class#getAnnotations()
	 * @see #getAnnotationAttributes(Annotation)
	 */
	public static void validateAnnotation(Annotation annotation) {
		AttributeMethods.forAnnotationType(annotation.annotationType()).validate(annotation);
	}

	/**
	 * Retrieve the given annotation's attributes as a {@link Map}, preserving all
	 * attribute types.
	 * <p>Equivalent to calling {@link #getAnnotationAttributes(Annotation, boolean, boolean)}
	 * with the {@code classValuesAsString} and {@code nestedAnnotationsAsMap} parameters
	 * set to {@code false}.
	 * <p>Note: This method actually returns an {@link AnnotationAttributes} instance.
	 * However, the {@code Map} signature has been preserved for binary compatibility.
	 * @param annotation the annotation to retrieve the attributes for
	 * @return the Map of annotation attributes, with attribute names as keys and
	 * corresponding attribute values as values (never {@code null})
	 * @see #getAnnotationAttributes(AnnotatedElement, Annotation)
	 * @see #getAnnotationAttributes(Annotation, boolean, boolean)
	 * @see #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)
	 */
	public static Map<String, Object> getAnnotationAttributes(Annotation annotation) {
		return getAnnotationAttributes(null, annotation);
	}

	/**
	 * Retrieve the given annotation's attributes as a {@link Map}.
	 * <p>Equivalent to calling {@link #getAnnotationAttributes(Annotation, boolean, boolean)}
	 * with the {@code nestedAnnotationsAsMap} parameter set to {@code false}.
	 * <p>Note: This method actually returns an {@link AnnotationAttributes} instance.
	 * However, the {@code Map} signature has been preserved for binary compatibility.
	 * @param annotation the annotation to retrieve the attributes for
	 * @param classValuesAsString whether to convert Class references into Strings (for
	 * compatibility with {@link org.springframework.core.type.AnnotationMetadata})
	 * or to preserve them as Class references
	 * @return the Map of annotation attributes, with attribute names as keys and
	 * corresponding attribute values as values (never {@code null})
	 * @see #getAnnotationAttributes(Annotation, boolean, boolean)
	 */
	public static Map<String, Object> getAnnotationAttributes(
			Annotation annotation, boolean classValuesAsString) {

		return getAnnotationAttributes(annotation, classValuesAsString, false);
	}

	/**
	 * Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
	 * <p>This method provides fully recursive annotation reading capabilities on par with
	 * the reflection-based {@link org.springframework.core.type.StandardAnnotationMetadata}.
	 * @param annotation the annotation to retrieve the attributes for
	 * @param classValuesAsString whether to convert Class references into Strings (for
	 * compatibility with {@link org.springframework.core.type.AnnotationMetadata})
	 * or to preserve them as Class references
	 * @param nestedAnnotationsAsMap whether to convert nested annotations into
	 * {@link AnnotationAttributes} maps (for compatibility with
	 * {@link org.springframework.core.type.AnnotationMetadata}) or to preserve them as
	 * {@code Annotation} instances
	 * @return the annotation attributes (a specialized Map) with attribute names as keys
	 * and corresponding attribute values as values (never {@code null})
	 * @since 3.1.1
	 */
	public static AnnotationAttributes getAnnotationAttributes(
			Annotation annotation, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

		return getAnnotationAttributes(null, annotation, classValuesAsString, nestedAnnotationsAsMap);
	}

	/**
	 * Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
	 * <p>Equivalent to calling {@link #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)}
	 * with the {@code classValuesAsString} and {@code nestedAnnotationsAsMap} parameters
	 * set to {@code false}.
	 * @param annotatedElement the element that is annotated with the supplied annotation;
	 * may be {@code null} if unknown
	 * @param annotation the annotation to retrieve the attributes for
	 * @return the annotation attributes (a specialized Map) with attribute names as keys
	 * and corresponding attribute values as values (never {@code null})
	 * @since 4.2
	 * @see #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)
	 */
	public static AnnotationAttributes getAnnotationAttributes(
			@Nullable AnnotatedElement annotatedElement, Annotation annotation) {

		return getAnnotationAttributes(annotatedElement, annotation, false, false);
	}

	/**
	 * Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
	 * <p>This method provides fully recursive annotation reading capabilities on par with
	 * the reflection-based {@link org.springframework.core.type.StandardAnnotationMetadata}.
	 * @param annotatedElement the element that is annotated with the supplied annotation;
	 * may be {@code null} if unknown
	 * @param annotation the annotation to retrieve the attributes for
	 * @param classValuesAsString whether to convert Class references into Strings (for
	 * compatibility with {@link org.springframework.core.type.AnnotationMetadata})
	 * or to preserve them as Class references
	 * @param nestedAnnotationsAsMap whether to convert nested annotations into
	 * {@link AnnotationAttributes} maps (for compatibility with
	 * {@link org.springframework.core.type.AnnotationMetadata}) or to preserve them as
	 * {@code Annotation} instances
	 * @return the annotation attributes (a specialized Map) with attribute names as keys
	 * and corresponding attribute values as values (never {@code null})
	 * @since 4.2
	 */
	public static AnnotationAttributes getAnnotationAttributes(
			@Nullable AnnotatedElement annotatedElement, Annotation annotation,
			boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

		Adapt[] adaptations = Adapt.values(classValuesAsString, nestedAnnotationsAsMap);
		return MergedAnnotation.from(annotatedElement, annotation)
				.withNonMergedAttributes()
				.asMap(mergedAnnotation ->
						new AnnotationAttributes(mergedAnnotation.getType(), true), adaptations);
	}

	/**
	 * Register the annotation-declared default values for the given attributes,
	 * if available.
	 * @param attributes the annotation attributes to process
	 * @since 4.3.2
	 */
	public static void registerDefaultValues(AnnotationAttributes attributes) {
		Class<? extends Annotation> annotationType = attributes.annotationType();
		if (annotationType != null && Modifier.isPublic(annotationType.getModifiers()) &&
				!AnnotationFilter.PLAIN.matches(annotationType)) {
			Map<String, DefaultValueHolder> defaultValues = getDefaultValues(annotationType);
			defaultValues.forEach(attributes::putIfAbsent);
		}
	}

	private static Map<String, DefaultValueHolder> getDefaultValues(
			Class<? extends Annotation> annotationType) {

		return defaultValuesCache.computeIfAbsent(annotationType,
				AnnotationUtils::computeDefaultValues);
	}

	private static Map<String, DefaultValueHolder> computeDefaultValues(
			Class<? extends Annotation> annotationType) {

		AttributeMethods methods = AttributeMethods.forAnnotationType(annotationType);
		if (!methods.hasDefaultValueMethod()) {
			return Collections.emptyMap();
		}
		Map<String, DefaultValueHolder> result = new LinkedHashMap<>(methods.size());
		if (!methods.hasNestedAnnotation()) {
			// Use simpler method if there are no nested annotations
			for (int i = 0; i < methods.size(); i++) {
				Method method = methods.get(i);
				Object defaultValue = method.getDefaultValue();
				if (defaultValue != null) {
					result.put(method.getName(), new DefaultValueHolder(defaultValue));
				}
			}
		}
		else {
			// If we have nested annotations, we need them as nested maps
			AnnotationAttributes attributes = MergedAnnotation.of(annotationType)
					.asMap(annotation ->
							new AnnotationAttributes(annotation.getType(), true), Adapt.ANNOTATION_TO_MAP);
			for (Map.Entry<String, Object> element : attributes.entrySet()) {
				result.put(element.getKey(), new DefaultValueHolder(element.getValue()));
			}
		}
		return result;
	}

	/**
	 * Post-process the supplied {@link AnnotationAttributes}, preserving nested
	 * annotations as {@code Annotation} instances.
	 * <p>Specifically, this method enforces <em>attribute alias</em> semantics
	 * for annotation attributes that are annotated with {@link AliasFor @AliasFor}
	 * and replaces default value placeholders with their original default values.
	 * @param annotatedElement the element that is annotated with an annotation or
	 * annotation hierarchy from which the supplied attributes were created;
	 * may be {@code null} if unknown
	 * @param attributes the annotation attributes to post-process
	 * @param classValuesAsString whether to convert Class references into Strings (for
	 * compatibility with {@link org.springframework.core.type.AnnotationMetadata})
	 * or to preserve them as Class references
	 * @since 4.3.2
	 * @see #getDefaultValue(Class, String)
	 */
	public static void postProcessAnnotationAttributes(@Nullable Object annotatedElement,
			@Nullable AnnotationAttributes attributes, boolean classValuesAsString) {

		if (attributes == null) {
			return;
		}
		if (!attributes.validated) {
			Class<? extends Annotation> annotationType = attributes.annotationType();
			if (annotationType == null) {
				return;
			}
			AnnotationTypeMapping mapping = AnnotationTypeMappings.forAnnotationType(annotationType).get(0);
			for (int i = 0; i < mapping.getMirrorSets().size(); i++) {
				MirrorSet mirrorSet = mapping.getMirrorSets().get(i);
				int resolved = mirrorSet.resolve(attributes.displayName, attributes,
						AnnotationUtils::getAttributeValueForMirrorResolution);
				if (resolved != -1) {
					Method attribute = mapping.getAttributes().get(resolved);
					Object value = attributes.get(attribute.getName());
					for (int j = 0; j < mirrorSet.size(); j++) {
						Method mirror = mirrorSet.get(j);
						if (mirror != attribute) {
							attributes.put(mirror.getName(),
									adaptValue(annotatedElement, value, classValuesAsString));
						}
					}
				}
			}
		}
		for (Map.Entry<String, Object> attributeEntry : attributes.entrySet()) {
			String attributeName = attributeEntry.getKey();
			Object value = attributeEntry.getValue();
			if (value instanceof DefaultValueHolder) {
				value = ((DefaultValueHolder) value).defaultValue;
				attributes.put(attributeName,
						adaptValue(annotatedElement, value, classValuesAsString));
			}
		}
	}

	private static Object getAttributeValueForMirrorResolution(Method attribute, Object attributes) {
		Object result = ((AnnotationAttributes) attributes).get(attribute.getName());
		return (result instanceof DefaultValueHolder ? ((DefaultValueHolder) result).defaultValue : result);
	}

	@Nullable
	private static Object adaptValue(
			@Nullable Object annotatedElement, @Nullable Object value, boolean classValuesAsString) {

		if (classValuesAsString) {
			if (value instanceof Class) {
				return ((Class<?>) value).getName();
			}
			if (value instanceof Class[]) {
				Class<?>[] classes = (Class<?>[]) value;
				String[] names = new String[classes.length];
				for (int i = 0; i < classes.length; i++) {
					names[i] = classes[i].getName();
				}
				return names;
			}
		}
		if (value instanceof Annotation) {
			Annotation annotation = (Annotation) value;
			return MergedAnnotation.from(annotatedElement, annotation).synthesize();
		}
		if (value instanceof Annotation[]) {
			Annotation[] annotations = (Annotation[]) value;
			Annotation[] synthesized = (Annotation[]) Array.newInstance(
					annotations.getClass().getComponentType(), annotations.length);
			for (int i = 0; i < annotations.length; i++) {
				synthesized[i] = MergedAnnotation.from(annotatedElement, annotations[i]).synthesize();
			}
			return synthesized;
		}
		return value;
	}

	/**
	 * Retrieve the <em>value</em> of the {@code value} attribute of a
	 * single-element Annotation, given an annotation instance.
	 * @param annotation the annotation instance from which to retrieve the value
	 * @return the attribute value, or {@code null} if not found unless the attribute
	 * value cannot be retrieved due to an {@link AnnotationConfigurationException},
	 * in which case such an exception will be rethrown
	 * @see #getValue(Annotation, String)
	 */
	@Nullable
	public static Object getValue(Annotation annotation) {
		return getValue(annotation, VALUE);
	}

	/**
	 * Retrieve the <em>value</em> of a named attribute, given an annotation instance.
	 * @param annotation the annotation instance from which to retrieve the value
	 * @param attributeName the name of the attribute value to retrieve
	 * @return the attribute value, or {@code null} if not found unless the attribute
	 * value cannot be retrieved due to an {@link AnnotationConfigurationException},
	 * in which case such an exception will be rethrown
	 * @see #getValue(Annotation)
	 */
	@Nullable
	public static Object getValue(@Nullable Annotation annotation, @Nullable String attributeName) {
		if (annotation == null || !StringUtils.hasText(attributeName)) {
			return null;
		}
		try {
			Method method = annotation.annotationType().getDeclaredMethod(attributeName);
			ReflectionUtils.makeAccessible(method);
			return method.invoke(annotation);
		}
		catch (NoSuchMethodException ex) {
			return null;
		}
		catch (InvocationTargetException ex) {
			rethrowAnnotationConfigurationException(ex.getTargetException());
			throw new IllegalStateException("Could not obtain value for annotation attribute '" +
					attributeName + "' in " + annotation, ex);
		}
		catch (Throwable ex) {
			handleIntrospectionFailure(annotation.getClass(), ex);
			return null;
		}
	}

	/**
	 * If the supplied throwable is an {@link AnnotationConfigurationException},
	 * it will be cast to an {@code AnnotationConfigurationException} and thrown,
	 * allowing it to propagate to the caller.
	 * <p>Otherwise, this method does nothing.
	 * @param ex the throwable to inspect
	 */
	private static void rethrowAnnotationConfigurationException(Throwable ex) {
		if (ex instanceof AnnotationConfigurationException) {
			throw (AnnotationConfigurationException) ex;
		}
	}

	/**
	 * Handle the supplied annotation introspection exception.
	 * <p>If the supplied exception is an {@link AnnotationConfigurationException},
	 * it will simply be thrown, allowing it to propagate to the caller, and
	 * nothing will be logged.
	 * <p>Otherwise, this method logs an introspection failure (in particular
	 * {@code TypeNotPresentExceptions}) before moving on, assuming nested
	 * Class values were not resolvable within annotation attributes and
	 * thereby effectively pretending there were no annotations on the specified
	 * element.
	 * @param element the element that we tried to introspect annotations on
	 * @param ex the exception that we encountered
	 * @see #rethrowAnnotationConfigurationException
	 */
	private static void handleIntrospectionFailure(@Nullable AnnotatedElement element, Throwable ex) {
		rethrowAnnotationConfigurationException(ex);
		IntrospectionFailureLogger logger = IntrospectionFailureLogger.INFO;
		boolean meta = false;
		if (element instanceof Class && Annotation.class.isAssignableFrom((Class<?>) element)) {
			// Meta-annotation or (default) value lookup on an annotation type
			logger = IntrospectionFailureLogger.DEBUG;
			meta = true;
		}
		if (logger.isEnabled()) {
			String message = meta ?
					"Failed to meta-introspect annotation " :
					"Failed to introspect annotations on ";
			logger.log(message + element + ": " + ex);
		}
	}

	/**
	 * Retrieve the <em>default value</em> of the {@code value} attribute
	 * of a single-element Annotation, given an annotation instance.
	 * @param annotation the annotation instance from which to retrieve the default value
	 * @return the default value, or {@code null} if not found
	 * @see #getDefaultValue(Annotation, String)
	 */
	@Nullable
	public static Object getDefaultValue(Annotation annotation) {
		return getDefaultValue(annotation, VALUE);
	}

	/**
	 * Retrieve the <em>default value</em> of a named attribute, given an annotation instance.
	 * @param annotation the annotation instance from which to retrieve the default value
	 * @param attributeName the name of the attribute value to retrieve
	 * @return the default value of the named attribute, or {@code null} if not found
	 * @see #getDefaultValue(Class, String)
	 */
	@Nullable
	public static Object getDefaultValue(@Nullable Annotation annotation, @Nullable String attributeName) {
		return (annotation != null ? getDefaultValue(annotation.annotationType(), attributeName) : null);
	}

	/**
	 * Retrieve the <em>default value</em> of the {@code value} attribute
	 * of a single-element Annotation, given the {@link Class annotation type}.
	 * @param annotationType the <em>annotation type</em> for which the default value should be retrieved
	 * @return the default value, or {@code null} if not found
	 * @see #getDefaultValue(Class, String)
	 */
	@Nullable
	public static Object getDefaultValue(Class<? extends Annotation> annotationType) {
		return getDefaultValue(annotationType, VALUE);
	}

	/**
	 * Retrieve the <em>default value</em> of a named attribute, given the
	 * {@link Class annotation type}.
	 * @param annotationType the <em>annotation type</em> for which the default value should be retrieved
	 * @param attributeName the name of the attribute value to retrieve.
	 * @return the default value of the named attribute, or {@code null} if not found
	 * @see #getDefaultValue(Annotation, String)
	 */
	@Nullable
	public static Object getDefaultValue(
			@Nullable Class<? extends Annotation> annotationType, @Nullable String attributeName) {

		if (annotationType == null || !StringUtils.hasText(attributeName)) {
			return null;
		}
		return MergedAnnotation.of(annotationType).getDefaultValue(attributeName).orElse(null);
	}

	/**
	 * <em>Synthesize</em> an annotation from the supplied {@code annotation}
	 * by wrapping it in a dynamic proxy that transparently enforces
	 * <em>attribute alias</em> semantics for annotation attributes that are
	 * annotated with {@link AliasFor @AliasFor}.
	 * @param annotation the annotation to synthesize
	 * @param annotatedElement the element that is annotated with the supplied
	 * annotation; may be {@code null} if unknown
	 * @return the synthesized annotation if the supplied annotation is
	 * <em>synthesizable</em>; {@code null} if the supplied annotation is
	 * {@code null}; otherwise the supplied annotation unmodified
	 * @throws AnnotationConfigurationException if invalid configuration of
	 * {@code @AliasFor} is detected
	 * @since 4.2
	 * @see #synthesizeAnnotation(Map, Class, AnnotatedElement)
	 * @see #synthesizeAnnotation(Class)
	 */
	public static <A extends Annotation> A synthesizeAnnotation(
			A annotation, @Nullable AnnotatedElement annotatedElement) {

		if (annotation instanceof SynthesizedAnnotation || AnnotationFilter.PLAIN.matches(annotation)) {
			return annotation;
		}
		return MergedAnnotation.from(annotatedElement, annotation).synthesize();
	}

	/**
	 * <em>Synthesize</em> an annotation from its default attributes values.
	 * <p>This method simply delegates to
	 * {@link #synthesizeAnnotation(Map, Class, AnnotatedElement)},
	 * supplying an empty map for the source attribute values and {@code null}
	 * for the {@link AnnotatedElement}.
	 * @param annotationType the type of annotation to synthesize
	 * @return the synthesized annotation
	 * @throws IllegalArgumentException if a required attribute is missing
	 * @throws AnnotationConfigurationException if invalid configuration of
	 * {@code @AliasFor} is detected
	 * @since 4.2
	 * @see #synthesizeAnnotation(Map, Class, AnnotatedElement)
	 * @see #synthesizeAnnotation(Annotation, AnnotatedElement)
	 */
	public static <A extends Annotation> A synthesizeAnnotation(Class<A> annotationType) {
		return synthesizeAnnotation(Collections.emptyMap(), annotationType, null);
	}

	/**
	 * <em>Synthesize</em> an annotation from the supplied map of annotation
	 * attributes by wrapping the map in a dynamic proxy that implements an
	 * annotation of the specified {@code annotationType} and transparently
	 * enforces <em>attribute alias</em> semantics for annotation attributes
	 * that are annotated with {@link AliasFor @AliasFor}.
	 * <p>The supplied map must contain a key-value pair for every attribute
	 * defined in the supplied {@code annotationType} that is not aliased or
	 * does not have a default value. Nested maps and nested arrays of maps
	 * will be recursively synthesized into nested annotations or nested
	 * arrays of annotations, respectively.
	 * <p>Note that {@link AnnotationAttributes} is a specialized type of
	 * {@link Map} that is an ideal candidate for this method's
	 * {@code attributes} argument.
	 * @param attributes the map of annotation attributes to synthesize
	 * @param annotationType the type of annotation to synthesize
	 * @param annotatedElement the element that is annotated with the annotation
	 * corresponding to the supplied attributes; may be {@code null} if unknown
	 * @return the synthesized annotation
	 * @throws IllegalArgumentException if a required attribute is missing or if an
	 * attribute is not of the correct type
	 * @throws AnnotationConfigurationException if invalid configuration of
	 * {@code @AliasFor} is detected
	 * @since 4.2
	 * @see #synthesizeAnnotation(Annotation, AnnotatedElement)
	 * @see #synthesizeAnnotation(Class)
	 * @see #getAnnotationAttributes(AnnotatedElement, Annotation)
	 * @see #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)
	 */
	public static <A extends Annotation> A synthesizeAnnotation(Map<String, Object> attributes,
			Class<A> annotationType, @Nullable AnnotatedElement annotatedElement) {

		try {
			return MergedAnnotation.of(annotatedElement, annotationType, attributes).synthesize();
		}
		catch (NoSuchElementException | IllegalStateException ex) {
			throw new IllegalArgumentException(ex);
		}
	}

	/**
	 * <em>Synthesize</em> an array of annotations from the supplied array
	 * of {@code annotations} by creating a new array of the same size and
	 * type and populating it with {@linkplain #synthesizeAnnotation(Annotation,
	 * AnnotatedElement) synthesized} versions of the annotations from the input
	 * array.
	 * @param annotations the array of annotations to synthesize
	 * @param annotatedElement the element that is annotated with the supplied
	 * array of annotations; may be {@code null} if unknown
	 * @return a new array of synthesized annotations, or {@code null} if
	 * the supplied array is {@code null}
	 * @throws AnnotationConfigurationException if invalid configuration of
	 * {@code @AliasFor} is detected
	 * @since 4.2
	 * @see #synthesizeAnnotation(Annotation, AnnotatedElement)
	 * @see #synthesizeAnnotation(Map, Class, AnnotatedElement)
	 */
	static Annotation[] synthesizeAnnotationArray(Annotation[] annotations, AnnotatedElement annotatedElement) {
		if (AnnotationsScanner.hasPlainJavaAnnotationsOnly(annotatedElement)) {
			return annotations;
		}
		Annotation[] synthesized = (Annotation[]) Array.newInstance(
				annotations.getClass().getComponentType(), annotations.length);
		for (int i = 0; i < annotations.length; i++) {
			synthesized[i] = synthesizeAnnotation(annotations[i], annotatedElement);
		}
		return synthesized;
	}

	/**
	 * Clear the internal annotation metadata cache.
	 * @since 4.3.15
	 */
	public static void clearCache() {
		AnnotationTypeMappings.clearCache();
		AnnotationsScanner.clearCache();
	}


	/**
	 * Internal holder used to wrap default values.
	 */
	private static class DefaultValueHolder {

		final Object defaultValue;

		public DefaultValueHolder(Object defaultValue) {
			this.defaultValue = defaultValue;
		}

		@Override
		public String toString() {
			return "*" + this.defaultValue;
		}
	}

}
