/*
 * Copyright 2002-2015 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
 *
 *      http://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.Method;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;

import org.springframework.core.BridgeMethodResolver;
import org.springframework.util.Assert;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

/**
 * General utility methods for finding annotations and meta-annotations on
 * {@link AnnotatedElement AnnotatedElements}.
 *
 * <p>{@code AnnotatedElementUtils} defines the public API for Spring's
 * meta-annotation programming model with support for <em>annotation attribute
 * overrides</em>. If you do not need support for annotation attribute
 * overrides, consider using {@link AnnotationUtils} instead.
 *
 * <p>Note that the features of this class are not provided by the JDK's
 * introspection facilities themselves.
 *
 * <h3>Annotation Attribute Overrides</h3>
 * <p>Support for meta-annotations with <em>attribute overrides</em> in
 * <em>composed annotations</em> is provided by all variants of the
 * {@code getMergedAnnotationAttributes()}, {@code getMergedAnnotation()},
 * {@code findMergedAnnotationAttributes()}, and {@code findMergedAnnotation()}
 * methods.
 *
 * <h3>Find vs. Get Semantics</h3>
 * <p>The search algorithms used by methods in this class follow either
 * <em>find</em> or <em>get</em> semantics. Consult the javadocs for each
 * individual method for details on which search algorithm is used.
 *
 * <p><strong>Get semantics</strong> are limited to searching for annotations
 * that are either <em>present</em> on an {@code AnnotatedElement} (i.e.,
 * declared locally or {@linkplain java.lang.annotation.Inherited inherited})
 * or declared within the annotation hierarchy <em>above</em> the
 * {@code AnnotatedElement}.
 *
 * <p><strong>Find semantics</strong> are much more exhaustive, providing
 * <em>get semantics</em> plus support for the following:
 *
 * <ul>
 * <li>Searching on interfaces, if the annotated element is a class
 * <li>Searching on superclasses, if the annotated element is a class
 * <li>Resolving bridged methods, if the annotated element is a method
 * <li>Searching on methods in interfaces, if the annotated element is a method
 * <li>Searching on methods in superclasses, if the annotated element is a method
 * </ul>
 *
 * <h3>Support for {@code @Inherited}</h3>
 * <p>Methods following <em>get semantics</em> will honor the contract of
 * Java's {@link java.lang.annotation.Inherited @Inherited} annotation except
 * that locally declared annotations (including custom composed annotations)
 * will be favored over inherited annotations. In contrast, methods following
 * <em>find semantics</em> will completely ignore the presence of
 * {@code @Inherited} since the <em>find</em> search algorithm manually
 * traverses type and method hierarchies and thereby implicitly supports
 * annotation inheritance without the need for {@code @Inherited}.
 *
 * @author Phillip Webb
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 4.0
 * @see AliasFor
 * @see AnnotationAttributes
 * @see AnnotationUtils
 * @see BridgeMethodResolver
 */
public class AnnotatedElementUtils {

	private static final Boolean CONTINUE = null;


	/**
	 * Get the fully qualified class names of all meta-annotation types
	 * <em>present</em> on the annotation (of the specified {@code annotationType})
	 * on the supplied {@link AnnotatedElement}.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @return the names of all meta-annotations present on the annotation,
	 * or {@code null} if not found
	 * @since 4.2
	 * @see #getMetaAnnotationTypes(AnnotatedElement, String)
	 * @see #hasMetaAnnotationTypes
	 */
	public static Set<String> getMetaAnnotationTypes(AnnotatedElement element, Class<? extends Annotation> annotationType) {
		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.notNull(annotationType, "annotationType must not be null");
		final Set<String> types = new LinkedHashSet<String>();

		try {
			Annotation annotation = element.getAnnotation(annotationType);
			if (annotation != null) {
				searchWithGetSemantics(annotation.annotationType(), annotationType, null, new SimpleAnnotationProcessor<Object>() {
					@Override
					public Object process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
						types.add(annotation.annotationType().getName());
						return CONTINUE;
					}
				}, new HashSet<AnnotatedElement>(), 1);
			}
		}
		catch (Throwable ex) {
			AnnotationUtils.rethrowAnnotationConfigurationException(ex);
			throw new IllegalStateException("Failed to introspect annotations on " + element, ex);
		}

		return (!types.isEmpty() ? types : null);
	}

	/**
	 * Get the fully qualified class names of all meta-annotation
	 * types <em>present</em> on the annotation (of the specified
	 * {@code annotationName}) on the supplied {@link AnnotatedElement}.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation
	 * type on which to find meta-annotations
	 * @return the names of all meta-annotations present on the annotation,
	 * or {@code null} if not found
	 * @see #getMetaAnnotationTypes(AnnotatedElement, Class)
	 * @see #hasMetaAnnotationTypes
	 */
	public static Set<String> getMetaAnnotationTypes(AnnotatedElement element, String annotationName) {
		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.hasLength(annotationName, "annotationName must not be null or empty");
		final Set<String> types = new LinkedHashSet<String>();

		try {
			Annotation annotation = AnnotationUtils.getAnnotation(element, annotationName);
			if (annotation != null) {
				searchWithGetSemantics(annotation.annotationType(), null, annotationName, new SimpleAnnotationProcessor<Object>() {
					@Override
					public Object process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
						types.add(annotation.annotationType().getName());
						return CONTINUE;
					}
				}, new HashSet<AnnotatedElement>(), 1);
			}
		}
		catch (Throwable ex) {
			AnnotationUtils.rethrowAnnotationConfigurationException(ex);
			throw new IllegalStateException("Failed to introspect annotations on " + element, ex);
		}

		return (!types.isEmpty() ? types : null);
	}

	/**
	 * Determine if the supplied {@link AnnotatedElement} is annotated with
	 * a <em>composed annotation</em> that is meta-annotated with an
	 * annotation of the specified {@code annotationName}.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @return {@code true} if a matching meta-annotation is present
	 * @since 4.2.3
	 * @see #getMetaAnnotationTypes
	 */
	public static boolean hasMetaAnnotationTypes(AnnotatedElement element, final Class<? extends Annotation> annotationType) {
		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.notNull(annotationType, "annotationType must not be null");

		return Boolean.TRUE.equals(searchWithGetSemantics(element, annotationType, null, new SimpleAnnotationProcessor<Boolean>() {
			@Override
			public Boolean process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
				boolean found = (annotation.annotationType() == annotationType);
				return (found && metaDepth > 0 ? Boolean.TRUE : CONTINUE);
			}
		}));
	}

	/**
	 * Determine if the supplied {@link AnnotatedElement} is annotated with a
	 * <em>composed annotation</em> that is meta-annotated with an annotation
	 * of the specified {@code annotationName}.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the
	 * meta-annotation type to find
	 * @return {@code true} if a matching meta-annotation is present
	 * @see #getMetaAnnotationTypes
	 */
	public static boolean hasMetaAnnotationTypes(AnnotatedElement element, final String annotationName) {
		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.hasLength(annotationName, "annotationName must not be null or empty");

		return Boolean.TRUE.equals(searchWithGetSemantics(element, null, annotationName, new SimpleAnnotationProcessor<Boolean>() {
			@Override
			public Boolean process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
				boolean found = annotation.annotationType().getName().equals(annotationName);
				return (found && metaDepth > 0 ? Boolean.TRUE : CONTINUE);
			}
		}));
	}

	/**
	 * Determine if an annotation of the specified {@code annotationName}
	 * is <em>present</em> on the supplied {@link AnnotatedElement} or
	 * within the annotation hierarchy <em>above</em> the specified element.
	 * <p>If this method returns {@code true}, then {@link #getMergedAnnotationAttributes}
	 * will return a non-null value.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @return {@code true} if a matching annotation is present
	 * @since 4.2.3
	 */
	public static boolean isAnnotated(AnnotatedElement element, final Class<? extends Annotation> annotationType) {
		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.notNull(annotationType, "annotationType must not be null");

		return Boolean.TRUE.equals(searchWithGetSemantics(element, annotationType, null, new SimpleAnnotationProcessor<Boolean>() {
			@Override
			public Boolean process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
				boolean found = annotation.annotationType() == annotationType;
				return (found ? Boolean.TRUE : CONTINUE);
			}
		}));
	}

	/**
	 * Determine if an annotation of the specified {@code annotationName} is
	 * <em>present</em> on the supplied {@link AnnotatedElement} or within the
	 * annotation hierarchy <em>above</em> the specified element.
	 * <p>If this method returns {@code true}, then {@link #getMergedAnnotationAttributes}
	 * will return a non-null value.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @return {@code true} if a matching annotation is present
	 */
	public static boolean isAnnotated(AnnotatedElement element, final String annotationName) {
		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.hasLength(annotationName, "annotationName must not be null or empty");

		return Boolean.TRUE.equals(searchWithGetSemantics(element, null, annotationName, new SimpleAnnotationProcessor<Boolean>() {
			@Override
			public Boolean process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
				boolean found = annotation.annotationType().getName().equals(annotationName);
				return (found ? Boolean.TRUE : CONTINUE);
			}
		}));
	}

	/**
	 * Get the first annotation of the specified {@code annotationType} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element},
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy, and synthesize
	 * the result back into an annotation of the specified {@code annotationType}.
	 * <p>{@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * <p>This method delegates to {@link #getMergedAnnotationAttributes(AnnotatedElement, Class)}
	 * and {@link AnnotationUtils#synthesizeAnnotation(Map, Class, AnnotatedElement)}.
	 * @param element the annotated element
	 * @param annotationType the annotation type to find
	 * @return the merged, synthesized {@code Annotation}, or {@code null} if not found
	 * @since 4.2
	 * @see #getMergedAnnotationAttributes(AnnotatedElement, Class)
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 * @see AnnotationUtils#synthesizeAnnotation(Map, Class, AnnotatedElement)
	 */
	public static <A extends Annotation> A getMergedAnnotation(AnnotatedElement element, Class<A> annotationType) {
		AnnotationAttributes attributes = getMergedAnnotationAttributes(element, annotationType);
		return AnnotationUtils.synthesizeAnnotation(attributes, annotationType, element);
	}

	/**
	 * Get the first annotation of the specified {@code annotationType} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element} and
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy.
	 * <p>{@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * <p>This method delegates to {@link #getMergedAnnotationAttributes(AnnotatedElement, String)}.
	 * @param element the annotated element
	 * @param annotationType the annotation type to find
	 * @return the merged {@code AnnotationAttributes}, or {@code null} if not found
	 * @since 4.2
	 * @see #getMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see #findMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see #getMergedAnnotation(AnnotatedElement, Class)
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 */
	public static AnnotationAttributes getMergedAnnotationAttributes(
			AnnotatedElement element, Class<? extends Annotation> annotationType) {

		Assert.notNull(annotationType, "annotationType must not be null");
		AnnotationAttributes attributes = searchWithGetSemantics(element, annotationType, null,
				new MergedAnnotationAttributesProcessor(annotationType, null, false, false));
		AnnotationUtils.postProcessAnnotationAttributes(element, attributes, false, false);
		return attributes;
	}

	/**
	 * Get the first annotation of the specified {@code annotationName} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element} and
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy.
	 * <p>{@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * <p>This method delegates to {@link #getMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)},
	 * supplying {@code false} for {@code classValuesAsString} and {@code nestedAnnotationsAsMap}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @return the merged {@code AnnotationAttributes}, or {@code null} if not found
	 * @since 4.2
	 * @see #getMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see #findMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 * @see #getAllAnnotationAttributes(AnnotatedElement, String)
	 */
	public static AnnotationAttributes getMergedAnnotationAttributes(AnnotatedElement element, String annotationName) {
		return getMergedAnnotationAttributes(element, annotationName, false, false);
	}

	/**
	 * Get the first annotation of the specified {@code annotationName} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element} and
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy.
	 * <p>Attributes from lower levels in the annotation hierarchy override attributes
	 * of the same name from higher levels, and {@link AliasFor @AliasFor} semantics are
	 * fully supported, both within a single annotation and within the annotation hierarchy.
	 * <p>In contrast to {@link #getAllAnnotationAttributes}, the search algorithm used by
	 * this method will stop searching the annotation hierarchy once the first annotation
	 * of the specified {@code annotationName} has been found. As a consequence,
	 * additional annotations of the specified {@code annotationName} will be ignored.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @param classValuesAsString whether to convert Class references into Strings or to
	 * preserve them as Class references
	 * @param nestedAnnotationsAsMap whether to convert nested Annotation instances
	 * into {@code AnnotationAttributes} maps or to preserve them as Annotation instances
	 * @return the merged {@code AnnotationAttributes}, or {@code null} if not found
	 * @since 4.2
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 * @see #findMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see #getAllAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 */
	public static AnnotationAttributes getMergedAnnotationAttributes(AnnotatedElement element,
			String annotationName, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

		AnnotationAttributes attributes = searchWithGetSemantics(element, null, annotationName,
				new MergedAnnotationAttributesProcessor(null, annotationName, classValuesAsString, nestedAnnotationsAsMap));
		AnnotationUtils.postProcessAnnotationAttributes(element, attributes, classValuesAsString, nestedAnnotationsAsMap);
		return attributes;
	}

	/**
	 * Find the first annotation of the specified {@code annotationType} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element},
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy, and synthesize
	 * the result back into an annotation of the specified {@code annotationType}.
	 * <p>{@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * @param element the annotated element
	 * @param annotationType the annotation type to find
	 * @return the merged, synthesized {@code Annotation}, or {@code null} if not found
	 * @since 4.2
	 * @see #findMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see #getMergedAnnotationAttributes(AnnotatedElement, Class)
	 */
	public static <A extends Annotation> A findMergedAnnotation(AnnotatedElement element, Class<A> annotationType) {
		Assert.notNull(annotationType, "annotationType must not be null");
		AnnotationAttributes attributes = findMergedAnnotationAttributes(element, annotationType, false, false);
		return AnnotationUtils.synthesizeAnnotation(attributes, annotationType, element);
	}

	/**
	 * Find the first annotation of the specified {@code annotationName} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element},
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy, and synthesize
	 * the result back into an annotation of the specified {@code annotationName}.
	 * <p>{@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * <p>This method delegates to {@link #findMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)}
	 * (supplying {@code false} for {@code classValuesAsString} and {@code nestedAnnotationsAsMap})
	 * and {@link AnnotationUtils#synthesizeAnnotation(Map, Class, AnnotatedElement)}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @return the merged, synthesized {@code Annotation}, or {@code null} if not found
	 * @since 4.2
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 * @see #findMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 * @see AnnotationUtils#synthesizeAnnotation(Map, Class, AnnotatedElement)
	 * @deprecated As of Spring Framework 4.2.3, use {@link #findMergedAnnotation(AnnotatedElement, Class)} instead.
	 */
	@Deprecated
	@SuppressWarnings("unchecked")
	public static <A extends Annotation> A findMergedAnnotation(AnnotatedElement element, String annotationName) {
		AnnotationAttributes attributes = findMergedAnnotationAttributes(element, annotationName, false, false);
		return AnnotationUtils.synthesizeAnnotation(attributes, (Class<A>) attributes.annotationType(), element);
	}

	/**
	 * Find the first annotation of the specified {@code annotationName} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element} and
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy.
	 * <p>Attributes from lower levels in the annotation hierarchy override
	 * attributes of the same name from higher levels, and
	 * {@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * <p>In contrast to {@link #getAllAnnotationAttributes}, the search
	 * algorithm used by this method will stop searching the annotation
	 * hierarchy once the first annotation of the specified
	 * {@code annotationName} has been found. As a consequence, additional
	 * annotations of the specified {@code annotationName} will be ignored.
	 * <p>This method follows <em>find semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationType the annotation type to find
	 * @param classValuesAsString whether to convert Class references into
	 * Strings or to preserve them as Class references
	 * @param nestedAnnotationsAsMap whether to convert nested Annotation
	 * instances into {@code AnnotationAttributes} maps or to preserve them
	 * as Annotation instances
	 * @return the merged {@code AnnotationAttributes}, or {@code null} if
	 * not found
	 * @since 4.2
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 * @see #getMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 */
	public static AnnotationAttributes findMergedAnnotationAttributes(AnnotatedElement element,
			Class<? extends Annotation> annotationType, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

		AnnotationAttributes attributes = searchWithFindSemantics(element, annotationType, annotationType.getName(),
				new MergedAnnotationAttributesProcessor(annotationType, null, classValuesAsString, nestedAnnotationsAsMap));
		AnnotationUtils.postProcessAnnotationAttributes(element, attributes, classValuesAsString, nestedAnnotationsAsMap);
		return attributes;
	}

	/**
	 * Find the first annotation of the specified {@code annotationName} within
	 * the annotation hierarchy <em>above</em> the supplied {@code element} and
	 * merge that annotation's attributes with <em>matching</em> attributes from
	 * annotations in lower levels of the annotation hierarchy.
	 * <p>Attributes from lower levels in the annotation hierarchy override
	 * attributes of the same name from higher levels, and
	 * {@link AliasFor @AliasFor} semantics are fully supported, both
	 * within a single annotation and within the annotation hierarchy.
	 * <p>In contrast to {@link #getAllAnnotationAttributes}, the search
	 * algorithm used by this method will stop searching the annotation
	 * hierarchy once the first annotation of the specified
	 * {@code annotationName} has been found. As a consequence, additional
	 * annotations of the specified {@code annotationName} will be ignored.
	 * <p>This method follows <em>find semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @param classValuesAsString whether to convert Class references into Strings or to
	 * preserve them as Class references
	 * @param nestedAnnotationsAsMap whether to convert nested Annotation instances into
	 * {@code AnnotationAttributes} maps or to preserve them as Annotation instances
	 * @return the merged {@code AnnotationAttributes}, or {@code null} if not found
	 * @since 4.2
	 * @see #findMergedAnnotation(AnnotatedElement, Class)
	 * @see #getMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 */
	public static AnnotationAttributes findMergedAnnotationAttributes(AnnotatedElement element,
			String annotationName, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

		AnnotationAttributes attributes = searchWithFindSemantics(element, null, annotationName,
				new MergedAnnotationAttributesProcessor(null, annotationName, classValuesAsString, nestedAnnotationsAsMap));
		AnnotationUtils.postProcessAnnotationAttributes(element, attributes, classValuesAsString, nestedAnnotationsAsMap);
		return attributes;
	}

	/**
	 * @deprecated As of Spring Framework 4.2, use {@link #getMergedAnnotationAttributes(AnnotatedElement, String)} instead.
	 */
	@Deprecated
	public static AnnotationAttributes getAnnotationAttributes(AnnotatedElement element, String annotationName) {
		return getMergedAnnotationAttributes(element, annotationName);
	}

	/**
	 * @deprecated As of Spring Framework 4.2, use {@link #getMergedAnnotationAttributes(AnnotatedElement, String, boolean, boolean)} instead.
	 */
	@Deprecated
	public static AnnotationAttributes getAnnotationAttributes(AnnotatedElement element, String annotationName,
			boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

		return getMergedAnnotationAttributes(element, annotationName, classValuesAsString, nestedAnnotationsAsMap);
	}

	/**
	 * Get the annotation attributes of <strong>all</strong> annotations of the specified
	 * {@code annotationName} in the annotation hierarchy above the supplied
	 * {@link AnnotatedElement} and store the results in a {@link MultiValueMap}.
	 * <p>Note: in contrast to {@link #getMergedAnnotationAttributes(AnnotatedElement, String)},
	 * this method does <em>not</em> support attribute overrides.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @return a {@link MultiValueMap} keyed by attribute name, containing the annotation
	 * attributes from all annotations found, or {@code null} if not found
	 * @see #getAllAnnotationAttributes(AnnotatedElement, String, boolean, boolean)
	 */
	public static MultiValueMap<String, Object> getAllAnnotationAttributes(AnnotatedElement element, String annotationName) {
		return getAllAnnotationAttributes(element, annotationName, false, false);
	}

	/**
	 * Get the annotation attributes of <strong>all</strong> annotations of
	 * the specified {@code annotationName} in the annotation hierarchy above
	 * the supplied {@link AnnotatedElement} and store the results in a
	 * {@link MultiValueMap}.
	 * <p>Note: in contrast to {@link #getMergedAnnotationAttributes(AnnotatedElement, String)},
	 * this method does <em>not</em> support attribute overrides.
	 * <p>This method follows <em>get semantics</em> as described in the
	 * {@linkplain AnnotatedElementUtils class-level javadoc}.
	 * @param element the annotated element
	 * @param annotationName the fully qualified class name of the annotation type to find
	 * @param classValuesAsString whether to convert Class references into Strings or to
	 * preserve them as Class references
	 * @param nestedAnnotationsAsMap whether to convert nested Annotation instances into
	 * {@code AnnotationAttributes} maps or to preserve them as Annotation instances
	 * @return a {@link MultiValueMap} keyed by attribute name, containing the annotation
	 * attributes from all annotations found, or {@code null} if not found
	 */
	public static MultiValueMap<String, Object> getAllAnnotationAttributes(AnnotatedElement element,
			final String annotationName, final boolean classValuesAsString, final boolean nestedAnnotationsAsMap) {

		final MultiValueMap<String, Object> attributesMap = new LinkedMultiValueMap<String, Object>();

		searchWithGetSemantics(element, null, annotationName, new SimpleAnnotationProcessor<Void>() {
			@Override
			public Void process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
				boolean found = annotation.annotationType().getName().equals(annotationName);
				if (found) {
					AnnotationAttributes annotationAttributes = AnnotationUtils.getAnnotationAttributes(
							annotation, classValuesAsString, nestedAnnotationsAsMap);
					for (Map.Entry<String, Object> entry : annotationAttributes.entrySet()) {
						attributesMap.add(entry.getKey(), entry.getValue());
					}
				}
				// Continue searching...
				return null;
			}
		});

		return (!attributesMap.isEmpty() ? attributesMap : null);
	}

	/**
	 * Search for annotations of the specified {@code annotationName} on
	 * the specified {@code element}, following <em>get semantics</em>.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @param annotationName the fully qualified class name of the annotation
	 * type to find (as an alternative to {@code annotationType})
	 * @param processor the processor to delegate to
	 * @return the result of the processor, potentially {@code null}
	 */
	private static <T> T searchWithGetSemantics(AnnotatedElement element,
			Class<? extends Annotation> annotationType, String annotationName, Processor<T> processor) {

		try {
			return searchWithGetSemantics(
					element, annotationType, annotationName, processor, new HashSet<AnnotatedElement>(), 0);
		}
		catch (Throwable ex) {
			AnnotationUtils.rethrowAnnotationConfigurationException(ex);
			throw new IllegalStateException("Failed to introspect annotations on " + element, ex);
		}
	}

	/**
	 * Perform the search algorithm for the {@link #searchWithGetSemantics}
	 * method, avoiding endless recursion by tracking which annotated elements
	 * have already been <em>visited</em>.
	 * <p>The {@code metaDepth} parameter is explained in the
	 * {@link Processor#process process()} method of the {@link Processor} API.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @param annotationName the fully qualified class name of the annotation
	 * type to find (as an alternative to {@code annotationType})
	 * @param processor the processor to delegate to
	 * @param visited the set of annotated elements that have already been visited
	 * @param metaDepth the meta-depth of the annotation
	 * @return the result of the processor, potentially {@code null}
	 */
	private static <T> T searchWithGetSemantics(AnnotatedElement element,
			Class<? extends Annotation> annotationType, String annotationName,
			Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth) {

		Assert.notNull(element, "AnnotatedElement must not be null");

		if (visited.add(element)) {
			try {
				// Start searching within locally declared annotations
				List<Annotation> declaredAnnotations = Arrays.asList(element.getDeclaredAnnotations());
				T result = searchWithGetSemanticsInAnnotations(element, declaredAnnotations,
						annotationType, annotationName, processor, visited, metaDepth);
				if (result != null) {
					return result;
				}

				if (element instanceof Class) {  //  otherwise getAnnotations doesn't return anything new
					List<Annotation> inheritedAnnotations = new ArrayList<Annotation>();
					for (Annotation annotation : element.getAnnotations()) {
						if (!declaredAnnotations.contains(annotation)) {
							inheritedAnnotations.add(annotation);
						}
					}

					// Continue searching within inherited annotations
					result = searchWithGetSemanticsInAnnotations(element, inheritedAnnotations,
							annotationType, annotationName, processor, visited, metaDepth);
					if (result != null) {
						return result;
					}
				}
			}
			catch (Exception ex) {
				AnnotationUtils.handleIntrospectionFailure(element, ex);
			}
		}

		return null;
	}

	/**
	 * This method is invoked by
	 * {@link #searchWithGetSemantics(AnnotatedElement, Class, String, Processor, Set, int)}
	 * to perform the actual search within the supplied list of annotations.
	 * <p>This method should be invoked first with locally declared annotations
	 * and then subsequently with inherited annotations, thereby allowing
	 * local annotations to take precedence over inherited annotations.
	 * <p>The {@code metaDepth} parameter is explained in the
	 * {@link Processor#process process()} method of the {@link Processor} API.
	 * @param annotatedElement the element that is annotated with the supplied
	 * annotations, used for contextual logging; may be {@code null} if unknown
	 * @param annotations the annotations to search in
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @param annotationName the fully qualified class name of the annotation
	 * type to find (as an alternative to {@code annotationType})
	 * @param processor the processor to delegate to
	 * @param visited the set of annotated elements that have already been visited
	 * @param metaDepth the meta-depth of the annotation
	 * @return the result of the processor, potentially {@code null}
	 * @since 4.2
	 */
	private static <T> T searchWithGetSemanticsInAnnotations(AnnotatedElement annotatedElement,
			List<Annotation> annotations, Class<? extends Annotation> annotationType, String annotationName,
			Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth) {

		// Search in annotations
		for (Annotation annotation : annotations) {
			if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation) &&
					((annotationType != null ? annotation.annotationType() == annotationType :
					annotation.annotationType().getName().equals(annotationName)) ||
					metaDepth > 0)) {
				T result = processor.process(annotatedElement, annotation, metaDepth);
				if (result != null) {
					return result;
				}
			}
		}

		// Recursively search in meta-annotations
		for (Annotation annotation : annotations) {
			if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
				T result = searchWithGetSemantics(annotation.annotationType(), annotationType,
						annotationName, processor, visited, metaDepth + 1);
				if (result != null) {
					processor.postProcess(annotatedElement, annotation, result);
					return result;
				}
			}
		}

		return null;
	}

	/**
	 * Search for annotations of the specified {@code annotationName} on
	 * the specified {@code element}, following <em>find semantics</em>.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @param annotationName the fully qualified class name of the annotation
	 * type to find (as an alternative to {@code annotationType})
	 * @param processor the processor to delegate to
	 * @return the result of the processor, potentially {@code null}
	 * @since 4.2
	 */
	private static <T> T searchWithFindSemantics(
			AnnotatedElement element, Class<? extends Annotation> annotationType, String annotationName, Processor<T> processor) {

		try {
			return searchWithFindSemantics(
					element, annotationType, annotationName, processor, new HashSet<AnnotatedElement>(), 0);
		}
		catch (Throwable ex) {
			AnnotationUtils.rethrowAnnotationConfigurationException(ex);
			throw new IllegalStateException("Failed to introspect annotations on " + element, ex);
		}
	}

	/**
	 * Perform the search algorithm for the {@link #searchWithFindSemantics}
	 * method, avoiding endless recursion by tracking which annotated elements
	 * have already been <em>visited</em>.
	 * <p>The {@code metaDepth} parameter is explained in the
	 * {@link Processor#process process()} method of the {@link Processor} API.
	 * @param element the annotated element
	 * @param annotationType the annotation type on which to find meta-annotations
	 * @param annotationName the fully qualified class name of the annotation
	 * type to find (as an alternative to {@code annotationType})
	 * @param processor the processor to delegate to
	 * @param visited the set of annotated elements that have already been visited
	 * @param metaDepth the meta-depth of the annotation
	 * @return the result of the processor, potentially {@code null}
	 * @since 4.2
	 */
	private static <T> T searchWithFindSemantics(AnnotatedElement element, Class<? extends Annotation> annotationType,
			String annotationName, Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth) {

		Assert.notNull(element, "AnnotatedElement must not be null");
		Assert.hasLength(annotationName, "annotationName must not be null or empty");

		if (visited.add(element)) {
			try {
				// Locally declared annotations (ignoring @Inherited)
				Annotation[] annotations = element.getDeclaredAnnotations();

				// Search in local annotations
				for (Annotation annotation : annotations) {
					if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation) &&
							((annotationType != null ? annotation.annotationType() == annotationType :
							annotation.annotationType().getName().equals(annotationName)) ||
							metaDepth > 0)) {
						T result = processor.process(element, annotation, metaDepth);
						if (result != null) {
							return result;
						}
					}
				}

				// Search in meta annotations on local annotations
				for (Annotation annotation : annotations) {
					if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
						T result = searchWithFindSemantics(
								annotation.annotationType(), annotationType, annotationName, processor, visited, metaDepth + 1);
						if (result != null) {
							processor.postProcess(annotation.annotationType(), annotation, result);
							return result;
						}
					}
				}

				if (element instanceof Method) {
					Method method = (Method) element;

					// Search on possibly bridged method
					Method resolvedMethod = BridgeMethodResolver.findBridgedMethod(method);
					T result = searchWithFindSemantics(resolvedMethod, annotationType, annotationName,
							processor, visited, metaDepth);
					if (result != null) {
						return result;
					}

					// Search on methods in interfaces declared locally
					Class<?>[] ifcs = method.getDeclaringClass().getInterfaces();
					result = searchOnInterfaces(
							method, annotationType, annotationName, processor, visited, metaDepth, ifcs);
					if (result != null) {
						return result;
					}

					// Search on methods in class hierarchy and interface hierarchy
					Class<?> clazz = method.getDeclaringClass();
					while (true) {
						clazz = clazz.getSuperclass();
						if (clazz == null || Object.class == clazz) {
							break;
						}

						try {
							Method equivalentMethod = clazz.getDeclaredMethod(method.getName(), method.getParameterTypes());
							Method resolvedEquivalentMethod = BridgeMethodResolver.findBridgedMethod(equivalentMethod);
							result = searchWithFindSemantics(resolvedEquivalentMethod, annotationType, annotationName,
									processor, visited, metaDepth);
							if (result != null) {
								return result;
							}
						}
						catch (NoSuchMethodException ex) {
							// No equivalent method found
						}

						// Search on interfaces declared on superclass
						result = searchOnInterfaces(method, annotationType, annotationName, processor, visited,
								metaDepth, clazz.getInterfaces());
						if (result != null) {
							return result;
						}
					}
				}

				if (element instanceof Class) {
					Class<?> clazz = (Class<?>) element;

					// Search on interfaces
					for (Class<?> ifc : clazz.getInterfaces()) {
						T result = searchWithFindSemantics(
								ifc, annotationType, annotationName, processor, visited, metaDepth);
						if (result != null) {
							return result;
						}
					}

					// Search on superclass
					Class<?> superclass = clazz.getSuperclass();
					if (superclass != null && Object.class != superclass) {
						T result = searchWithFindSemantics(
								superclass, annotationType, annotationName, processor, visited, metaDepth);
						if (result != null) {
							return result;
						}
					}
				}
			}
			catch (Exception ex) {
				AnnotationUtils.handleIntrospectionFailure(element, ex);
			}
		}
		return null;
	}

	private static <T> T searchOnInterfaces(Method method, Class<? extends Annotation> annotationType, String annotationName,
			Processor<T> processor, Set<AnnotatedElement> visited, int metaDepth, Class<?>[] ifcs) {

		for (Class<?> iface : ifcs) {
			if (AnnotationUtils.isInterfaceWithAnnotatedMethods(iface)) {
				try {
					Method equivalentMethod = iface.getMethod(method.getName(), method.getParameterTypes());
					T result = searchWithFindSemantics(equivalentMethod, annotationType, annotationName,
							processor, visited, metaDepth);
					if (result != null) {
						return result;
					}
				}
				catch (NoSuchMethodException ex) {
					// Skip this interface - it doesn't have the method...
				}
			}
		}

		return null;
	}


	/**
	 * Callback interface that is used to process annotations during a search.
	 * <p>Depending on the use case, a processor may choose to
	 * {@linkplain #process} a single target annotation, multiple target
	 * annotations, or all annotations discovered by the currently executing
	 * search. The term "target" in this context refers to a matching
	 * annotation (i.e., a specific annotation type that was found during
	 * the search). Returning a non-null value from the {@link #process}
	 * method instructs the search algorithm to stop searching further;
	 * whereas, returning {@code null} from the {@link #process} method
	 * instructs the search algorithm to continue searching for additional
	 * annotations.
	 * <p>Processors can optionally {@linkplain #postProcess post-process}
	 * the result of the {@link #process} method as the search algorithm
	 * goes back down the annotation hierarchy from an invocation of
	 * {@link #process} that returned a non-null value down to the
	 * {@link AnnotatedElement} that was supplied as the starting point to
	 * the search algorithm.
	 * @param <T> the type of result returned by the processor
	 */
	private interface Processor<T> {

		/**
		 * Process the supplied annotation.
		 * <p>Depending on the use case, the supplied annotation may be an
		 * actual target annotation that has been found by the search
		 * algorithm, or it may be some other annotation within the
		 * annotation hierarchy. In the latter case, the {@code metaDepth}
		 * should have a value greater than {@code 0}. In any case, it is
		 * up to concrete implementations of this method to decide what to
		 * do with the supplied annotation.
		 * <p>The {@code metaDepth} parameter represents the depth of the
		 * annotation relative to the first annotated element in the
		 * annotation hierarchy. For example, an annotation that is
		 * <em>present</em> on a non-annotation element will have a depth
		 * of 0; a meta-annotation will have a depth of 1; and a
		 * meta-meta-annotation will have a depth of 2; etc.
		 * @param annotatedElement the element that is annotated with the
		 * supplied annotation, used for contextual logging; may be
		 * {@code null} if unknown
		 * @param annotation the annotation to process
		 * @param metaDepth the meta-depth of the annotation
		 * @return the result of the processing, or {@code null} to continue
		 * searching for additional annotations
		 */
		T process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth);

		/**
		 * Post-process the result returned by the {@link #process} method.
		 * <p>The {@code annotation} supplied to this method is an annotation
		 * that is present in the annotation hierarchy, between the initial
		 * {@link AnnotatedElement} and an invocation of {@link #process}
		 * that returned a non-null value.
		 * @param annotatedElement the element that is annotated with the
		 * supplied annotation, used for contextual logging; may be
		 * {@code null} if unknown
		 * @param annotation the annotation to post-process
		 * @param result the result to post-process
		 */
		void postProcess(AnnotatedElement annotatedElement, Annotation annotation, T result);
	}


	/**
	 * {@link Processor} that {@linkplain #process processes} annotations
	 * but does not {@linkplain #postProcess post-process} results.
	 * @since 4.2
	 */
	private abstract static class SimpleAnnotationProcessor<T> implements Processor<T> {

		@Override
		public final void postProcess(AnnotatedElement annotatedElement, Annotation annotation, T result) {
			// no-op
		}
	}


	/**
	 * {@link Processor} that gets the {@code AnnotationAttributes} for the
	 * target annotation during the {@link #process} phase and then merges
	 * annotation attributes from lower levels in the annotation hierarchy
	 * during the {@link #postProcess} phase.
	 * @since 4.2
	 * @see AnnotationUtils#retrieveAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)
	 * @see AnnotationUtils#postProcessAnnotationAttributes
	 */
	private static class MergedAnnotationAttributesProcessor implements Processor<AnnotationAttributes> {

		private final Class<? extends Annotation> annotationType;

		private final String annotationName;

		private final boolean classValuesAsString;

		private final boolean nestedAnnotationsAsMap;

		MergedAnnotationAttributesProcessor(Class<? extends Annotation> annotationType, String annotationName,
				boolean classValuesAsString, boolean nestedAnnotationsAsMap) {

			this.annotationType = annotationType;
			this.annotationName = annotationName;
			this.classValuesAsString = classValuesAsString;
			this.nestedAnnotationsAsMap = nestedAnnotationsAsMap;
		}

		@Override
		public AnnotationAttributes process(AnnotatedElement annotatedElement, Annotation annotation, int metaDepth) {
			boolean found = (this.annotationType != null ? annotation.annotationType() == this.annotationType :
					annotation.annotationType().getName().equals(this.annotationName));
			return (found ? AnnotationUtils.retrieveAnnotationAttributes(annotatedElement, annotation,
					this.classValuesAsString, this.nestedAnnotationsAsMap) : null);
		}

		@Override
		public void postProcess(AnnotatedElement element, Annotation annotation, AnnotationAttributes attributes) {
			annotation = AnnotationUtils.synthesizeAnnotation(annotation, element);
			Class<? extends Annotation> targetAnnotationType = attributes.annotationType();

			for (Method attributeMethod : AnnotationUtils.getAttributeMethods(annotation.annotationType())) {
				String attributeName = attributeMethod.getName();
				String attributeOverrideName = AnnotationUtils.getAttributeOverrideName(attributeMethod, targetAnnotationType);

				// Explicit annotation attribute override declared via @AliasFor
				if (attributeOverrideName != null) {
					if (attributes.containsKey(attributeOverrideName)) {
						overrideAttribute(element, annotation, attributes, attributeName, attributeOverrideName);
					}
				}
				// Implicit annotation attribute override based on convention
				else if (!AnnotationUtils.VALUE.equals(attributeName) && attributes.containsKey(attributeName)) {
					overrideAttribute(element, annotation, attributes, attributeName, attributeName);
				}
			}
		}

		private void overrideAttribute(AnnotatedElement element, Annotation annotation,
				AnnotationAttributes attributes, String sourceAttributeName, String targetAttributeName) {

			Object value = AnnotationUtils.getValue(annotation, sourceAttributeName);
			Object adaptedValue = AnnotationUtils.adaptValue(
					element, value, this.classValuesAsString, this.nestedAnnotationsAsMap);
			attributes.put(targetAttributeName, adaptedValue);
		}
	}

}
