001/*
002 * Copyright 2002-2020 the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      https://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package org.springframework.beans.factory.support;
018
019import org.springframework.beans.BeanUtils;
020import org.springframework.beans.factory.config.BeanDefinitionHolder;
021import org.springframework.beans.factory.config.DependencyDescriptor;
022import org.springframework.lang.Nullable;
023
024/**
025 * Strategy interface for determining whether a specific bean definition
026 * qualifies as an autowire candidate for a specific dependency.
027 *
028 * @author Juergen Hoeller
029 * @author Mark Fisher
030 * @since 2.5
031 */
032public interface AutowireCandidateResolver {
033
034        /**
035         * Determine whether the given bean definition qualifies as an
036         * autowire candidate for the given dependency.
037         * <p>The default implementation checks
038         * {@link org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()}.
039         * @param bdHolder the bean definition including bean name and aliases
040         * @param descriptor the descriptor for the target method parameter or field
041         * @return whether the bean definition qualifies as autowire candidate
042         * @see org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()
043         */
044        default boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
045                return bdHolder.getBeanDefinition().isAutowireCandidate();
046        }
047
048        /**
049         * Determine whether the given descriptor is effectively required.
050         * <p>The default implementation checks {@link DependencyDescriptor#isRequired()}.
051         * @param descriptor the descriptor for the target method parameter or field
052         * @return whether the descriptor is marked as required or possibly indicating
053         * non-required status some other way (e.g. through a parameter annotation)
054         * @since 5.0
055         * @see DependencyDescriptor#isRequired()
056         */
057        default boolean isRequired(DependencyDescriptor descriptor) {
058                return descriptor.isRequired();
059        }
060
061        /**
062         * Determine whether the given descriptor declares a qualifier beyond the type
063         * (typically - but not necessarily - a specific kind of annotation).
064         * <p>The default implementation returns {@code false}.
065         * @param descriptor the descriptor for the target method parameter or field
066         * @return whether the descriptor declares a qualifier, narrowing the candidate
067         * status beyond the type match
068         * @since 5.1
069         * @see org.springframework.beans.factory.annotation.QualifierAnnotationAutowireCandidateResolver#hasQualifier
070         */
071        default boolean hasQualifier(DependencyDescriptor descriptor) {
072                return false;
073        }
074
075        /**
076         * Determine whether a default value is suggested for the given dependency.
077         * <p>The default implementation simply returns {@code null}.
078         * @param descriptor the descriptor for the target method parameter or field
079         * @return the value suggested (typically an expression String),
080         * or {@code null} if none found
081         * @since 3.0
082         */
083        @Nullable
084        default Object getSuggestedValue(DependencyDescriptor descriptor) {
085                return null;
086        }
087
088        /**
089         * Build a proxy for lazy resolution of the actual dependency target,
090         * if demanded by the injection point.
091         * <p>The default implementation simply returns {@code null}.
092         * @param descriptor the descriptor for the target method parameter or field
093         * @param beanName the name of the bean that contains the injection point
094         * @return the lazy resolution proxy for the actual dependency target,
095         * or {@code null} if straight resolution is to be performed
096         * @since 4.0
097         */
098        @Nullable
099        default Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, @Nullable String beanName) {
100                return null;
101        }
102
103        /**
104         * Return a clone of this resolver instance if necessary, retaining its local
105         * configuration and allowing for the cloned instance to get associated with
106         * a new bean factory, or this original instance if there is no such state.
107         * <p>The default implementation creates a separate instance via the default
108         * class constructor, assuming no specific configuration state to copy.
109         * Subclasses may override this with custom configuration state handling
110         * or with standard {@link Cloneable} support (as implemented by Spring's
111         * own configurable {@code AutowireCandidateResolver} variants), or simply
112         * return {@code this} (as in {@link SimpleAutowireCandidateResolver}).
113         * @since 5.2.7
114         * @see GenericTypeAwareAutowireCandidateResolver#cloneIfNecessary()
115         * @see DefaultListableBeanFactory#copyConfigurationFrom
116         */
117        default AutowireCandidateResolver cloneIfNecessary() {
118                return BeanUtils.instantiateClass(getClass());
119        }
120
121}