org.springframework.beans.factory.support.AutowireCandidateResolver.java Source code

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Here is the source code for org.springframework.beans.factory.support.AutowireCandidateResolver.java

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/*
 * Copyright 2002-2018 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.beans.factory.support;

import org.springframework.beans.factory.config.BeanDefinitionHolder;
import org.springframework.beans.factory.config.DependencyDescriptor;
import org.springframework.lang.Nullable;

/**
 * Strategy interface for determining whether a specific bean definition
 * qualifies as an autowire candidate for a specific dependency.
 *
 * @author Juergen Hoeller
 * @author Mark Fisher
 * @since 2.5
 */
public interface AutowireCandidateResolver {

    /**
     * Determine whether the given bean definition qualifies as an
     * autowire candidate for the given dependency.
     * <p>The default implementation checks
     * {@link org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()}.
     * @param bdHolder the bean definition including bean name and aliases
     * @param descriptor the descriptor for the target method parameter or field
     * @return whether the bean definition qualifies as autowire candidate
     * @see org.springframework.beans.factory.config.BeanDefinition#isAutowireCandidate()
     */
    default boolean isAutowireCandidate(BeanDefinitionHolder bdHolder, DependencyDescriptor descriptor) {
        return bdHolder.getBeanDefinition().isAutowireCandidate();
    }

    /**
     * Determine whether the given descriptor is effectively required.
     * <p>The default implementation checks {@link DependencyDescriptor#isRequired()}.
     * @param descriptor the descriptor for the target method parameter or field
     * @return whether the descriptor is marked as required or possibly indicating
     * non-required status some other way (e.g. through a parameter annotation)
     * @since 5.0
     * @see DependencyDescriptor#isRequired()
     */
    default boolean isRequired(DependencyDescriptor descriptor) {
        return descriptor.isRequired();
    }

    /**
     * Determine whether the given descriptor declares a qualifier beyond the type
     * (typically - but not necessarily - a specific kind of annotation).
     * <p>The default implementation returns {@code false}.
     * @param descriptor the descriptor for the target method parameter or field
     * @return whether the descriptor declares a qualifier, narrowing the candidate
     * status beyond the type match
     * @since 5.1
     * @see org.springframework.beans.factory.annotation.QualifierAnnotationAutowireCandidateResolver#hasQualifier
     */
    default boolean hasQualifier(DependencyDescriptor descriptor) {
        return false;
    }

    /**
     * Determine whether a default value is suggested for the given dependency.
     * <p>The default implementation simply returns {@code null}.
     * @param descriptor the descriptor for the target method parameter or field
     * @return the value suggested (typically an expression String),
     * or {@code null} if none found
     * @since 3.0
     */
    @Nullable
    default Object getSuggestedValue(DependencyDescriptor descriptor) {
        return null;
    }

    /**
     * Build a proxy for lazy resolution of the actual dependency target,
     * if demanded by the injection point.
     * <p>The default implementation simply returns {@code null}.
     * @param descriptor the descriptor for the target method parameter or field
     * @param beanName the name of the bean that contains the injection point
     * @return the lazy resolution proxy for the actual dependency target,
     * or {@code null} if straight resolution is to be performed
     * @since 4.0
     */
    @Nullable
    default Object getLazyResolutionProxyIfNecessary(DependencyDescriptor descriptor, @Nullable String beanName) {
        return null;
    }

}