spring-ImportSelector接口原理

ImportSelector接口源码

package org.springframework.context.annotation;

import org.springframework.core.type.AnnotationMetadata;

/**
 * Interface to be implemented by types that determine which @{@link Configuration}
 * class(es) should be imported based on a given selection criteria, usually one or
 * more annotation attributes.
 *
 * <p>An {@link ImportSelector} may implement any of the following
 * {@link org.springframework.beans.factory.Aware Aware} interfaces,
 * and their respective methods will be called prior to {@link #selectImports}:
 * <ul>
 * <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
 * <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}</li>
 * <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}</li>
 * <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}</li>
 * </ul>
 *
 * <p>{@code ImportSelector} implementations are usually processed in the same way
 * as regular {@code @Import} annotations, however, it is also possible to defer
 * selection of imports until all {@code @Configuration} classes have been processed
 * (see {@link DeferredImportSelector} for details).
 *
 * @author Chris Beams
 * @since 3.1
 * @see DeferredImportSelector
 * @see Import
 * @see ImportBeanDefinitionRegistrar
 * @see Configuration
 */
public interface ImportSelector {

    /**
     * Select and return the names of which class(es) should be imported based on
     * the {@link AnnotationMetadata} of the importing @{@link Configuration} class.
     */
    String[] selectImports(AnnotationMetadata importingClassMetadata);

}

主要作用：

收集需要导入的配置类。如果配置类也实现了Aware接口，先执行Aware的方法

DeferredImportSelector接口源码解析

/*
 * 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.context.annotation;

import java.util.Objects;

import org.springframework.core.type.AnnotationMetadata;
import org.springframework.lang.Nullable;

/**
 * A variation of {@link ImportSelector} that runs after all {@code @Configuration} beans
 * have been processed. This type of selector can be particularly useful when the selected
 * imports are {@code @Conditional}.
 *
 * <p>Implementations can also extend the {@link org.springframework.core.Ordered}
 * interface or use the {@link org.springframework.core.annotation.Order} annotation to
 * indicate a precedence against other {@link DeferredImportSelector}s.
 *
 * <p>Implementations may also provide an {@link #getImportGroup() import group} which
 * can provide additional sorting and filtering logic across different selectors.
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @since 4.0
 */
public interface DeferredImportSelector extends ImportSelector {

    /**
     * Return a specific import group.
     * <p>The default implementations return {@code null} for no grouping required.
     * @return the import group class, or {@code null} if none
     * @since 5.0
     */
    @Nullable
    default Class<? extends Group> getImportGroup() {
        return null;
    }


    /**
     * Interface used to group results from different import selectors.
     */
    interface Group {

        /**
         * Process the {@link AnnotationMetadata} of the importing @{@link Configuration}
         * class using the specified {@link DeferredImportSelector}.
         */
        void process(AnnotationMetadata metadata, DeferredImportSelector selector);

        /**
         * Return the {@link Entry entries} of which class(es) should be imported
         * for this group.
         */
        Iterable<Entry> selectImports();


        /**
         * An entry that holds the {@link AnnotationMetadata} of the importing
         * {@link Configuration} class and the class name to import.
         */
        class Entry {

            private final AnnotationMetadata metadata;

            private final String importClassName;

            public Entry(AnnotationMetadata metadata, String importClassName) {
                this.metadata = metadata;
                this.importClassName = importClassName;
            }

            /**
             * Return the {@link AnnotationMetadata} of the importing
             * {@link Configuration} class.
             */
            public AnnotationMetadata getMetadata() {
                return this.metadata;
            }

            /**
             * Return the fully qualified name of the class to import.
             */
            public String getImportClassName() {
                return this.importClassName;
            }

            @Override
            public boolean equals(Object other) {
                if (this == other) {
                    return true;
                }
                if (other == null || getClass() != other.getClass()) {
                    return false;
                }
                Entry entry = (Entry) other;
                return (Objects.equals(this.metadata, entry.metadata) &&
                        Objects.equals(this.importClassName, entry.importClassName));
            }

            @Override
            public int hashCode() {
                return Objects.hash(this.metadata, this.importClassName);
            }
        }
    }

}