EnableAutoConfiguration注解说明

Posted 2022-02-06 zhujunhuawoaini

/*
 * Copyright 2012-2017 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.boot.autoconfigure;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.web.embedded.tomcat.TomcatServletWebServerFactory;
import org.springframework.boot.web.servlet.server.ServletWebServerFactory;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.core.io.support.SpringFactoriesLoader;

/**
 * Enable auto-configuration of the Spring Application Context, attempting to guess and
 * configure beans that you are likely to need. Auto-configuration classes are usually
 * applied based on your classpath and what beans you have defined. For example, if you
 * have @code tomcat-embedded.jar on your classpath you are likely to want a
 * @link TomcatServletWebServerFactory (unless you have defined your own
 * @link ServletWebServerFactory bean).
 * <p>
 * When using @link SpringBootApplication, the auto-configuration of the context is
 * automatically enabled and adding this annotation has therefore no additional effect.
 * <p>
 * Auto-configuration tries to be as intelligent as possible and will back-away as you
 * define more of your own configuration. You can always manually @link #exclude() any
 * configuration that you never want to apply (use @link #excludeName() if you don‘t
 * have access to them). You can also exclude them via the
 * @code spring.autoconfigure.exclude property. Auto-configuration is always applied
 * after user-defined beans have been registered.
 * <p>
 * The package of the class that is annotated with @code @EnableAutoConfiguration,
 * usually via @code @SpringBootApplication, has specific significance and is often used
 * as a ‘default‘. For example, it will be used when scanning for @code @Entity classes.
 * It is generally recommended that you place @code @EnableAutoConfiguration (if you‘re
 * not using @code @SpringBootApplication) in a root package so that all sub-packages
 * and classes can be searched.
 * <p>
 * Auto-configuration classes are regular Spring @link Configuration beans. They are
 * located using the @link SpringFactoriesLoader mechanism (keyed against this class).
 * Generally auto-configuration beans are @link Conditional @Conditional beans (most
 * often using @link ConditionalOnClass @ConditionalOnClass and
 * @link ConditionalOnMissingBean @ConditionalOnMissingBean annotations).
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @see ConditionalOnBean
 * @see ConditionalOnMissingBean
 * @see ConditionalOnClass
 * @see AutoConfigureAfter
 * @see SpringBootApplication
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration 

    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";

    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    Class<?>[] exclude() default ;

    /**
     * Exclude specific auto-configuration class names such that they will never be
     * applied.
     * @return the class names to exclude
     * @since 1.3.0
     */
    String[] excludeName() default ;

Spring Boot 自动装配机制的核心是 @EnableAutoConfiguration、@Conditional*、SpringFactoriesLoader