SpringBoot自动配置的原理分析

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初始化一个Springboot项目，在主启动类会有这么一个注解:@SpringBootApplication,自动装配的秘密全在主启动类这个注解里面了

点进去一层会发现有三个子注解组成，分别是 @SpringBootConfiguration、@ComponentScan和@EnableAutoConfiguration

接下来分别解释这三个注解在整个自动装配过程中的作用

1、@SpringBootConfiguration

点进去发现它是@Configure，代表当前是一个配置类，意思就是当前这个主启动类是一个配置类，当然也在Spring容器中，这样方便启动的时对其他对象进行管理。

2、@ComponentScan

指定扫描哪些Spring注解

@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

源码中指定两种情况下会被排除在外

@Override    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)            throws IOException {        //         if (this.beanFactory instanceof ListableBeanFactory && getClass() == TypeExcludeFilter.class) {            for (TypeExcludeFilter delegate : getDelegates()) {                if (delegate.match(metadataReader, metadataReaderFactory)) {                    return true;                }            }        }        return false;    }

AutoConfigurationExcludeFilter:用于排除其他同时标记@Configuration和@EnableAutoConfiguration的类

@Override    public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory)            throws IOException {        return isConfiguration(metadataReader) && isAutoConfiguration(metadataReader);    }    private boolean isConfiguration(MetadataReader metadataReader) {        return metadataReader.getAnnotationMetadata().isAnnotated(Configuration.class.getName());    }    private boolean isAutoConfiguration(MetadataReader metadataReader) {        return getAutoConfigurations().contains(metadataReader.getClaSSMetadata().getClassName());    }

3、@EnableAutoConfiguration

所有的重量全部都加在这个注解上面

@AutoConfigurationPackage@Import(AutoConfigurationImportSelector.class)public @interface EnableAutoConfiguration {}

@AutoConfigurationPackage

自动配置包？指定了默认的包规则

@Import(AutoConfigurationPackages.ReGIStrar.class)  //给容器中导入一个组件public @interface AutoConfigurationPackage {}//利用Registrar给容器中导入一系列组件//将指定的一个包下的所有组件导入进来？MainApplication 所在包下。

@Import(AutoConfigurationImportSelector.class)

利用getAutoConfigurationEntry(annotationMetadata);给容器中批量导入一些组件
2、调用List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes)获取到所有需要导入到容器中的配置类
3、利用工厂加载 Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader)；得到所有的组件
4、从META-INF/spring.factories位置来加载一个文件。
 默认扫描我们当前系统里面所有META-INF/spring.factories位置的文件
    spring-boot-autoconfigure-2.3.4.RELEASE.jar包里面也有META-INF/spring.factories

文件里面写死了spring-boot一启动就要给容器中加载的所有配置类

spring-boot-autoconfigure-2.3.4.RELEASE.jar/META-INF/spring.factories# Auto Configureorg.springframework.boot.autoconfigure.EnableAutoConfiguration=\org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\org.springframework.boot.autoconfigure.aMQp.RabbitAutoConfiguration,\org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\org.springframework.boot.autoconfigure.context.LifecycleAutoConfiguration,\org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\org.springframework.boot.autoconfigure.coucHBase.CouchbaseAutoConfiguration,\org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRestClientAutoConfiguration,\org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.monGo.MongoDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.r2dbc.R2dbcDataAutoConfiguration,\org.springframework.boot.autoconfigure.data.r2dbc.R2dbcRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.r2dbc.R2dbcTransactionManagerAutoConfiguration,\org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\org.springframework.boot.autoconfigure.data.rest.RepositoryRestmvcAutoConfiguration,\org.springframework.boot.autoconfigure.data.WEB.SpringDataWebAutoConfiguration,\org.springframework.boot.autoconfigure.elasticsearch.ElasticsearchRestClientAutoConfiguration,\org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\org.springframework.boot.autoconfigure.h3.H2ConsoleAutoConfiguration,\org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\org.springframework.boot.autoconfigure.Http.HttpMessageConvertersAutoConfiguration,\org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\org.springframework.boot.autoconfigure.JSONb.jsonbAutoConfiguration,\org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\org.springframework.boot.autoconfigure.availability.ApplicationAvailabilityAutoConfiguration,\org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\org.springframework.boot.autoconfigure.ORM.jpa.HibernateJpaAutoConfiguration,\org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\org.springframework.boot.autoconfigure.r2dbc.R2dbcAutoConfiguration,\org.springframework.boot.autoconfigure.rSocket.RSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth3.client.servlet.OAuth3ClientAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth3.client.reactive.ReactiveOAuth3ClientAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth3.resource.servlet.OAuth3ResourceServerAutoConfiguration,\org.springframework.boot.autoconfigure.security.oauth3.resource.reactive.ReactiveOAuth3ResourceServerAutoConfiguration,\org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

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