初始化一個Springboot項目，在主啟動類會有這么一個注解:@SpringBootApplication,自動裝配的秘密全在主啟動類這個注解里面了

點進去一層會發現有三個子注解組成，分別是 @SpringBootConfiguration、@ComponentScan和@EnableAutoConfiguration

接下來分別解釋這三個注解在整個自動裝配過程中的作用

點進去發現它是@Configure，代表當前是一個配置類，意思就是當前這個主啟動類是一個配置類，當然也在Spring容器中，這樣方便啟動的時對其他對象進行管理。

指定掃描哪些Spring注解

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

源碼中指定兩種情況下會被排除在外

@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:用于排除其他同時標記@Configuration和@EnableAutoConfiguration的類

@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()); }

所有的重量全部都加在這個注解上面

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

@AutoConfigurationPackage

自動配置包？指定了默認的包規則

@Import(AutoConfigurationPackages.Registrar.class) //給容器中導入一個組件public @interface AutoConfigurationPackage {}//利用Registrar給容器中導入一系列組件//將指定的一個包下的所有組件導入進來？MainApplication 所在包下。

@Import(AutoConfigurationImportSelector.class)

1、利用getAutoConfigurationEntry(annotationMetadata);給容器中批量導入一些組件2、調用List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes)獲取到所有需要導入到容器中的配置類3、利用工廠加載 Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader)；得到所有的組件4、從META-INF/spring.factories位置來加載一個文件。 默認掃描我們當前系統里面所有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

文件里面寫死了spring-boot一啟動就要給容器中加載的所有配置類

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.h2.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.oauth2.client.servlet.OAuth2ClientAutoConfiguration,org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,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

思考🤔：就這些，說白了就是SpringBoot 在項目啟動的時候封裝了創建對象的方法，無需我們手動配置。

美其名曰自動配置，實則是前人幫我們手動配置好了~

其實SprigBoot有一個條件選擇加載的機制，他并不會把META-INF/spring.factories 目錄下的所有類全部放置到容器中，感興趣的同學可以去詳細看一下，Sprignboot條件加載機制，@Condition系列注解。

以上就是SpringBoot 自動配置原理，翻源碼看一下的詳細內容，更多關于SpringBoot 自動配置的資料請關注好吧啦網其它相關文章！