第三章 SpringBoot自动配置

1. 引导加载自动配置类

@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
		@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication{}

1.1 @SpringBootConfiguration

​ 同@Configuration，代表当前是一个配置类。

1.2 @ComponentScan

​ 指定扫描哪些。

1.3 @EnableAutoConfiguration

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

• @AutoConfigurationPackage

  指定了默认的包规则，导入Application所在包下的组件。

  @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)

  导入所有场景启动器对应的配置类。

  1、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
  

  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 Configure
  org.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
  

  2. 按需开启自动配置项

  虽然所有自动配置启动的时候默认全部加载。xxxxAutoConfiguration按照条件装配规则（@Conditional），最终会按需配置。
  

  3. 修改默认配置

  @Bean
  @ConditionalOnBean(MultipartResolver.class)  //容器中有这个类型组件
  @ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME) //容器中没有这个名字 multipartResolver 的组件
  public MultipartResolver multipartResolver(MultipartResolver resolver) {
      //给@Bean标注的方法传入了对象参数，这个参数的值就会从容器中找。
      //SpringMVC multipartResolver。防止有些用户配置的文件上传解析器不符合规范
      // Detect if the user has created a MultipartResolver but named it incorrectly
      return resolver;
  }
  给容器中加入了文件上传解析器；
  

  SpringBoot默认会在底层配好所有的组件。但是如果用户自己配置了以用户的优先。

  @Bean
  @ConditionalOnMissingBean
  public CharacterEncodingFilter characterEncodingFilter() {
  }
  

  4. 总结

  • SpringBoot先加载所有的自动配置类 xxxxxAutoConfiguration

  • 每个自动配置类按照条件进行生效，默认都会绑定配置文件指定的值。

  • 生效的配置类就会给容器中装配很多组件

  • 只要容器中有这些组件，相当于这些功能就有了

  • 定制化配置

  • • 用户直接自己@Bean替换底层的组件
    • 用户去看这个组件是获取的配置文件什么值就去修改。

  xxxxxAutoConfiguration ---> 组件 ---> xxxxProperties里面拿值 ----> application.properties

  5. 最佳实践

  • 引入场景依赖

  • 查看自动配置了哪些（选做）

  • 自己分析，引入场景对应的自动配置一般都生效了

    • 配置文件中debug=true开启自动配置报告。Negative（不生效）\Positive（生效）

  • 是否需要修改

    • 参照文档修改配置项
    • 自己分析。xxxxProperties绑定了配置文件的哪些。

  • 自定义加入或者替换组件

    • @Bean、@Component

  • 自定义器 XXXXXCustomizer