(转)入门SpringBoot-自动配置原理（三）

1、自动配置原理：

1）、SpringBoot启动的时候加载主配置类，开启了自动配置功能 ==@EnableAutoConfiguration==

2）、@EnableAutoConfiguration 作用：

• 利用EnableAutoConfigurationImportSelector给容器中导入一些组件？

• 可以查看selectImports()方法的内容；

• List configurations = getCandidateConfigurations(annotationMetadata, attributes);获取候选的配配置

• SpringFactoriesLoader.loadFactoryNames()
  扫描所有jar包类路径下  META-INF/spring.factories
  把扫描到的这些文件的内容包装成properties对象
  从properties中获取到EnableAutoConfiguration.class类（类名）对应的值，然后把他们添加在容器中

  ==将 类路径下 META-INF/spring.factories 里面配置的所有EnableAutoConfiguration的值加入到了容器中；==

• # 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.cloud.CloudAutoConfiguration,\
  org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
  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.CassandraRepositoriesAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
  org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
  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.redis.RedisAutoConfiguration,\
  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.jest.JestAutoConfiguration,\
  org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
  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.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.flyway.FlywayAutoConfiguration,\
  org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
  org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
  org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
  org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
  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.mobile.DeviceResolverAutoConfiguration,\
  org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\
  org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\
  org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
  org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
  org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
  org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
  org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\
  org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\
  org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\
  org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\
  org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\
  org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
  org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
  org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\
  org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\
  org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\
  org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\
  org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
  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.DispatcherServletAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\
  org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\
  org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\
  org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\
  org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration

  每一个这样的 xxxAutoConfiguration类都是容器中的一个组件，都加入到容器中；用他们来做自动配置；

  3）、每一个自动配置类进行自动配置功能；

• 所有在配置文件中能配置的属性都是在xxxxProperties类中封装者‘；配置文件能配置什么就可以参照某个功能对应的这个属性类

• 精髓：

  ​ 1）、SpringBoot启动会加载大量的自动配置类

  ​ 2）、我们看我们需要的功能有没有SpringBoot默认写好的自动配置类；

  ​ 3）、我们再来看这个自动配置类中到底配置了哪些组件；（只要我们要用的组件有，我们就不需要再来配置了）

  ​ 4）、给容器中自动配置类添加组件的时候，会从properties类中获取某些属性。我们就可以在配置文件中指定这些属性的值；

  xxxxAutoConfigurartion：自动配置类；

  给容器中添加组件

  xxxxProperties:封装配置文件中相关属性；