SpringBoot 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的作用：

• 　　利用AutoConfigurationImportSelector给容器中导入一些组件；
• 　　可以参考selectimports()方法的内容；

• List<String> configurations = this.getCandidateConfigurations(annotationMetadata, attributes);获取候选配置

  

  SpringFactoriesLoader.loadFactoryNames();
  扫描所有jar包类路径下 META-INF/spring.factories;
  把扫描到的文件内容包装成properties对象;

  

   

   

  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，如下：
  
  # Initializers
  org.springframework.context.ApplicationContextInitializer=\
  org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
  org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
  
  # Application Listeners
  org.springframework.context.ApplicationListener=\
  org.springframework.boot.autoconfigure.BackgroundPreinitializer
  
  # Auto Configuration Import Listeners
  org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\
  org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener
  
  # Auto Configuration Import Filters
  org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\
  org.springframework.boot.autoconfigure.condition.OnBeanCondition,\
  org.springframework.boot.autoconfigure.condition.OnClassCondition,\
  org.springframework.boot.autoconfigure.condition.OnWebApplicationCondition
  
  # 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.CloudServiceConnectorsAutoConfiguration,\
  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.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.ElasticsearchAutoConfiguration,\
  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.ReactiveRestClientAutoConfiguration,\
  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.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.jest.JestAutoConfiguration,\
  org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\
  org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
  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.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.groovy.template.GroovyTemplateAutoConfiguration,\
  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.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.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
  
  # Failure analyzers
  org.springframework.boot.diagnostics.FailureAnalyzer=\
  org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\
  org.springframework.boot.autoconfigure.flyway.FlywayMigrationScriptMissingFailureAnalyzer,\
  org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\
  org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer,\
  org.springframework.boot.autoconfigure.session.NonUniqueSessionRepositoryFailureAnalyzer
  
  # Template availability providers
  org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\
  org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\
  org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\
  org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\
  org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\
  org.springframework.boot.autoconfigure.web.servlet.JspTemplateAvailabilityProvider

  每一个 xxxAutoConfiguration类都是容器的一个组件，都是加入到容器中；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；

4. 以HttpEncodingAutoConfiguration为例解释自动配置：

@Configuration(proxyBeanMethods = false)　　//标识这是一个配置类，可以给容器添加组件
@EnableConfigurationProperties(HttpProperties.class)　　//启动指定类的ConfigurationProperties功能；
将配置文件中对应的值和HttpEncodingProperties绑定起来;并把HttpEncodingProperties加入到ioc容器中
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)　　//Spring底层@Conditional注解，
根据不同的条件，如果满足指定的条件，整个配置类里面的配置就会生效；这里是判断当前应用是否为web应用，如果是，则当前配置类生效

@ConditionalOnClass(CharacterEncodingFilter.class)　　//判断当前项目有没有这个类，
CharacterEncodingFilter：SpringMVC中进行乱码解决的过滤器
@ConditionalOnProperty(prefix = "spring.http.encoding", value = "enabled", matchIfMissing = true)　　//判断
配置文件中是否存在某个配置 spring.http.encoding.enabled;如果不存在，判断也是成立的

public class HttpEncodingAutoConfiguration {

    private final HttpProperties.Encoding properties;
　　 //只有一个有参构造器，参数的值会默认从容器中拿
    public HttpEncodingAutoConfiguration(HttpProperties properties) {
        this.properties = properties.getEncoding();
    }

    @Bean　　//给容器中添加一个组件，这个组件的某些值需要从properties中获取
    @ConditionalOnMissingBean
    public CharacterEncodingFilter characterEncodingFilter() {
        CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
        filter.setEncoding(this.properties.getCharset().name());
        filter.setForceRequestEncoding(this.properties.shouldForce(Type.REQUEST));
        filter.setForceResponseEncoding(this.properties.shouldForce(Type.RESPONSE));
        return filter;
    }