SpringBoot自动配置原理之哪里不会点哪里

自动配置原理

配置文件到底能写什么？怎么写？----联系---- spring.factories
下面就我们就一起探究源码，哪里不会点哪里！

SpringBoot官方文档中有大量的配置，我们无法全部记住,官网：https://docs.spring.io/spring-boot/docs/2.3.4.RELEASE/reference/html/appendix-application-properties.html#core-properties

Core properties

Key	Default Value	Description
debug	false	Enable debug logs.
info.*		Arbitrary properties to add to the info endpoint.
logging.config		Location of the logging configuration file. For instance, classpath:logback.xml for Logback.
logging.exception-conversion-word	%wEx	Conversion word used when logging exceptions.
logging.file.clean-history-on-start	false	Whether to clean the archive log files on startup. Only supported with the default logback setup.
logging.file.max-history	7.0	Maximum number of days archive log files are kept. Only supported with the default logback setup.
logging.file.max-size	10MB	Maximum log file size. Only supported with the default logback setup.
logging.file.name		Log file name (for instance, myapp.log). Names can be an exact location or relative to the current directory.
logging.file.path		Location of the log file. For instance, /var/log.
logging.file.total-size-cap	0B	Total size of log backups to be kept. Only supported with the default logback setup.
logging.group.*		Log groups to quickly change multiple loggers at the same time. For instance, logging.group.db=org.hibernate,org.springframework.jdbc.

分析自动配置原理

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,他返回了一个autoConfigurationEnty,来自this.getAutoConfigurationEntry(autoConfigurationMetadata,annotationMetadata);这个方法我们继续来跟踪：

   • 这个方法有一个值：List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);叫做获取候选的配置 ，我们点击继续跟踪

     • 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

   • 在类路径下,META-INF/spring.factories里面配置的所有EnableAutoConfiguration的值加入到容器中：

     # 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.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
     
     # 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.r2dbc.ConnectionFactoryBeanCreationFailureAnalyzer,\
     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；

4. 我们以HttpEncodingAutoConfiguration（Http编码自动配置） 为例解释自动配置原理；

   //表示这是一个配置类，和以前编写的配置文件一样，也可以给容器中添加组件；
   @Configuration 
      
   //启动指定类的ConfigurationProperties功能；
     //进入这个HttpProperties查看，将配置文件中对应的值和HttpProperties绑定起来；
     //并把HttpProperties加入到ioc容器中
   @EnableConfigurationProperties({
         
         HttpProperties.class}) 
      
   //Spring底层@Conditional注解
     //根据不同的条件判断，如果满足指定的条件，整个配置类里面的配置就会生效；
     //这里的意思就是判断当前应用是否是web应用，如果是，当前配置类生效
   @ConditionalOnWebApplication(
       type = Type.SERVLET
   )
      
   //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；
   @ConditionalOnClass({
         
         CharacterEncodingFilter.class})
      
   //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
     //即使我们配置文件中不配置pring.http.encoding.enabled=true，也是默认生效的；
   @ConditionalOnProperty(
       prefix = "spring.http.encoding",
       value = {
         
         "enabled"},
       matchIfMissing = true
   )
      
   public class HttpEncodingAutoConfiguration {
         
         
       //他已经和SpringBoot的配置文件映射了
       private final Encoding properties;
       //只有一个有参构造器的情况下，参数的值就会从容器中拿
       public HttpEncodingAutoConfiguration(HttpProperties properties) {
         
         
           this.properties = properties.getEncoding();
       }
      
       //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
       @Bean
       @ConditionalOnMissingBean //判断容器没有这个组件？
       public CharacterEncodingFilter characterEncodingFilter() {
         
         
   		CharacterEncodingFilter filter = new OrderedCharacterEncodingFilter();
   		filter.setEncoding(this.properties.getCharset().name());
   		filter.setForceRequestEncoding(this.properties.shouldForce(Encoding.Type.REQUEST));
   		filter.setForceResponseEncoding(this.properties.shouldForce(Encoding.Type.RESPONSE));
   		return filter;
   	}
       //。。。。。。。
   }
   

一句话总结 ：根据当前不同的条件判断，决定这个配置类是否生效！

• 一但这个配置类生效；这个配置类就会给容器中添加各种组件；

• 这些组件的属性是从对应的properties类中获取的，这些类里面的每一个属性又是和配置文件绑定的；

• 所有在配置文件中能配置的属性都是在xxxxProperties类中封装着；

• 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

  //从配置文件中获取指定的值和bean的属性进行绑定
  @ConfigurationProperties(prefix = "spring.http") 
  public class HttpProperties {
        
        
      // .....
  }
  

我们去配置文件里面试试前缀，看提示！

这就是自动装配的原理！

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在SpringBoot默认写好的自动配置类当中；

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存在在其中，我们就不需要再手动配置了）

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。我们只需要在配置文件中指定这些属性的值即可；

   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； 对应springboot配置，xxx.yaml

@Conditional

了解完自动装配的原理后，我们来关注一个细节问题，自动配置类必须在一定的条件下才能生效；

@Conditional派生注解（Spring注解版原生的@Conditional作用）

作用：必须是@Conditional指定的条件成立，才给容器中添加组件，配置配里面的所有内容才生效；

@Conditional扩展注解	作用(判断是否满足当前指定条件)
@ConditionalOnJava	系统的java版本是否符合要求
@ConditionalOnJava	容器中存在指定Bean ;
@ConditionalOnMissingBean	容器中不存在指定Bean ;
@ConditionalOnExpression	满足SpEL表达式指定
@ConditionalOnClass	系统中有指定的类
@ConditionalOnMissingClass	系统中没有指定的类
@ConditionalOnSingleCandidate	容器中只有一个指定的Bean ,或者这个Bean是首选Bean
@ConditionalOnProperty	系统中指定的属性是否有指定的值
@ConditionalOnResource	类路径下是否存在指定资源文件
@ConditionalOnWebApplication	当前是web环境
@ConditionalOnNotWebApplication	当前不是web环境
@ConditionalOnJndi	JNDI存在指定项

那么多的自动配置类，必须在一定的条件下才能生效；也就是说，我们加载了这么多的配置类，但不是所有的都生效了。

自动配置类是否生效

我们可以在application.properties通过启用 debug=true属性；

在控制台打印自动配置报告，这样我们就可以很方便的知道哪些自动配置类生效；

#开启springboot的调试类
debug=true 

• Positive matches:（自动配置类启用的：正匹配）

• Negative matches:（没有启动，没有匹配成功的自动配置类：负匹配）

• Unconditional classes: （没有条件的类）

• 【演示：查看输出的日志】