SpringBoot之自动配置原理
SpringBoot之自动配置原理
配置文件到底能写什么？怎么写？----可以看---- spring.factories
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/2.4.3.RELEASE/reference/html/appendix-application-properties.html#core-properties
分析自动配置原理
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SpringBoot启动的时候加载主配置类，开启了自动配置功能 @EnableAutoConfiguration
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@EnableAutoConfiguration 作用
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利用EnableAutoConfigurationImportSelector给容器中导入一些组件
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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叫做获取候选的配置 ，我们点击继续跟踪configurations = getCandidateConfigurations(annotationMetadata, attributes); 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
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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；
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每一个自动配置类进行自动配置功能；
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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(org.springframework.boot.autoconfigure.http.HttpProperties.Encoding.Type.REQUEST)); filter.setForceResponseEncoding(this.properties.shouldForce(org.springframework.boot.autoconfigure.http.HttpProperties.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！
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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；
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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；
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所有在配置文件中能配置的属性都是在xxxxProperties类中封装着；
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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
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SpringBoot启动会加载大量的自动配置类
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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；
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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）
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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；
@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
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Positive matches:（自动配置类启用的：正匹配）
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Negative matches:（没有启动，没有匹配成功的自动配置类：负匹配）
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Unconditional classes: （没有条件的类）
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【查看输出的日志】
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