SpringBoot的简要总结

简要概述
我们知道SpringBoot是简化了我们的配置,那它是怎么做到的呢?

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class))
public @interface SpringBootApplication {
    
        ...
}

注意到了这里使用@SpringBootApplication注解
继续找到@EnableAutoConfiguration源码：

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
    Class[] exclude() default {};
    String[] excludeName() default {};
}

@Import(EnableAutoConfigurationImportSelector.class)导入一个组件

@AutoConfigurationPackage:存储自动配置类的包通过

/**
*返回自动配置类的名字
*/
protected List getCandidateConfigurations(AnnotationMetadata metadata,
        AnnotationAttributes attributes) {
    List configurations = SpringFactoriesLoader.loadFactoryNames(
            getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
    Assert.notEmpty(configurations,
            "No auto configuration classes found in META-INF/spring.factories. If you "
                    + "are using a custom packaging, make sure that file is correct.");
    return configurations;
}

自动配置类位于 META-INF/spring.factories文件中

---

在我们连接spring是怎么识别出import注解并且把组件注册进去的时候先来了解下BeanFactoryPostProcessor的实现类BeanDefinitionRegistryPostProcessor

而BeanDefinitionRegistryPostProcessor的实现类就是ConfigurationClassPostProcessor；
负责解析处理所有@Configuration标签类，并将Bean定义注册到BeanFactory中。

ConfigurationClassPostProcessor通过ConfigurationClassParser进行实际解析操作。

ConfigurationClassParser将会进行如下解析处理：

处理嵌套的MemberClass

处理@PropertySource标签，用来解析属性文件并设置到Environment中。

处理@ComponentScan标签，扫描package下的所有Class并进行迭代解析。

处理@Import标签。

处理@ImportResource标签。

处理@Bean标签。

处理所有继承的Interface上的@Bean标签。

处理SuperClass。

处理标签中的DeferredImport。
等

---

代码调用链如下

org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors
  ->org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors()
   ->org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors
    ->org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions
     ->org.springframework.context.annotation.ConfigurationClassParser.parse()
      ->org.springframework.context.annotation.ConfigurationClassParser.doProcessConfigurationClass

@Conditional注解
只有满足条件才加载

几个子类如下

条件相关注解.png

---

SpringFactoriesLoader

它扩展了java原生的SPI机制,会从META-INF/spring.factories中查找类,然后根据条件注解,再使用EnableAutoConfigurationImportSelector导入满足条件的类到容器中

---

小结

SpringBoot的核心总结如下
1.@Conditional注解,只有满足条件才加载
2.@Import注解用于根据条件导入配置类
3.SpringFactoriesLoader,从文件中加载默认的配置类

---

Spring Boot启动流程
Spring Boot应用的整个启动流程都封装在SpringApplication.run方法中，其整个流程真的是太长太长了，但本质上就是在Spring容器启动的基础上做了大量的扩展，按照这个思路来看看源码：

publicConfigurableApplicationContextrun(String...args){
    StopWatch stopWatch=newStopWatch();
    stopWatch.start();
   ConfigurableApplicationContext context=null;
   FailureAnalyzers analyzers=null;
   configureHeadlessProperty();// 
  ①SpringApplicationRunListenerslisteners=getRunListeners(args);
  listeners.starting();
try{
    ②ApplicationArguments applicationArguments=newDefaultApplicationArguments(args);
ConfigurableEnvironment environment=prepareEnvironment(listeners,applicationArguments);// 
    ③Banner printedBanner=printBanner(environment);// 
    ④context=createApplicationContext();// 
    ⑤analyzers=newFailureAnalyzers(context);// 
 ⑥prepareContext(context,environment,listeners,applicationArguments,printedBanner);// 
    ⑦ refreshContext(context);// 
    ⑧afterRefresh(context,applicationArguments);// 
    ⑨listeners.finished(context,null);
    stopWatch.stop();
    returncontext;
}catch(Throwableex){
    handleRunFailure(context,listeners,analyzers,ex);
    thrownewIllegalStateException(ex);
}
}

① 通过SpringFactoriesLoader查找并加载所有的 SpringApplicationRunListeners，通过调用starting()方法通知所有的SpringApplicationRunListeners：应用开始启动了。SpringApplicationRunListeners其本质上就是一个事件发布者，它在SpringBoot应用启动的不同时间点发布不同应用事件类型(ApplicationEvent)，如果有哪些事件监听者(ApplicationListener)对这些事件感兴趣，则可以接收并且处理。还记得初始化流程中，SpringApplication加载了一系列ApplicationListener吗？这个启动流程中没有发现有发布事件的代码，其实都已经在SpringApplicationRunListeners这儿实现了。

org.springframework.boot.SpringApplication.run()    
    ->org.springframework.boot.SpringApplication.initialize(Object[])
      ->org.springframework.core.io.support.SpringFactoriesLoader.loadFactoryNames(Class, ClassLoader)   
      从META-INF/spring.factories中依次加载ApplicationContextInitializer ApplicationListener
    ->org.springframework.boot.SpringApplication.run(Object, String...)
      ->org.springframework.boot.SpringApplication.refreshContext()
       ->org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh()
         ->org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors()   执行BeanFactory的前后拦截器 ConfigurationClassPostProcessor 用于执行自动化配置的
          ->org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors()
           ->org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanDefinitionRegistryPostProcessors()
            ->org.springframework.context.annotation.ConfigurationClassPostProcessor.processConfigBeanDefinitions()
             ->org.springframework.context.annotation.ConfigurationClassParser.processDeferredImportSelectors()    我们的自定义组件是通过@Import注解在这里导入的
              ->org.springframework.boot.autoconfigure.AutoConfigurationImportSelector.selectImports()
               ->org.springframework.boot.autoconfigure.AutoConfigurationImportSelector.getCandidateConfigurations()  这个就是众多的自动化配置类
                ->org.springframework.core.io.support.SpringFactoriesLoader.loadFactoryNames(Class, ClassLoader)  最终调用到这里,即Java的SPI机制  会去加载META-INF/spring.factories下的实现类

SpringBoot为我们导入的自动配置的类

[org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration, 
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration, 
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration, 
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration, 
org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration, 
org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration, 
org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration, 
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration, 
org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration, 
org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration, 
org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration, 
org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration, 
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration, 
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration, 
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration, 
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration, 
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration, 
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration, 
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration, 
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration, 
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration, 
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration, 
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration, 
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration, 
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration, 
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration, 
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration, 
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.ldap.embedded.EmbeddedLdapAutoConfiguration, 
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration, 
org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration, 
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration, 
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration, 
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration, 
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration, 
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration, 
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration, 
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration, 
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration, 
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration, 
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration, 
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration, 
org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration, 
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration, 
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration, 
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration, 
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration, 
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration, 
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration, 
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration, 
org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration, 
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration, 
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration, 
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration, 
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration, 
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration, 
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration, 
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration, 
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration, 
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration, 
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration, 
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration, 
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration, 
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration, 
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration, 
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration, 
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration, 
org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration, 
org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration, 
org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration, 
org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration, 
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration, 
org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration, 
org.springframework.boot.autoconfigure.mobile.DeviceResolverAutoConfiguration, 
org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration, 
org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration, 
org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration, 
org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration, 
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration, 
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration, 
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration, 
org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration, 
org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration, 
org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration, 
org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration, 
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration, 
org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration]

还比较多,后面慢慢补