Code of Spring and Spring Boot 16 Apr 2018

基于Spring Boot 2.0.x和Spring 5.0.x

Spring Boot启动流程

1. 检测Spring应用类型(Reactive-Web, Non-Web以及Web-Servlet)
2. 通过spring.factories文件加载并实例化注册的org.springframework.context.ApplicationContextInitializers
3. 通过spring.factories文件加载并实例化注册的org.springframework.context.ApplicationListeners
4. 确定Spring Boot工程的Main Class
5. 通过spring.factories文件加载并实例化注册的org.springframework.boot.SpringApplicationRunListener, 并分发ApplicationStartingEvent事件给ApplicationListeners
6. 根据应用类型创建org.springframework.core.env.ConfigurableEnvironment实例, 分发ApplicationEnvironmentPreparedEvent事件给ApplicationListeners
7. 创建org.springframework.context.ConfigurableApplicationContext实例
8. Apply ApplicationContextInitializers
9. SpringApplicationRunListeners#contextPrepared(空方法)
10. load(annotated main class)
11. 分发ApplicationPreparedEvent事件给ApplicationListeners
12. context.refresh
13. 由ApplicationContext分发ApplicationStartedEvent事件
14. 由ApplicationContext分发分发ApplicationReadyEvent事件
15. 如果应用在启动过程中有错误发生, 则分发ApplicationFailedEvent事件给ApplicationListeners

Spring Boot预置的spring.factories

Spring Boot通过org.springframework.core.io.support.SpringFactoriesLoader#loadFactories(Class clazz, ClassLoader loader)来获取某个类别下的实例

ApplicationContextInitializer

• spring-boot
  • org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer
  • org.springframework.boot.context.ContextIdApplicationContextInitializer
  • org.springframework.boot.context.config.DelegatingApplicationContextInitializer
  • org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer
• • -
• spring-boot-autoconfigure
  • org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer
  • org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
• • -
• 如果引入了spring-boot-devtools, 还包括以下ApplicationContextInitializer
  • org.springframework.boot.devtools.restart.RestartScopeInitializer

ApplicationListener

• spring-boot
  • org.springframework.boot.ClearCachesApplicationListener
  • org.springframework.boot.builder.ParentContextCloserApplicationListener
  • org.springframework.boot.context.FileEncodingApplicationListener
  • org.springframework.boot.context.config.AnsiOutputApplicationListener
  • org.springframework.boot.context.config.ConfigFileApplicationListener
  • org.springframework.boot.context.config.DelegatingApplicationListener
  • org.springframework.boot.context.logging.ClasspathLoggingApplicationListener
  • org.springframework.boot.context.logging.LoggingApplicationListener
  • org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
• • -
• spring-boot-autoconfigure
  • org.springframework.boot.autoconfigure.BackgroundPreinitializer
• • -
• 如果引入了spring-boot-devtools, 还包括以下ApplicationListener
  • org.springframework.boot.devtools.restart.RestartApplicationListener

SpringApplicationRunListener

• org.springframework.boot.context.event.EventPublishingRunListener

Spring Boot启动过程中部分重要的事件以及处理过程

ApplicationStartingEvent

• LoggingApplicationListener: 构建日志系统
• BackgroundPreinitializer: 后台启动一个线程, 用来预先初始化一些服务
• RestartApplicationListener: 初始化Restarter

ApplicationEnvironmentPreparedEvent

• ConfigFileApplicationListener: 载入注册于spring.factories的org.springframework.boot.env.EnvironmentPostProcessors, 主要用于在context.refresh之前自定义应用的Environment, 并且载入注册的org.springframework.boot.env.PropertySourceLoader定义的属性配置, 例如application.yml
• DelegatingApplicationListener: 在本阶段(EnvironmentPrepared)载入注册于context.listener.classes属性下的ApplicationListeners, 并将后续事件分发给他们
• LoggingApplicationListener: 初始化日志系统, 并注册Shutdown Hook
• ConfigFileApplicationListener: 将默认属性优先级将为最低

ApplicationPreparedEvent(contextLoaded)

• LoggingApplicationListener: 将日志系统注册到BeanFactory

ApplicationStartedEvent(contextRefreshed)

ApplicationReadyEvent(main class run)

• BackgroundPreinitializer: 如果预载服务的线程任务没有结束, 阻塞主线程

ApplicationContextInitializer初始化过程

• ConfigurationWarningsApplicationContextInitializer: 对有问题的BeanDefinitionRegistry进行提示
• ContextIdApplicationContextInitializer: 创建一个ContextId, 并将其注册到BeanFactory
• DelegatingApplicationContextInitializer: 初始化其他注册在context.initializer.classes的ApplicationContextInitializer
• ServerPortInfoApplicationContextInitializer: 将自身作为一个ApplicationListener注册到ApplicationContext, 用于监听WebServerInitializedEvent事件
• SharedMetadataReaderFactoryContextInitializer: 创建一个ConfigurationClassPostProcessor(用于处理标注@Configuration的类)和Spring Boot共享的一个MetadataReader, 用于读取类的元信息
• • -
• ConditionEvaluationReportLoggingListener: 注册一个ApplicationListener用于在contextRefreshed的时候打印Auto Configuration的信息
• RestartScopeInitializer: 注册一个RestartScope到BeanFactory

ApplicationContext.refresh