SpringBoot 启动过程 SpringApplication.run 这是我参与8月更文挑战的第19天，活动详情查

这是我参与8月更文挑战的第19天，活动详情查看：8月更文挑战

开启日志

logging:
  level:
    org.springframework: trace

启动项目从日志中依次可以看到这么几个主要类

PropertySourcesPropertyResolver

ClassPathBeanDefinitionScanner

DefaultListableBeanFactory

DockerApplication

SpringApplication

ConfigFileApplicationListener

ConfigServletWebServerApplicationContext

SpringFactoriesLoader

PathMatchingResourcePatternResolver

OnClassCondition

OnWebApplicationCondition

OnBeanCondition

ConfigurationClassBeanDefinitionReader

TomcatServletWebServerFactory

AutowiredAnnotationBeanPostProcessor

CommonAnnotationBeanPostProcessor

ThreadPoolTaskExecutor

RequestMappingHandlerMapping

TomcatWebServer

其基本流程

加载配置文件，装载bean对象，初始化请求映射器，启动内嵌的tomcat。

配置文件加载日志

ConfigFileApplicationListener  : Skipped missing config 'file:./config/application.properti
ConfigFileApplicationListener  : Skipped missing config 'file:./config/application.xml' (fi
ConfigFileApplicationListener  : Skipped missing config 'file:./config/application.yml' (fi
ConfigFileApplicationListener  : Skipped missing config 'file:./config/application.yaml' (f
ConfigFileApplicationListener  : Skipped missing config 'file:./application.properties' (fi
ConfigFileApplicationListener  : Skipped missing config 'file:./application.xml' (file:./ap
ConfigFileApplicationListener  : Skipped missing config 'file:./application.yml' (file:./ap
ConfigFileApplicationListener  : Skipped missing config 'file:./application.yaml' (file:./a
ConfigFileApplicationListener  : Skipped missing config classpath:/config/application.prope
ConfigFileApplicationListener  : Skipped missing config classpath:/config/application.xml  
ConfigFileApplicationListener  : Skipped missing config classpath:/config/application.yml  
ConfigFileApplicationListener  : Skipped missing config classpath:/config/application.yaml 
ConfigFileApplicationListener  : Skipped missing config classpath:/application.properties  
ConfigFileApplicationListener  : Skipped missing config classpath:/application.xml         
ConfigFileApplicationListener  : Loaded config file 'file:.../target/classes/application.yml'  (classpath:/application.yml)
ConfigFileApplicationListener  : Skipped missing config classpath:/application.yaml

日志的加载顺序

从日志中可以看出日志的加载顺序

file > classpath
config > 当前目录.
Properties > xml > ym l> yaml

run的过程

SpringApplication.run的过程构建了ApplicationContext

public ConfigurableApplicationContext run(String... args) {
  // 耗时统计
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
		configureHeadlessProperty();
    // application监听
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      // 加载环境变量 配置文件
			ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
			configureIgnoreBeanInfo(environment);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
					new Class[] { ConfigurableApplicationContext.class }, context);
      // 准备上下文
			prepareContext(context, environment, listeners, applicationArguments, printedBanner);
			// 刷新上下文
      refreshContext(context);
			afterRefresh(context, applicationArguments);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
			}
      // 程序已启动
			listeners.started(context);
			callRunners(context, applicationArguments);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, listeners);
			throw new IllegalStateException(ex);
		}

		try {
      // 程序正在运行
			listeners.running(context);
		}
		catch (Throwable ex) {
			handleRunFailure(context, ex, exceptionReporters, null);
			throw new IllegalStateException(ex);
		}
		return context;
	}

AnnotationConfigServletWebServerApplicationContext 继承关系

AbstractApplicationContext (org.springframework.context.support)

|--GenericApplicationContext (org.springframework.context.support)

|--|--GenericWebApplicationContext (org.springframework.web.context.support)

|--|--|--ServletWebServerApplicationContext (org.springframework.boot.web.servlet.context)

|--|--|--|--AnnotationConfigServletWebServerApplicationContext (org.springframework.boot.web.servlet.context)

refreshBean 使用DefaultListableBeanFactory进行加载bean

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// Initialize other special beans in specific context subclasses.
				onRefresh();

				// Check for listener beans and register them.
				registerListeners();

				// Instantiate all remaining (non-lazy-init) singletons.
				finishBeanFactoryInitialization(beanFactory);

				// Last step: publish corresponding event.
				finishRefresh();
			}
			...
			}

ApplicationListener与 ApplicationEvent

ApplicationEvent部分继承关系

ApplicationEvent (org.springframework.context)
|--SpringApplicationEvent (org.springframework.boot.context.event)
|--|--ApplicationEnvironmentPreparedEvent
|--|--ApplicationContextInitializedEvent (org.springframework.boot.context.event)
|--|--|--ApplicationEnvironmentPreparedEvent (org.springframework.boot.context.event)
|--|--|--ApplicationPreparedEvent (org.springframework.boot.context.event)
|--|--|--ApplicationStartedEvent (org.springframework.boot.context.event)
|--|--|--ApplicationReadyEvent (org.springframework.boot.context.event)
|--|--|--ApplicationFailedEvent (org.springframework.boot.context.event)
|--ApplicationContextEvent (org.springframework.context.event)
|--|--ContextClosedEvent (org.springframework.context.event)
|--|--ContextRefreshedEvent (org.springframework.context.event)
|--|--ContextStoppedEvent (org.springframework.context.event)
|--|--ContextStartedEvent (org.springframework.context.event)
|-- ...

SimpleApplicationEventMulticaster 用于管理 ApplicationListener与 ApplicationEvent，这有点像java swing中的事件处理，如鼠标点击发送一个事件，然后有一个listener处理这个事件。

multicastEvent用于触发listener与envent事件，最终调用listener的onApplicationEvent方法。
如 ConfigFileApplicationListener 处理 ApplicationEnvironmentPreparedEvent事件。 LoggingApplicationListener处理 ApplicationEnvironmentPreparedEvent事件。

整个启动过程listener 开始启动==>启动完成==>正在运行

listeners.starting();
...
listeners.started(context);
...
listeners.running(context);

listeners保存了已注册的SpringApplicationRunListener列表，listeners的处理即循环调用每个listener的处理。

SpringApplicationRunListener的实现类EventPublishingRunListener。

Listener通过SimpleApplicationEventMulticaster#multicastEvent广播事件，doInvokeListener调用事件处理，监听listener调用onApplicationEvent进行处理事件。

listeners.started(context) 的事件传播是通过AbstractApplicationContext#publishEvent进行Event加工及关联较早的事件，再通过SimpleApplicationEventMulticaster进行广播事件，同时事件向父类传播。

来看下整个启动过程的监听内容

public interface SpringApplicationRunListener {

 /**
  * 正在启动
  * Called immediately when the run method has first started. Can be used for very
  * early initialization.
  */
 default void starting() {
 }

 /**
  * 环境准备完成
  * Called once the environment has been prepared, but before the
  * {@link ApplicationContext} has been created.
  * @param environment the environment
  */
 default void environmentPrepared(ConfigurableEnvironment environment) {
 }

 /**
  * context准备完成
  * Called once the {@link ApplicationContext} has been created and prepared, but
  * before sources have been loaded.
  * @param context the application context
  */
 default void contextPrepared(ConfigurableApplicationContext context) {
 }

 /**
  * context加载完成
  * Called once the application context has been loaded but before it has been
  * refreshed.
  * @param context the application context
  */
 default void contextLoaded(ConfigurableApplicationContext context) {
 }

 /**
  * 启动完成
  * The context has been refreshed and the application has started but
  * {@link CommandLineRunner CommandLineRunners} and {@link ApplicationRunner
  * ApplicationRunners} have not been called.
  * @param context the application context.
  * @since 2.0.0
  */
 default void started(ConfigurableApplicationContext context) {
 }

 /**
  * 正在运行
  * Called immediately before the run method finishes, when the application context has
  * been refreshed and all {@link CommandLineRunner CommandLineRunners} and
  * {@link ApplicationRunner ApplicationRunners} have been called.
  * @param context the application context.
  * @since 2.0.0
  */
 default void running(ConfigurableApplicationContext context) {
 }

 /**
  * 失败
  * Called when a failure occurs when running the application.
  * @param context the application context or {@code null} if a failure occurred before
  * the context was created
  * @param exception the failure
  * @since 2.0.0
  */
 default void failed(ConfigurableApplicationContext context, Throwable exception) {
 }

}

总结

SpirngApplication 在启动时通过listener处理启动过程的一些事件event。加载上下文过程先获取环境变量配置文件，创建初始context ，prepareContext阶段将context、environment与listener绑定，处理后续的event，refreshContext阶段进行bean加载及postProcessors处理，自动装配加载，条件配置bean的加载，最终生成装配完bean的上下文ApplicationContext，最后发布程序启动完成、正在运行事件，并有listener进行处理，至此程序启动完成。

今天暂且写到这，有空继续研究。