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本文主要研究一下springboot的启动事件

SpringApplicationEvent

org/springframework/boot/context/event/SpringApplicationEvent.java

public abstract class SpringApplicationEvent extends ApplicationEvent {private final String[] args;public SpringApplicationEvent(SpringApplication application, String[] args) {super(application);this.args = args;}public SpringApplication getSpringApplication() {return (SpringApplication) getSource();}public final String[] getArgs() {return this.args;}}

SpringApplicationEvent继承了ApplicationEvent，它有几个子类分表是ApplicationStartingEvent、ApplicationEnvironmentPreparedEvent、ApplicationContextInitializedEvent、ApplicationPreparedEvent、ApplicationStartedEvent、ApplicationReadyEvent，期间有异常则抛出ApplicationFailedEvent

SpringApplication.run

org/springframework/boot/SpringApplication.java

	public ConfigurableApplicationContext run(String... args) {StopWatch stopWatch = new StopWatch();stopWatch.start();ConfigurableApplicationContext context = null;Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();configureHeadlessProperty();SpringApplicationRunListeners listeners = getRunListeners(args);listeners.starting();try {ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext();exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,new Class[] { ConfigurableApplicationContext.class }, context);prepareContext(context, environment, listeners, applicationArguments, printedBanner);refreshContext(context);afterRefresh(context, applicationArguments);stopWatch.stop();if (this.logStartupInfo) {new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);}listeners.started(context);callRunners(context, applicationArguments);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, listeners);throw new IllegalStateException(ex);}try {listeners.running(context);}catch (Throwable ex) {handleRunFailure(context, ex, exceptionReporters, null);throw new IllegalStateException(ex);}return context;}

SpringApplication的run方法，先触发listeners.starting()，然后执行了prepareEnvironment，之后createApplicationContext，再进行prepareContext和refreshContext，最后触发listeners.started(context)，之后执行callRunners，最后触发listeners.running(context)，如有异常则会执行handleRunFailure

prepareEnvironment

	private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {// Create and configure the environmentConfigurableEnvironment environment = getOrCreateEnvironment();configureEnvironment(environment, applicationArguments.getSourceArgs());ConfigurationPropertySources.attach(environment);listeners.environmentPrepared(environment);bindToSpringApplication(environment);if (!this.isCustomEnvironment) {environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,deduceEnvironmentClass());}ConfigurationPropertySources.attach(environment);return environment;}

prepareEnvironment会触发listeners.environmentPrepared(environment)，即发布ApplicationEnvironmentPreparedEvent

prepareContext

	private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {context.setEnvironment(environment);postProcessApplicationContext(context);applyInitializers(context);listeners.contextPrepared(context);if (this.logStartupInfo) {logStartupInfo(context.getParent() == null);logStartupProfileInfo(context);}// Add boot specific singleton beansConfigurableListableBeanFactory beanFactory = context.getBeanFactory();beanFactory.registerSingleton("springApplicationArguments", applicationArguments);if (printedBanner != null) {beanFactory.registerSingleton("springBootBanner", printedBanner);}if (beanFactory instanceof DefaultListableBeanFactory) {((DefaultListableBeanFactory) beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);}if (this.lazyInitialization) {context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());}// Load the sourcesSet<Object> sources = getAllSources();Assert.notEmpty(sources, "Sources must not be empty");load(context, sources.toArray(new Object[0]));listeners.contextLoaded(context);}

prepareContext会触发listeners.contextPrepared(context)，即发布ApplicationContextInitializedEvent，执行完成之后触发listeners.contextLoaded(context)，即发布ApplicationPreparedEvent

refreshContext

	private void refreshContext(ConfigurableApplicationContext context) {refresh(context);if (this.registerShutdownHook) {try {context.registerShutdownHook();}catch (AccessControlException ex) {// Not allowed in some environments.}}}protected void refresh(ApplicationContext applicationContext) {Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);((AbstractApplicationContext) applicationContext).refresh();}	

refreshContext会执行refresh方法

org/springframework/context/support/AbstractApplicationContext.java

	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();}catch (BeansException ex) {if (logger.isWarnEnabled()) {logger.warn("Exception encountered during context initialization - " +"cancelling refresh attempt: " + ex);}// Destroy already created singletons to avoid dangling resources.destroyBeans();// Reset 'active' flag.cancelRefresh(ex);// Propagate exception to caller.throw ex;}finally {// Reset common introspection caches in Spring's core, since we// might not ever need metadata for singleton beans anymore...resetCommonCaches();}}}

refresh先执行postProcessBeanFactory，比如添加BeanPostProcessors，之后执行invokeBeanFactoryPostProcessors，即执行BeanFactoryPostProcessor的postProcessBeanFactory方法
refresh执行完之后触发listeners.started(context)即发布ApplicationStartedEvent
执行完callRunners之后触发listeners.running(context)即发布ApplicationReadyEvent

handleRunFailure

	private void handleRunFailure(ConfigurableApplicationContext context, Throwable exception,Collection<SpringBootExceptionReporter> exceptionReporters, SpringApplicationRunListeners listeners) {try {try {handleExitCode(context, exception);if (listeners != null) {listeners.failed(context, exception);}}finally {reportFailure(exceptionReporters, exception);if (context != null) {context.close();}}}catch (Exception ex) {logger.warn("Unable to close ApplicationContext", ex);}ReflectionUtils.rethrowRuntimeException(exception);}

触发listeners.failed(context, exception)即发布ApplicationFailedEvent

小结

SpringApplication的run方法，先触发listeners.starting()(ApplicationStartingEvent)，然后执行了prepareEnvironment(ApplicationEnvironmentPreparedEvent)，之后createApplicationContext，再进行prepareContext和refreshContext(ApplicationContextInitializedEvent–>ApplicationPreparedEvent)，最后触发listeners.started(context)(ApplicationStartedEvent)，之后执行callRunners，最后触发listeners.running(context)(ApplicationReadyEvent)，期间有异常会执行handleRunFailure，触发listeners.failed(context, exception)(ApplicationFailedEvent)

其中refresh的时候会执行BeanFactoryPostProcessor的postProcessBeanFactory方法
整体顺序如下：ApplicationStartingEvent --> ApplicationEnvironmentPreparedEvent --> ApplicationContextInitializedEvent --> ApplicationPreparedEvent --> ApplicationStartedEvent --> ApplicationReadyEvent，期间有异常则抛出ApplicationFailedEvent