Springboot事件和bean生命周期执行机制实例详解

目录

• @PostConstruct执行机制
• ContextRefreshedEvent事件机制
• ApplicationStartedEvent事件机制
• 总结
• 细节问题
• 原因

@PostConstruct执行机制

进入SpringApplication#run(java.lang.String…)

public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	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();
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
		//这里进入就会执行经典的refresh方法进行容器创建工作
		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, listeners);
		throw new IllegalStateException(ex);
	}

	try {
		listeners.running(context);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, null);
		throw new IllegalStateException(ex);
	}
	return context;
}

进入AbstractApplicationContext#refresh

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();

			// 在这里将非懒加载的bean进行创建
			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();
		}
	}
}

进入AbstractApplicationContext#finishBeanFactoryInitialization

AbstractApplicationContext#finishBeanFactoryInitialization

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
	// Initialize conversion service for this context.
	if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
			beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
		beanFactory.setConversionService(
				beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
	}

	// Register a default embedded value resolver if no BeanFactoryPostProcessor
	// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
	// at this point, primarily for resolution in annotation attribute values.
	if (!beanFactory.hasEmbeddedValueResolver()) {
		beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
	}

	// Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
	String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
	for (String weaverAwareName : weaverAwareNames) {
		getBean(weaverAwareName);
	}

	// Stop using the temporary ClassLoader for type matching.
	beanFactory.setTempClassLoader(null);

	// Allow for caching all bean definition metadata, not expecting further changes.
	beanFactory.freezeConfiguration();

	// 将非单例的对象进行真正的创建
	beanFactory.preInstantiateSingletons();
}

在beanFactory.preInstantiateSingletons()中就是循环的创建将非单例的对象，此方法会一直调用到AbstractAutowireCapableBeanFactory#doCreateBean

AbstractAutowireCapableBeanFactory#doCreateBean

protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
		throws BeanCreationException {

	// Instantiate the bean.
	BeanWrapper instanceWrapper = null;
	if (mbd.isSingleton()) {
		instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
	}
	//真正的创建对象
	if (instanceWrapper == null) {
		instanceWrapper = createBeanInstance(beanName, mbd, args);
	}
	Object bean = instanceWrapper.getWrappedInstance();
	Class<?> beanType = instanceWrapper.getWrappedClass();
	if (beanType != NullBean.class) {
		mbd.resolvedTargetType = beanType;
	}

	// Allow post-processors to modify the merged bean definition.
	synchronized (mbd.postProcessingLock) {
		if (!mbd.postProcessed) {
			try {
				applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
			}
			catch (Throwable ex) {
				throw new BeanCreationException(mbd.getResourceDescription(), beanName,
						"Post-processing of merged bean definition failed", ex);
			}
			mbd.postProcessed = true;
		}
	}

	// Eagerly cache singletons to be able to resolve circular references
	// even when triggered by lifecycle interfaces like BeanFactoryAware.
	boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
			isSingletonCurrentlyInCreation(beanName));
	if (earlySingletonExposure) {
		if (logger.isTraceEnabled()) {
			logger.trace("Eagerly caching bean '" + beanName +
					"' to allow for resolving potential circular references");
		}
		addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
	}

	// Initialize the bean instance.
	Object exposedObject = bean;
	try {
		populateBean(beanName, mbd, instanceWrapper);
		//生命周期方法的执行 @PostConstruct就是在此执行的
		exposedObject = initializeBean(beanName, exposedObject, mbd);
	}
	catch (Throwable ex) {
		if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
			throw (BeanCreationException) ex;
		}
		else {
			throw new BeanCreationException(
					mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
		}
	}

	if (earlySingletonExposure) {
		Object earlySingletonReference = getSingleton(beanName, false);
		if (earlySingletonReference != null) {
			if (exposedObject == bean) {
				exposedObject = earlySingletonReference;
			}
			else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
				String[] dependentBeans = getDependentBeans(beanName);
				Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
				for (String dependentBean : dependentBeans) {
					if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
						actualDependentBeans.add(dependentBean);
					}
				}
				if (!actualDependentBeans.isEmpty()) {
					throw new BeanCurrentlyInCreationException(beanName,
							"Bean with name '" + beanName + "' has been injected into other beans [" +
							StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
							"] in its raw version as part of a circular reference, but has eventually been " +
							"wrapped. This means that said other beans do not use the final version of the " +
							"bean. This is often the result of over-eager type matching - consider using " +
							"'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
				}
			}
		}
	}

	// Register bean as disposable.
	try {
		registerDisposableBeanIfNecessary(beanName, bean, mbd);
	}
	catch (BeanDefinitionValidationException ex) {
		throw new BeanCreationException(
				mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
	}

	return exposedObject;
}

AbstractAutowireCapableBeanFactory#initializeBean其中的执行之一就是@PostConstruct

AbstractAutowireCapableBeanFactory#initializeBean

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
	if (System.getSecurityManager() != null) {
		AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
			invokeAwareMethods(beanName, bean);
			return null;
		}, getAccessControlContext());
	}
	else {
		invokeAwareMethods(beanName, bean);
	}

	Object wrappedBean = bean;
	if (mbd == null || !mbd.isSynthetic()) {
		//循环执行PostProcessors后置处理器的postProcessBeforeInitialization方法，@PostConstruct就是在这里执行的
		wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
	}

	try {
		invokeInitMethods(beanName, wrappedBean, mbd);
	}
	catch (Throwable ex) {
		throw new BeanCreationException(
				(mbd != null ? mbd.getResourceDescription() : null),
				beanName, "Invocation of init method failed", ex);
	}
	if (mbd == null || !mbd.isSynthetic()) {
		wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
	}

	return wrappedBean;
}

AbstractAutowireCapableBeanFactory#applyBeanPostProcessorsBeforeInitialization

public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
		throws BeansException {

	Object result = existingBean;
	for (BeanPostProcessor processor : getBeanPostProcessors()) {
		//当循环到processor=CommonAnnotationBeanPostProcessor时，点击进入分析
		Object current = processor.postProcessBeforeInitialization(result, beanName);
		if (current == null) {
			return result;
		}
		result = current;
	}
	return result;
}

CommonAnnotationBeanPostProcessor继承了InitDestroyAnnotationBeanPostProcessor，postProcessBeforeInitialization(Object bean, String beanName)方法在父类中

InitDestroyAnnotationBeanPostProcessor#postProcessBeforeInitialization

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
	LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
	try {
		metadata.invokeInitMethods(bean, beanName);
	}
	catch (InvocationTargetException ex) {
		throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());
	}
	catch (Throwable ex) {
		throw new BeanCreationException(beanName, "Failed to invoke init method", ex);
	}
	return bean;
}

InitDestroyAnnotationBeanPostProcessor.LifecycleMetadata#invokeInitMethods

public void invokeInitMethods(Object target, String beanName) throws Throwable {
  Collection<LifecycleElement> checkedInitMethods = this.checkedInitMethods;
  Collection<LifecycleElement> initMethodsToIterate =
      (checkedInitMethods != null ? checkedInitMethods : this.initMethods);
  if (!initMethodsToIterate.isEmpty()) {
    for (LifecycleElement element : initMethodsToIterate) {
      if (logger.isTraceEnabled()) {
        logger.trace("Invoking init method on bean '" + beanName + "': " + element.getMethod());
      }
      //在这里反射执行带有@PostConstruct注解的方法
      element.invoke(target);
    }
  }
}

ContextRefreshedEvent事件机制

进入SpringApplication#run(java.lang.String…)

public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	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();
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
		//这里进入就会执行经典的refresh方法进行容器创建工作
		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, listeners);
		throw new IllegalStateException(ex);
	}

	try {
		listeners.running(context);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, null);
		throw new IllegalStateException(ex);
	}
	return context;
}

进入AbstractApplicationContext#refresh

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);

			//在这个方法进行发布ContextRefreshedEvent事件
			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();
		}
	}
}

AbstractApplicationContext#finishRefresh

protected void finishRefresh() {
  // Clear context-level resource caches (such as ASM metadata from scanning).
  clearResourceCaches();

  // Initialize lifecycle processor for this context.
  initLifecycleProcessor();

  // Propagate refresh to lifecycle processor first.
  getLifecycleProcessor().onRefresh();

  // 这里进行真正的ContextRefreshedEvent事件发布
  publishEvent(new ContextRefreshedEvent(this));

  // Participate in LiveBeansView MBean, if active.
  LiveBeansView.registerApplicationContext(this);
}

AbstractApplicationContext#publishEvent

protected void publishEvent(Object event, @Nullable ResolvableType eventType) {
  Assert.notNull(event, "Event must not be null");

  // Decorate event as an ApplicationEvent if necessary
  ApplicationEvent applicationEvent;
  if (event instanceof ApplicationEvent) {
    applicationEvent = (ApplicationEvent) event;
  }
  else {
    applicationEvent = new PayloadApplicationEvent<>(this, event);
    if (eventType == null) {
      eventType = ((PayloadApplicationEvent<?>) applicationEvent).getResolvableType();
    }
  }

  // Multicast right now if possible - or lazily once the multicaster is initialized
  if (this.earlyApplicationEvents != null) {
    this.earlyApplicationEvents.add(applicationEvent);
  }
  else {
    //通过spring的applicationContext进行ContextRefreshedEvent事件发布
    getApplicationEventMulticaster().multicastEvent(applicationEvent, eventType);
  }

  // Publish event via parent context as well...
  if (this.parent != null) {
    if (this.parent instanceof AbstractApplicationContext) {
      //如果执行到这里说明是有的bean依赖了微服务Feign的接口，springboot就会生成Feign的接口的bean，
      //每个feign会有自己spring上下文容器是为了集成ribbon的配置，这里的parent就是父容器也就是springboot本身的上下文容器
      ((AbstractApplicationContext) this.parent).publishEvent(event, eventType);
    }
    else {
      this.parent.publishEvent(event);
    }
  }
}

ApplicationStartedEvent事件机制

依旧进入SpringApplication#run(java.lang.String…)

public ConfigurableApplicationContext run(String... args) {
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	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();
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
		refreshContext(context);
		afterRefresh(context, applicationArguments);
		stopWatch.stop();
		if (this.logStartupInfo) {
			new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
		}
    //在这里就进行ApplicationStartedEvent事件的发布
		listeners.started(context);
		callRunners(context, applicationArguments);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, listeners);
		throw new IllegalStateException(ex);
	}

	try {
		listeners.running(context);
	}
	catch (Throwable ex) {
		handleRunFailure(context, ex, null);
		throw new IllegalStateException(ex);
	}
	return context;
}

EventPublishingRunListener#started

public void started(ConfigurableApplicationContext context) {
  //进行ApplicationStartedEvent事件的发布
  context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context));
  AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
}

总结

执行顺序，1 @PostConstruct执行 2 ContextRefreshedEvent事件 3 ApplicationStartedEvent事件

细节问题

在实际项目中发现ContextRefreshedEvent事件先于@PostConstruct执行，并且会执行多次。

原因

• 这是因为项目是Springcloud引入了Feign的微服务，当执行将所有的懒加载对象进行生成这个步骤时
• 如果有的bean依赖了微服务Feign的接口，springboot就会生成Feign的接口的bean
• 每个feign会有自己spring上下文容器是为了集成ribbon的配置，这里的parent就是父容器也就是springboot本身的上下文容器
• 所以只要有的bean依赖了微服务Feign的接口，在进行fegin的实际生成时会有自己的spring上下文，就会发布一遍ContextRefreshedEvent事件

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