SpringBoot关闭过程中销毁DisposableBean解读

public void destroySingleton(String beanName) {
	// Remove a registered singleton of the given name, if any.
	// 从缓存中移除当前beanName
	removeSingleton(beanName);
	// Destroy the corresponding DisposableBean instance.
	// 从disposableBeans集合中移除当前 beanName
	DisposableBean disposableBean;
	synchronized (this.disposableBeans) {
		disposableBean = (DisposableBean) this.disposableBeans.remove(beanName);
	}
	// 这是核心方法
	destroyBean(beanName, disposableBean);
}

// DefaultSingletonBeanRegistry
protected void destroyBean(String beanName, @Nullable DisposableBean bean) {
	// Trigger destruction of dependent beans first...
	Set<String> dependencies;
	//dependentBeanMap存放的是哪些bean依赖于key
	synchronized (this.dependentBeanMap) {
		// Within full synchronization in order to guarantee a disconnected Set
		dependencies = this.dependentBeanMap.remove(beanName);
	}
	// 首先触发那些依赖于当前beanName的bean的销毁流程
	if (dependencies != null) {
		if (logger.isTraceEnabled()) {
			logger.trace("Retrieved dependent beans for bean '" + beanName + "': " + dependencies);
		}
		for (String dependentBeanName : dependencies) {
			destroySingleton(dependentBeanName);
		}
	}
	// Actually destroy the bean now...
	// bean销毁的过程入口，触发DisposableBeanAdapter的destroy方法
	if (bean != null) {
		try {
			bean.destroy();
		}
		catch (Throwable ex) {
			if (logger.isWarnEnabled()) {
				logger.warn("Destruction of bean with name '" + beanName + "' threw an exception", ex);
			}
		}
	}
	// Trigger destruction of contained beans...
	// 获取当前beanName对应的containedBeans，如果有，则遍历触发销毁流程
	Set<String> containedBeans;
	synchronized (this.containedBeanMap) {
		// Within full synchronization in order to guarantee a disconnected Set
		containedBeans = this.containedBeanMap.remove(beanName);
	}
	if (containedBeans != null) {
		for (String containedBeanName : containedBeans) {
			destroySingleton(containedBeanName);
		}
	}
	// Remove destroyed bean from other beans' dependencies.
	// 遍历dependentBeanMap的value，移除掉当前beanName。
	//之后如果value为空，其从dependentBeanMap移除掉当前entry
	synchronized (this.dependentBeanMap) {
		for (Iterator<Map.Entry<String, Set<String>>> it = this.dependentBeanMap.entrySet().iterator(); it.hasNext();) {
			Map.Entry<String, Set<String>> entry = it.next();
			Set<String> dependenciesToClean = entry.getValue();
			dependenciesToClean.remove(beanName);
			if (dependenciesToClean.isEmpty()) {
				it.remove();
			}
		}
	}
	// Remove destroyed bean's prepared dependency information.
	// 从 dependenciesForBeanMap中移除当前beanName对应的entry
	this.dependenciesForBeanMap.remove(beanName);
}

@Override
public void destroy() {
//获取当前实例维护的DestructionAwareBeanPostProcessor 触发其postProcessBeforeDestruction方法
	if (!CollectionUtils.isEmpty(this.beanPostProcessors)) {
		for (DestructionAwareBeanPostProcessor processor : this.beanPostProcessors) {
			processor.postProcessBeforeDestruction(this.bean, this.beanName);
		}
	}
// 是否触发destroy方法
	if (this.invokeDisposableBean) {
		if (logger.isTraceEnabled()) {
			logger.trace("Invoking destroy() on bean with name '" + this.beanName + "'");
		}
		try {
			if (System.getSecurityManager() != null) {
				AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
					((DisposableBean) this.bean).destroy();
					return null;
				}, this.acc);
			}
			else {
				((DisposableBean) this.bean).destroy();
			}
		}
		catch (Throwable ex) {
			String msg = "Invocation of destroy method failed on bean with name '" + this.beanName + "'";
			if (logger.isDebugEnabled()) {
				logger.warn(msg, ex);
			}
			else {
				logger.warn(msg + ": " + ex);
			}
		}
	}
// 如果destroyMethod 不为null，则触发自定义销毁方法
	if (this.destroyMethod != null) {
		invokeCustomDestroyMethod(this.destroyMethod);
	}
	else if (this.destroyMethodName != null) {
	// 如果destroyMethodName 不为null，则获取并触发自定义销毁方法
		Method methodToInvoke = determineDestroyMethod(this.destroyMethodName);
		if (methodToInvoke != null) {
			invokeCustomDestroyMethod(ClassUtils.getInterfaceMethodIfPossible(methodToInvoke));
		}
	}
}