시작

Bean이 Destory되는 과정을 한번 찾아가보자

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SpringApplicationShutdownHook.class

SpringApplicationShutdownHook.class

@Override
public void run() {
	...
    contexts.forEach(this::closeAndWait);
    closedContexts.forEach(this::closeAndWait);
    ...
}

private void closeAndWait(ConfigurableApplicationContext context) {
	if (!context.isActive()) {
    	return;
	}
	context.close();
    ...
}

AbstractApplicationContext.class

@Override
public void close() {
	synchronized (this.startupShutdownMonitor) {
    	doClose();
        ...
    }
}

protected void doClose() {
	...
    destroyBeans();
    ...
}

protected void destroyBeans() {
	getBeanFactory().destroySingletons();
}

DefaultSingletonBeanRegistry.class

public void destroySingletons() {
	for (int i = disposableBeanNames.length - 1; i >= 0; i--) {
		destroySingleton(disposableBeanNames[i]);
    }	
}

public void destroySingleton(String beanName) {
	...
    destroyBean(beanName, disposableBean);
}

protected void destroyBean(String beanName, @Nullable DisposableBean bean) {
	...
    if (bean != null) {
    	try {
        	bean.destroy();
		}
    }
    ...
}

SpringApplicationShutdownHook Thread가 시작하게되면 위와같은 과정을 거쳐 bean이 destory하게 된다

ApplicationContextClosedListener

@Override
public void onApplicationEvent(ContextClosedEvent event) {
	synchronized (SpringApplicationShutdownHook.class) {
    	ApplicationContext applicationContext = event.getApplicationContext();
        SpringApplicationShutdownHook.this.contexts.remove(applicationContext);
        SpringApplicationShutdownHook.this.closedContexts.add((ConfigurableApplicationContext) applicationContext);
    }
}

ContextClosedEvent가 발생하게 되면 해당 Context를 ShutdownHook에 추가한다

SpringBoot가 run될때 EventListener로 등록되는것도 볼 수 있다

정확하진 않지만 추측상 해당 Listener는 EventMulticaster에 의해 Async로 실행되는거 같다