ApplicationContextAware的使用理解

想象這麼一個場景，一個單例bean中依賴有原型bean我們怎麼去注入？

spring中我瞭解的大致有兩種方式，一種是@Lookup依賴查找，另一種就是實現ApplicationContextAware 

---

使用方法

@Service
@Scope("prototype")
public class UserService {
	
}

@Component
public class UserService2 implements ApplicationContextAware {
	private ApplicationContext context;
	@Override
	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
		this.context = applicationContext;
	}

	public void test(){
		UserService service = context.getBean(UserService.class);
		System.out.println(service);
	}
}

爲什麼我們實現這個接口就能拿到ApplicationContext？

首先在spring容器啓動的時候,有添加一個ApplicationContextAwareProcessor

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		
		// Configure the bean factory with context callbacks.
		// 在beanFactory中添加ApplicationContextAwareProcessor，如果自定義類中有實現ApplicationContextAware就能拿到ApplicationContext
		beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
		
}

ApplicationContextAwareProcessor是BeanPostProcessor的實現在容器初始化過程中會執行所有的BeanPostProcessor

@Override
public void refresh() throws BeansException, IllegalStateException {
	// 前後代碼就刪掉了
	// Invoke factory processors registered as beans in the context.
	invokeBeanFactoryPostProcessors(beanFactory);

				
}

在ApplicationContextAwareProcessor有這麼一段,如果一個bean是ApplicationContextAware的實現，就調用它的set方法傳入spring context

private void invokeAwareInterfaces(Object bean) {
		
		if (bean instanceof ApplicationContextAware) {
			((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
		}
	}