实际项目开发中，会写类似如下的工具类，方便做脚本执行或者一些判断，提供一些api方法等(可阅读：https://blog.csdn.net/qq_26437925/article/details/114213391 ，ApplicationContextAware就大派用场了)，如下

@Component
public class SpringApplicationUtil implements ApplicationContextAware {private static ApplicationContext applicationContext;@Overridepublic void setApplicationContext(ApplicationContext applicationContext) throws BeansException {SpringApplicationUtil.applicationContext = applicationContext;}public static Object getBean(String beanName){return applicationContext.getBean(beanName);}public static List<String> getAllBeanNames(){String[] arr = applicationContext.getBeanDefinitionNames();if(arr == null || arr.length == 0){return new ArrayList<>();}return Arrays.stream(arr).collect(Collectors.toList());}}

如下测试代码, 想拿到某个bean, 直接从这个util拿到

@Testpublic void test2() throws Exception {ApplicationContext ctx =new AnnotationConfigApplicationContext(LocalConfig.class, LocalConfig2.class);// 直接从工具类获取UserService userService = (UserService)SpringApplicationUtil.getBean("userService");Assert.assertNotNull(userService);userService.add(new User());((AnnotationConfigApplicationContext) ctx).close();}

本文来探究一下它是如何工作的。

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直接debug可以看到执行链路，进行具体分析

可以发现在这个bean的初始化阶段，会执行所有的BeanPostProcessor扩展的postProcessBeforeInitialization方法，会发现执行到了ApplicationContextAwareProcessor

ApplicationContextAwareProcessor怎么来的？

org.springframework.context.support.AbstractApplicationContext的refresh方法中的prepareBeanFactory(beanFactory); 执行添加的，平台内置的一个beanPostProcessor

所以回到org.springframework.context.support.ApplicationContextAwareProcessor#postProcessBeforeInitialization 方法中，可以看到会执行Aware接口

private void invokeAwareInterfaces(Object bean) {if (bean instanceof Aware) {if (bean instanceof EnvironmentAware) {((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());}if (bean instanceof EmbeddedValueResolverAware) {((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(this.embeddedValueResolver);}if (bean instanceof ResourceLoaderAware) {((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);}if (bean instanceof ApplicationEventPublisherAware) {((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);}if (bean instanceof MessageSourceAware) {((MessageSourceAware) bean).setMessageSource(this.applicationContext);}if (bean instanceof ApplicationContextAware) {((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);}}
}

执行ApplicationContextAware的setApplicationContext方法完成设置, 如下

其实就是AnnotationConfigApplicationContext自身，即Spring容器管理者自身。

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再比如BeanAware接口, 一个Bean想知道自己的beanName，那么自己实现下BeanNameAware

public class X implements BeanNameAware {private String xName;@Autowiredprivate Y y;public X() {System.out.println("X()");}public void sy(){System.out.println("y:" + y);}@Overridepublic void setBeanName(String name) {this.xName = name;}public void sayMyName(){System.out.println("xName:" + xName);}