探究实现Aware接口的原理及使用

/**
 * 只做标记
 * spring容器感知接口
 */
public interface Aware {
}

public interface ApplicationContextAware extends Aware {
    void setApplicationContext(ApplicationContext applicationContext);
}

public interface BeanClassLoaderAware extends Aware{
    void setBeanClassLoader(ClassLoader classLoader);
}

public interface BeanFactoryAware extends Aware{
    void setBeanFactory(BeanFactory beanFactory) throws BeansException;
}

public interface BeanNameAware extends Aware{
    void setBeanName(String beanName);
}

@Override
    protected Object createBean(String beanName, BeanDefinition beanDefinition, Object[] args) {
        Object bean = null;
        try {
            bean = createBeanInstance(beanDefinition, beanName, args);
            // 注入属性
            applyPropertyValues(beanName, bean, beanDefinition);
            // 提供给外部的扩展包装，执行 Bean 的初始化方法和 BeanPostProcessor 的前置和后置处理方法
            bean = initializeBean(beanName, bean, beanDefinition);
        } catch (Exception e) {
            throw new RuntimeException("bean create error!", e);
        }
        // 注册实现了 DisposableBean 接口的 Bean 对象
        registerDisposableBeanIfNecessary(beanName, bean, beanDefinition);
        registerSingleton(beanName, bean);
        return bean;
    }
private Object initializeBean(String beanName, Object bean, BeanDefinition beanDefinition) throws BeansException {
        if (bean instanceof Aware) {
            if (bean instanceof BeanFactoryAware) {
                ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
            }
            if (bean instanceof ApplicationContextAware) {
                ((ApplicationContextAware) bean).setApplicationContext(this);
            }
            if (bean instanceof BeanClassLoaderAware) {
                ((BeanClassLoaderAware) bean).setBeanClassLoader(getClassLoader());
            }
            if (bean instanceof BeanNameAware) {
                ((BeanNameAware) bean).setBeanName(beanName);
            }
        }
		.....
	}

public class UserService implements InitializingBean, DisposableBean, ApplicationContextAware, BeanClassLoaderAware, BeanNameAware {
    private ApplicationContext applicationContext;
    private ClassLoader classLoader;
    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        this.classLoader = classLoader;
    }
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) {
        this.applicationContext = applicationContext;
    }
}
@Test
    public void testContext1() throws BeansException {
        ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:spring.xml");
        applicationContext.registerShutdownHook();
        UserService userService = (UserService) applicationContext.getBean("userService");
        System.out.println(userService.say());
        System.out.println(userService.getApplicationContext());
        System.out.println(userService.getClassLoader());
        System.out.println(userService.getBeanName());
    }