spring IoC （八）Bean对IoC容器的感知

　　容器管理的Bean一般不需要了解容器的状态和直接使用容器，但在某些情况下，是需要在Bean中直接

对IoC容器进行操作的，这时候，就需要在Bean中设定对容器的感知。Spring IoC容器也提供了该功能，它

是通过特定的aware接口来完成的。例如BeanNameAware、BeanFactorAware、ApplicationContextAware

、MessageSourceAware、ResourceLoaderAware等。

　　在 Bean实例化后，初始化前会调用BeanPostProcessor.postProcessBeforeInitialization

AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization() -->

BeanPostProcessor.postProcessBeforeInitialization(Object, String)

例如ApplicationContextAwareProcessor中

    public Object postProcessBeforeInitialization(final Object bean, String beanName) throws BeansException {
        AccessControlContext acc = null;

        if (System.getSecurityManager() != null &&
                (bean instanceof EnvironmentAware || bean instanceof EmbeddedValueResolverAware ||
                        bean instanceof ResourceLoaderAware || bean instanceof ApplicationEventPublisherAware ||
                        bean instanceof MessageSourceAware || bean instanceof ApplicationContextAware)) {
            acc = this.applicationContext.getBeanFactory().getAccessControlContext();
        }

        if (acc != null) {
            AccessController.doPrivileged(new PrivilegedAction<Object>() {
                public Object run() {
                    invokeAwareInterfaces(bean);
                    return null;
                }
            }, acc);
        }
        else {
            invokeAwareInterfaces(bean);
        }

        return bean;
    }

    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(
                        new EmbeddedValueResolver(this.applicationContext.getBeanFactory()));
            }
            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);
            }
        }
    }