spring Aware接口

14 Aware 实现分析

通过前面深入理解spring生命周期与BeanPostProcessor的实现原理分析，我们知道Aware的实现是通过BeanPostProcessor
实现的，我们以ApplicationContextAware做分析,实现接口是使用ApplicationContextAwareProcessor接口完成Aware注入，代码如下

class ApplicationContextAwareProcessor implements BeanPostProcessor {

	private final ConfigurableApplicationContext applicationContext;

	private final StringValueResolver embeddedValueResolver;


	/**
	 * Create a new ApplicationContextAwareProcessor for the given context.
	 */
	public ApplicationContextAwareProcessor(ConfigurableApplicationContext applicationContext) {
		this.applicationContext = applicationContext;
		this.embeddedValueResolver = new EmbeddedValueResolver(applicationContext.getBeanFactory());
	}


	@Override
	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>() {
				@Override
				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(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);
			}
		}
	}

	@Override
	public Object postProcessAfterInitialization(Object bean, String beanName) {
		return bean;
	}

}

在上述代码invokeAwareInterfaces中我们可以看的，每一个初始化的bean 是否实现其中的Aware接口，并回调注入参数属性，类似函数回调方式

要想实现自己的组件，我们也可以安装spring的实现方式，提供一个BeanPostProcessor接口，并在初始化时判断bean是否实现自定义的Aware接口，如果实现时，通过回调方式调用接口方法

Aware常用的实现类

• ApplicationContextAware 自动注入IOC容器
• ApplicationEventPublisherAware 注入事件派发器
• BeanClassLoaderAware 类加载器
• BeanFactoryAware Bean工厂
• BeanNameAware Bean名字
• EmbeddedValueResolverAware Embedded值解析器
• EnvironmentAware 环境
• ImportAware 导入相关的
• LoadTimeWeaverAware 导入相关的
• MessageSourceAware 国际化
• NotificationPublisherAware 发送通知的支持
• ResourceLoaderAware 资源加载器