spring之ApplicationContextAware详解

一、进入正题

Aware本义就是"自动的",顾名思义spring给我们自动做了些事情。spring有很多以Aware结尾的类,有EnvironmentAware、ApplicationContextAware、MessageSourceAware等。这里我主要讲一下ApplicationContextAware。

二、使用

  @Service("gatewayService")
public class GatewayServiceImpl implements IGatewayService,ApplicationContextAware {

    private Logger logger= LoggerFactory.getLogger(getClass());


    Map chargeHandlerMap=new HashMap();

    private ApplicationContext applicationContext;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext)
            throws BeansException {
        this.applicationContext=applicationContext;
    }
}

在我们需要使用ApplicationContext的服务中实现ApplicationContextAware接口,系统启动时就可以自动给我们的服务注入applicationContext对象,我们就可以获取到ApplicationContext里的所有信息了。

三、原理分析

我们都知道spring的入口方法就在AbstractApplicationContext的refresh()方法.我们先去看看refresh().prepareBeanFactory()方法。

protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        // Tell the internal bean factory to use the context's class loader etc.
        beanFactory.setBeanClassLoader(getClassLoader());
        beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
        beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));

        // 添加ApplicationContextAware的处理器
        beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
        beanFactory.ignoreDependencyInterface(EnvironmentAware.class);
        beanFactory.ignoreDependencyInterface(EmbeddedValueResolverAware.class);
        beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);
        beanFactory.ignoreDependencyInterface(MessageSourceAware.class);
        beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);
                ...
    }

也就是说,spring在启动的时候给我们添加了ApplicationContextAwareProcessor这样一个processor。进去看看它的实现:

@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