ApplicationContextAware和BeanFactoryAware使用理解

1.Spring容器会自动把上下文环境对象调用ApplicationContextAware接口中的setApplicationContext方法;当一个类实现了这个接口之后,这个类就可以非常方便的获取到ApplicationContext中的所有的bean;简而言之,言而总之,此类可以获取到spring配置文件中所有的bean对象。

2.基本原理见如下代码,核心类:ApplicationContextAwareProcessor

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() {
			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);
		}
	}
} 
  

在启动Spring容器创建bean的时候会执行postProcessBeforeInitialization这个方法,发现实现了Aware接口的类(例如最后一个ApplicationContextAware),都会加载spring的applicationContext。

3.代码实例讲解(此处讲解通过实现BeanFactoryAware接口将bean注册到beanfactory中):
首先通过实现BeanFactoryAware接口将bean注册到spring容器中。

@Component
public class BeanFactoryHelper implements BeanFactoryAware {

    private static BeanFactory beanFactory;

    @Override
    public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
        this.beanFactory = beanFactory;
    }

    public static BeanFactory getBeanFactory() {
        return this.beanFactory;
    }
}

//获取beanFactory并注册到spring上下文中
DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) BeanFactoryHolder.getBeanFactory();

String beanName = "test";
beanFactory.destroySingleton(beanName);

beanFactory.registerSingleton(beanName, singletonObject);

注册到spring上下文之后就可以通过实现ApplicationContextAware接口来获取bean对象:

@Component
public class ApplicationContextHelper implements ApplicationContextAware {
    private static ApplicationContext ctx;

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

    public static ApplicationContext getApplicationContext() {
        return this.ctx;
    }

    public static Object getBean(String beanName) {
        return this.ctx.getBean(beanName);
    }

    public static  T getBean(Class clazz) {
        return this.ctx.getBean(clazz);
    }

    public static  T getBean(String beanName, Class clazz) {
        try {
            return this.ctx.getBean(beanName, clazz);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

有问题欢迎各位一起讨论交流。

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