spring(三)：spring中BeanPostProcessor的使用

spring中实现BeanPostProcessor的后置处理器

ApplicationContextAwareProcessor

进入该实现类内部

可以看到：该类帮我们组建IOC容器，判断我们的bean有没有实现ApplicationContextAware接口，并作出相应处理(setApplicationContext方法)

测试：调试一个实现ApplicationContextAware接口的类的创建过程

public class User implements ApplicationContextAware {
    private ApplicationContext applicationContext;

    public User(){
        System.out.println("User...constructor....");
    }

    @PostConstruct
    public void init(){
        System.out.println("User...init....");
    }

    @PreDestroy
    public void destroy(){
        System.out.println("User...destroy....");
    }
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        /**
         * 容器初始化，将applicationContext作为参数传入，其它方法就可以使用容器了
         * 该方法是由ApplicationContextAwareProcessor处理器来执行的
         */
        this.applicationContext = applicationContext;
    }
}

在ApplicationContextAwareProcessor类的postProcessBeforeInitialization方法中添加断点

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)) {//1
		acc = this.applicationContext.getBeanFactory().getAccessControlContext();
	}

	if (acc != null) {
		AccessController.doPrivileged(new PrivilegedAction<Object>() {
			public Object run() {
				ApplicationContextAwareProcessor.this.invokeAwareInterfaces(bean);
				return null;
			}
		}, acc);
	} else {
		this.invokeAwareInterfaces(bean);//2
	}

	return bean;
}

注释1：创建User对象，初始化之前，先判断User类是否实现了ApplicationContextAware接口

注释2：调用invokeAwareInterfaces方法给bean设置值

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);
		}
	}

}

invokeAwareInterfaces方法中判断该bean属于哪个Aware实例，并进行相应设值处理。如果Aware是ApplicationContextAware，就将当前bean转成ApplicationContextAware类型并调用setApplicationContext方法将ApplicationContext值设置到bean中

调试：

　　在bean是User类型时，setApplicationContext方法会得到执行，也即user对象中设置了ioc容器，可以在user的其它方法中使用该容器

BeanValidationPostProcessor

数据校验

常用

　　对象创建完成，bean对象属性赋值后，web中应用比较多

　　对页面提交的值进行校验

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
	if (!this.afterInitialization) {
		this.doValidate(bean);
	}

	return bean;
}

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
	if (this.afterInitialization) {
		this.doValidate(bean);
	}

	return bean;
}

postProcessBeforeInitialization方法用于初始化前校验

postProcessAfterInitialization方法用于初始化后校验

InitDestroyAnnotationBeanPostProcessor

该处理器用于处理@PostConstruct、@PreDestroy注解

利用反射调用bean生命周期的相关方法