Spring扩展接口-InstantiationAwareBeanPostProcessor

简介

在bean创建过程中，Spring提供了扩展接口InstantiationAwareBeanPostProcessor扩展bean创建功能。

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {
    
    Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException;
    
    boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException;
    
    PropertyValues postProcessPropertyValues(
			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName)
			throws BeansException;  
}

该接口有三个方法：

• postProcessBeforeInstantiation

在目标bean开始实例化前调用该方法，实现该方法可以实现返回bean的代理而非bean本身。如果返回的Object不为空，那么则说明这个类不需要Spring来进行实例化且后序自动装配、bean初始化回调等也不会被执行，该bean直接放到Spring容器中。

• postProcessAfterInstantiation

在bean被实例化之后，在Spring属性填充（from explicit properties or autowiring）发生之前。当然返回结果为true时，说明应该为bean设置属性。如果返回结果为false，跳过bean属性赋值环节。

• postProcessPropertyValues

在工厂将给定的属性值应用于给定的bean之前，对其进行后处理。

用途示例

Spring代理AbstractAutoProxyCreator

postProcessBeforeInstantiation方法，尝试创建一个代理对象返回。

	@Override
	public Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
		Object cacheKey = getCacheKey(beanClass, beanName);

		if (beanName == null || !this.targetSourcedBeans.contains(beanName)) {
			if (this.advisedBeans.containsKey(cacheKey)) {
				return null;
			}
			if (isInfrastructureClass(beanClass) || shouldSkip(beanClass, beanName)) {
				this.advisedBeans.put(cacheKey, Boolean.FALSE);
				return null;
			}
		}

		// Create proxy here if we have a custom TargetSource.
		// Suppresses unnecessary default instantiation of the target bean:
		// The TargetSource will handle target instances in a custom fashion.
		if (beanName != null) {
			TargetSource targetSource = getCustomTargetSource(beanClass, beanName);
			if (targetSource != null) {
				this.targetSourcedBeans.add(beanName);
				Object[] specificInterceptors = getAdvicesAndAdvisorsForBean(beanClass, beanName, targetSource);
				Object proxy = createProxy(beanClass, beanName, specificInterceptors, targetSource);
				this.proxyTypes.put(cacheKey, proxy.getClass());
				return proxy;
			}
		}

		return null;
	}

更多信息请移步Spring专栏：www.yuque.com/mrhuang-ire…

参考： [1].blog.csdn.net/J080624/art…