Spring各种PostProcessor : BeanPostProcessor

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概述

顾名思义， BeanPostProcessor定义了关于Bean的PostProcessor。这里的Bean就是我们一般意义上所说的bean容器中的bean实例了。

Spring容器在每个bean实例创建过程中bean实例初始化前后调用接口BeanPostProcessor定义的方法。

BeanPostProcessor接口定义了两个方法:

• Object postProcessBeforeInitialization(Object bean, String beanName)
• Object postProcessAfterInitialization(Object bean, String beanName)

这两个方法的执行时机如下图所示 :

以上流程的具体代码可以参考AbstractAutowireCapableBeanFactory#doCreateBean方法实现。

上图中的bean初始化指的是以下几种情况 :

1. 通过InitializingBean接口实现的afterPropertiesSet()方法;
2. xml方式指定的bean的 init-method 初始化方法;
3. JSR-250 注解 @PostConstruct 注解的初始化方法;
4. Java 配置类中 @Bean(initMethod = "init") 指定的初始化方法;

源代码解析

/**
 * 
 * 对新的bean实例进行订制化修改的factory hook。
 * ApplicationContexts can autodetect BeanPostProcessor beans in their
 * bean definitions and apply them to any beans subsequently created.
 * 
 * 应用程序上下文ApplicationContext能够从自己的bean定义中自动检测BeanPostProcessor bean，
 * 并随后在任意bean创建时应用到新创建的bean。
 * 
 * @author Juergen Hoeller
 * @since 10.10.2003
 * @see InstantiationAwareBeanPostProcessor
 * @see DestructionAwareBeanPostProcessor
 * @see ConfigurableBeanFactory#addBeanPostProcessor
 * @see BeanFactoryPostProcessor
 */
public interface BeanPostProcessor {

	/**
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if null, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 */
	Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException;

	/**
	 * In case of a FactoryBean, this callback will be invoked for both the FactoryBean
	 * instance and the objects created by the FactoryBean (as of Spring 2.0). The
	 * post-processor can decide whether to apply to either the FactoryBean or created
	 * objects or both through corresponding bean instanceof FactoryBean checks.
	 * 
	 * This callback will also be invoked after a short-circuiting triggered by a
	 * InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation method,
	 * in contrast to all other BeanPostProcessor callbacks.
	 * 
	 * @param bean the new bean instance
	 * @param beanName the name of the bean
	 * @return the bean instance to use, either the original or a wrapped one;
	 * if null, no subsequent BeanPostProcessors will be invoked
	 * @throws org.springframework.beans.BeansException in case of errors
	 * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
	 * @see org.springframework.beans.factory.FactoryBean
	 */
	Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException;

}

参考文章

Springboot Servlet Web 项目中内置BeanPostProcessor清单