spring后置处理器

1、BeanFactoryPostProcessor

1.1、 BeanFactoryPostProcessor子接口及关系

1.2、BeanDefinitionRegistryPostProcessor

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

    /**
     * 此时所有常规 bean 定义(BeanDefinition)都已被加载，但尚未实例化任何 bean。
     * 这允许在下一个后处理阶段开始之前添加更多的 bean 定义。
	 * Modify the application context's internal bean definition registry after its
	 * standard initialization. All regular bean definitions will have been loaded,
	 * but no beans will have been instantiated yet. This allows for adding further
	 * bean definitions before the next post-processing phase kicks in.
	 * @param registry the bean definition registry used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;

}

BeanDefinitionRegistryPostProcessor继承自BeanFactoryPostProcessor；
其执行时机在:
org.springframework.context.support.AbstractApplicationContext#refresh --调用–> org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors --调用–>
org.springframework.context.support.PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors(org.springframework.beans.factory.config.ConfigurableListableBeanFactory, java.util.List)

执行时，按实现的优先级接口(PriorityOrdered、Ordered、不实现)顺序执行对应的postProcessBeanDefinitionRegistry方法；
待所有BeanDefinitionRegistryPostProcessor的postProcessBeanDefinitionRegistry方法执行完成后，再统一执行org.springframework.beans.factory.config.BeanFactoryPostProcessor#postProcessBeanFactory

org.springframework.context.annotation.ConfigurationClassPostProcessor(配置类的解析后置处理器)就是实现的BeanDefinitionRegistryPostProcessor接口

1.3、BeanFactoryPostProcessor

@FunctionalInterface
public interface BeanFactoryPostProcessor {

	/**
     * 所有 bean 定义都已被加载，但还没有 bean 被实例化。这允许覆盖或添加属性，甚至是提前初始化的 bean。
	 * Modify the application context's internal bean factory after its standard
	 * initialization. All bean definitions will have been loaded, but no beans
	 * will have been instantiated yet. This allows for overriding or adding
	 * properties even to eager-initializing beans.
	 * @param beanFactory the bean factory used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

其执行时机同BeanDefinitionRegistryPostProcessor；同样按实现的优先级接口(PriorityOrdered、Ordered、不实现)顺序执行

2、BeanPostProcessor

2.1、BeanPostProcessor子接口及关系

BeanPostProcessor注册时机:
org.springframework.context.support.AbstractApplicationContext#registerBeanPostProcessors --调用–>
org.springframework.context.support.PostProcessorRegistrationDelegate#registerBeanPostProcessors(org.springframework.beans.factory.config.ConfigurableListableBeanFactory, org.springframework.context.support.AbstractApplicationContext)

2.2、SmartInstantiationAwareBeanPostProcessor

public interface SmartInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessor {

	/**
     * 返回Bean的类型，一个“指鹿为马”的机会；org.springframework.beans.factory.support.DefaultListableBeanFactory#doGetBeanNamesForType就会用到该方法
     * 预测postProcessBeforeInstantiation方法返回的对象类型
	 */
	@Nullable
	default Class<?> predictBeanType(Class<?> beanClass, String beanName) throws BeansException {
		return null;
	}

	/**
     * 可以使用该方法的实现在创建bean时使用指定的构造方法
	 */
	@Nullable
	default Constructor<?>[] determineCandidateConstructors(Class<?> beanClass, String beanName)
			throws BeansException {

		return null;
	}

	/**
	 * 获取对指定 bean 的早期访问的引用，通常用于解析循环引用
	 */
	default Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {
		return bean;
	}

}

调用org.springframework.beans.factory.support.DefaultListableBeanFactory#doGetBeanNamesForType时会触发predictBeanType方法

2.3、InstantiationAwareBeanPostProcessor

public interface InstantiationAwareBeanPostProcessor extends BeanPostProcessor {

	/**
     * 在目标 bean 被实例化之前调用。返回的 bean 对象可能是要使用的代理而不是目标 bean，从而有效地抑制了目标 bean 的默认实例化。
     * 如果这个方法返回了一个非空的对象，那么bean的创建过程就会短路。
	 */
	@Nullable
	default Object postProcessBeforeInstantiation(Class<?> beanClass, String beanName) throws BeansException {
		return null;
	}

	/**
     * 在通过构造函数或工厂方法实例化 bean 之后，但在 Spring 属性填充（来自显式属性或自动装配）发生之前执行操作。在org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#populateBean里
     * 这是在给定 bean 实例上执行自定义字段注入的理想回调，就在 Spring 的自动装配开始之前。
     * 默认实现返回true，返回false将直接退出populateBean方法，后续属性不再赋值
	 */
	default boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {
		return true;
	}

	/**
     * 在工厂将给定的属性值应用到给定的 bean 之前对其进行后处理
	 * Spring的自动装配后置处理器就是在这里实现，其返回的PropertyValues会被org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory#applyPropertyValues使用，赋值
	 */
	@Nullable
	default PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)
			throws BeansException {

		return null;
	}

	/**
	 * @deprecated as of 5.1, in favor of {@link #postProcessProperties(PropertyValues, Object, String)}
	 */
	@Deprecated
	@Nullable
	default PropertyValues postProcessPropertyValues(
			PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {

		return pvs;
	}

}

2.4、MergedBeanDefinitionPostProcessor

public interface MergedBeanDefinitionPostProcessor extends BeanPostProcessor {

	/**
	 * 对指定 bean 的给定合并 bean 定义进行后处理
     * 在实例化bean之前执行，在InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation之前执行
	 */
	void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class<?> beanType, String beanName);

	/**
	 * A notification that the bean definition for the specified name has been reset,
	 * and that this post-processor should clear any metadata for the affected bean.
	 * 
The default implementation is empty.
	 * @param beanName the name of the bean
	 * @since 5.1
	 * @see DefaultListableBeanFactory#resetBeanDefinition
	 */
	default void resetBeanDefinition(String beanName) {
	}

}

2.5、BeanPostProcessor

public interface BeanPostProcessor {

	/**
	 * 执行此方法时，bean已创建，但尚未初始化
     * 实例：ApplicationContextAwareProcessor注入ApplicationEventPublisherAware、ApplicationContextAware、
     * MessageSourceAware、ResourceLoaderAware、EnvironmentAware、EmbeddedValueResolverAware、ApplicationStartupAware
	 */
	@Nullable
	default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

	/**
	 * 初始化完成之后再对Bean属性修改，此时org.springframework.beans.factory.InitializingBean#afterPropertiesSet、自定义init方法已执行
	 */
	@Nullable
	default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
		return bean;
	}

}