BeanFactoryPostProcessor

与 BeanPostProcessor 类似

• BeanFactoryPostProcessor
  • When load BeanFactoryPostProcessor
  • The hook method postProcessBeanFactory
  • The load method PostProcessorRegistrationDelegate
    • PostProcessorRegistrationDelegate-registerBeanPostProcessors
  • Demo for BeanFactoryPostProcessor
    • PropertyResourceConfigurer
    • ConfigurationClassPostProcessor

When load BeanFactoryPostProcessor

BeanFactoryPostProcessor 的作用,在 AbstractApplicationContext.refresh 中有下面的注释

/**
 * Allows for custom modification of an application context's bean definitions,
 * adapting the bean property values of the context's underlying bean factory.
 *
 * <p>Application contexts can auto-detect BeanFactoryPostProcessor beans in
 * their bean definitions and apply them before any other beans get created.
 *
 * <p>Useful for custom config files targeted at system administrators that
 * override bean properties configured in the application context.
 *
 * <p>See PropertyResourceConfigurer and its concrete implementations
 * for out-of-the-box solutions that address such configuration needs.
 *
 * <p>A BeanFactoryPostProcessor may interact with and modify bean
 * definitions, but never bean instances. Doing so may cause premature bean
 * instantiation, violating the container and causing unintended side-effects.
 * If bean instance interaction is required, consider implementing
 * {@link BeanPostProcessor} instead.
 */

// AbstractApplicationContext
@Override
public void refresh() throws BeansException, IllegalStateException {

// ...
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory)
// ...
}

The hook method postProcessBeanFactory

@FunctionalInterface
public interface BeanFactoryPostProcessor {
 /**
  * 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;
}

The load method PostProcessorRegistrationDelegate

PostProcessorRegistrationDelegate 是一个工具类

PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

初始化实现了 BeanFactoryPostProcessor和 BeanDefinitionRegistry 接口的类

PostProcessorRegistrationDelegate-registerBeanPostProcessors

public static void registerBeanPostProcessors(
ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

}

Demo for BeanFactoryPostProcessor

PropertyResourceConfigurer

PropertyResourceConfigurer Spring 实现 ${} 占位符注入的 BeanFactoryPostProcessor 一种实现

ConfigurationClassPostProcessor

ConfigurationClassPostProcessor 主要负责 @Configuration 注解的解析

• @Configuration

// ConfigurationClassPostProcessor
public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
             PriorityOrdered, ResourceLoaderAware, BeanClassLoaderAware, EnvironmentAware {
}
// BeanFactoryPostProcessor
public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
//
}