spring扩展点系列：BeanDefinitionRegistryPostProcessor

[TFdream]

BeanDefinitionRegistryPostProcessor 定义如下：

package org.springframework.beans.factory.support;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {

    /**
     * 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;

}

不难发现，BeanDefinitionRegistryPostProcessor是继承BeanFactoryPostProcessor

public abstract class AbstractApplicationContext extends DefaultResourceLoader
        implements ConfigurableApplicationContext, DisposableBean {

    @Override
    public void refresh() throws BeansException, IllegalStateException {
        synchronized (this.startupShutdownMonitor) {
            // Prepare this context for refreshing.
            prepareRefresh();

            // Tell the subclass to refresh the internal bean factory.
            ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

            // Prepare the bean factory for use in this context.
            prepareBeanFactory(beanFactory);

            try {
                // 子类扩展点（空实现）
                postProcessBeanFactory(beanFactory);

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

                // Register bean processors that intercept bean creation.
                registerBeanPostProcessors(beanFactory);

                // Initialize message source for this context.
                initMessageSource();

                // Initialize event multicaster for this context.
                initApplicationEventMulticaster();

                // 子类扩展点（空实现）
                onRefresh();

                // Check for listener beans and register them.
                registerListeners();

                // 实例化单例bean
                finishBeanFactoryInitialization(beanFactory);

                // Last step: publish corresponding event.
                finishRefresh();
            } catch (BeansException ex) {
                if (logger.isWarnEnabled()) {
                    logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
                }

                // Destroy already created singletons to avoid dangling resources.
                destroyBeans();

                // Reset 'active' flag.
                cancelRefresh(ex);

                // Propagate exception to caller.
                throw ex;
            } finally {
                // Reset common introspection caches in Spring's core, since we
                // might not ever need metadata for singleton beans anymore...
                resetCommonCaches();
            }
        }
    }

    /**
     * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
     * respecting explicit order if given.
     * <p>Must be called before singleton instantiation.
     */
    protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
        PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

        // Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
        // (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
        if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
            beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
            beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
        }
    }
}