SpringBoot自动装配深入理解(10)

/**
 * Extension to the standard {@link BeanFactoryPostProcessor} SPI, allowing for
 * the registration of further bean definitions <i>before</i> regular
 * BeanFactoryPostProcessor detection kicks in. In particular,
 * BeanDefinitionRegistryPostProcessor may register further bean definitions
 * which in turn define BeanFactoryPostProcessor instances.
 *
 * @author Juergen Hoeller
 * @since 3.0.1
 * @see org.springframework.context.annotation.ConfigurationClassPostProcessor
 */
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;

}

该接口继承了BeanFactoryPostProcessor。

2.2、ConfigurationClassPostProcessor 类

  该类主要处理@Configuration注解的,它实现了BeanDefinitionRegistryPostProcessor,  那么也间接实现了BeanFactoryPostProcessor,关键代码如下:

@Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
        int factoryId = System.identityHashCode(beanFactory);
        if (this.factoriesPostProcessed.contains(factoryId)) {
            throw new IllegalStateException(
                    "postProcessBeanFactory already called on this post-processor against " + beanFactory);
        }
        this.factoriesPostProcessed.add(factoryId);
        if (!this.registriesPostProcessed.contains(factoryId)) {
            // BeanDefinitionRegistryPostProcessor hook apparently not supported...
            // Simply call processConfigurationClasses lazily at this point then.
            processConfigBeanDefinitions((BeanDefinitionRegistry) beanFactory);
        }

enhanceConfigurationClasses(beanFactory);
        beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
    }

/**
    * Build and validate a configuration model based on the registry of
    * {@link Configuration} classes.
    */
    public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
        //.....省略部分代码

// Parse each @Configuration class
        ConfigurationClassParser parser = new ConfigurationClassParser(
                this.metadataReaderFactory, this.problemReporter, this.environment,
                this.resourceLoader, this.componentScanBeanNameGenerator, registry);

Set<BeanDefinitionHolder> candidates = new LinkedHashSet<BeanDefinitionHolder>(configCandidates);
        Set<ConfigurationClass> alreadyParsed = new HashSet<ConfigurationClass>(configCandidates.size());
        do {
            parser.parse(candidates);
            parser.validate();

Set<ConfigurationClass> configClasses = new LinkedHashSet<ConfigurationClass>(parser.getConfigurationClasses());
            configClasses.removeAll(alreadyParsed);

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