在spring启动过程中有个10多个关键的方法其中invokeBeanFactoryPostProcessors（）在函数在BeanDefinition完全加载后执行，实现的是spring  bean的后置增强器BeanFactoryPostProcessor。

        BeanFactoryPostProcessor在bean的生命周期中，主要增强的是BeanDefinition对象，对bean的定义信息增加。关键接口为：

postProcessBeanFactory

//实例化并调用所有注册的 BeanFactoryPostProcessor bean，如果给定，则遵守显式顺序。
必须在单一实例化之前调用。	
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 (!NativeDetector.inNativeImage() && beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));}}

invokeBeanFactoryPostProcessors:

if (beanFactory instanceof BeanDefinitionRegistry) {BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;List regularPostProcessors = new ArrayList<>();List registryProcessors = new ArrayList<>();//循环处理实现了BeanFactoryPostProcessor接口的增强器for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {BeanDefinitionRegistryPostProcessor registryProcessor =(BeanDefinitionRegistryPostProcessor) postProcessor;//注册更多的bean定义信息registryProcessor.postProcessBeanDefinitionRegistry(registry);registryProcessors.add(registryProcessor);}else {regularPostProcessors.add(postProcessor);}}

以：ConfigurationClassPostProcessor为例，实现了接口

BeanDefinitionRegistryPostProcessor继承自：BeanFactoryPostProcessor。

提供了：

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;}

重写了接口方法：

	public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {int registryId = System.identityHashCode(registry);if (this.registriesPostProcessed.contains(registryId)) {throw new IllegalStateException("postProcessBeanDefinitionRegistry already called on this post-processor against " + registry);}if (this.factoriesPostProcessed.contains(registryId)) {throw new IllegalStateException("postProcessBeanFactory already called on this post-processor against " + registry);}this.registriesPostProcessed.add(registryId);processConfigBeanDefinitions(registry);}

//解析配置类
protected final void parse(AnnotationMetadata metadata, String beanName) throws IOException {processConfigurationClass(new ConfigurationClass(metadata, beanName), DEFAULT_EXCLUSION_FILTER);
}

执行解析配置类

	protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass, Predicate filter)throws IOException

 扩展：spring的  import就是从这里解析的：

核心接口：

public interface ImportSelector {/*** 根据导入 @Configuration 类的 选择并返回应导入AnnotationMetadata的类的名称*/String[] selectImports(AnnotationMetadata importingClassMetadata);}

// 处理 @Import 注解
processImports(configClass, sourceClass, getImports(sourceClass), filter, true);

//循环import导入的类				
for (SourceClass candidate : importCandidates) {if (candidate.isAssignable(ImportSelector.class)) {// Candidate class is an ImportSelector -> delegate to it to determine importsClass candidateClass = candidate.loadClass();ImportSelector selector = ParserStrategyUtils.instantiateClass(candidateClass, ImportSelector.class,this.environment, this.resourceLoader, this.registry);Predicate selectorFilter = selector.getExclusionFilter();if (selectorFilter != null) {exclusionFilter = exclusionFilter.or(selectorFilter);}if (selector instanceof DeferredImportSelector) {this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);}else {
//处理实现了接口：ImportSelector的接口String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());Collection importSourceClasses = asSourceClasses(importClassNames, exclusionFilter);processImports(configClass, currentSourceClass, importSourceClasses, exclusionFilter, false);}}

以事务导入为例：AdviceModeImportSelector 实现了接口ImportSelector，重写了selectImports 方法，导入了其余的配置类：TransactionManagementConfigurationSelector

	protected String[] selectImports(AdviceMode adviceMode) {switch (adviceMode) {case PROXY:return new String[] {AutoProxyRegistrar.class.getName(),ProxyTransactionManagementConfiguration.class.getName()};case ASPECTJ:return new String[] {determineTransactionAspectClass()};default:return null;}}