接着上文《spring源码阅读（2）-- 容器启动之加载BeanDefinition》，当spring加载完所有BeanDefinition时，并不会马上去创建bean，而是先配置beanFactory，例如设置一下装配规则和判断是否需要创建一些指定的bean。

1 　　protected voidprepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {2         //Tell the internal bean factory to use the context's class loader etc.
3 beanFactory.setBeanClassLoader(getClassLoader());4         beanFactory.setBeanExpressionResolver(newStandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));5         beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));6
7         //Configure the bean factory with context callbacks.8         //添加ApplicationContextAwareProcessor用于处理实现了EnvironmentAware、EmbeddedValueResolverAware、ApplicationContextAware接口的bean
9         beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));10         //忽略以下bean的依赖注入
11         beanFactory.ignoreDependencyInterface(ResourceLoaderAware.class);12         beanFactory.ignoreDependencyInterface(ApplicationEventPublisherAware.class);13         beanFactory.ignoreDependencyInterface(MessageSourceAware.class);14         beanFactory.ignoreDependencyInterface(ApplicationContextAware.class);15         beanFactory.ignoreDependencyInterface(EnvironmentAware.class);16
17         //BeanFactory interface not registered as resolvable type in a plain factory.18         //MessageSource registered (and found for autowiring) as a bean.19         //注册自动装配模式下的特殊依赖，例如被注入的是BeanFactory类型，那么注入的就是beanFactory
20         beanFactory.registerResolvableDependency(BeanFactory.class, beanFactory);21         beanFactory.registerResolvableDependency(ResourceLoader.class, this);22         beanFactory.registerResolvableDependency(ApplicationEventPublisher.class, this);23         beanFactory.registerResolvableDependency(ApplicationContext.class, this);24
25         //Detect a LoadTimeWeaver and prepare for weaving, if found.
26         if(beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {27             beanFactory.addBeanPostProcessor(newLoadTimeWeaverAwareProcessor(beanFactory));28             //Set a temporary ClassLoader for type matching.
29             beanFactory.setTempClassLoader(newContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));30 }31
32         //Register default environment beans.
33         if (!beanFactory.containsLocalBean(ENVIRONMENT_BEAN_NAME)) {34 beanFactory.registerSingleton(ENVIRONMENT_BEAN_NAME, getEnvironment());35 }36         if (!beanFactory.containsLocalBean(SYSTEM_PROPERTIES_BEAN_NAME)) {37 beanFactory.registerSingleton(SYSTEM_PROPERTIES_BEAN_NAME, getEnvironment().getSystemProperties());38 }39         if (!beanFactory.containsLocalBean(SYSTEM_ENVIRONMENT_BEAN_NAME)) {40 beanFactory.registerSingleton(SYSTEM_ENVIRONMENT_BEAN_NAME, getEnvironment().getSystemEnvironment());41 }42     }

　　当设置完beanFactory，接下来就是执行BeanFactoryPostProcessor。BeanFactoryPostProcessor是spring容器启动时暴露给用户的一个扩展点，允许用户在spring创建bean之前做修改或动态添加bean，动态注册bean可以使用BeanFactoryPostProcessor的子类BeanDefinitionRegistryPostProcessor。BeanFactoryPostProcessor接口定义如下：

1  public interfaceBeanFactoryPostProcessor {2
3     void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throwsBeansException;4
5 }

　　当我们实现了BeanFactoryPostProcessor，spring是怎么去执行的呢？

　　spring容器在执行刷新时，当加载完BeanDefinition和配置好beanFactory时，会进入AbstractApplicationContext.invokeBeanFactoryPostProcessors，方法里首先调用PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors去执行实现了BeanFactoryPostProcessor的postProcessBeanFactory方法，然后再判断是否新添加了loadTimeWeaver这个bean，如果有，添加LoadTimeWeaverAwareProcessor

1     protected voidinvokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {2 PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());3
4         //Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime5         //(e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
6         if (beanFactory.getTempClassLoader() == null &&beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {7             beanFactory.addBeanPostProcessor(newLoadTimeWeaverAwareProcessor(beanFactory));8             beanFactory.setTempClassLoader(newContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));9 }10     }

　　进入PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors方法，方法里首先判断beanFactory是不是一个bean注册中心，如果是，循环遍历传入的BeanFactoryPostProcessor，判断是否是BeanDefinitionRegistryPostProcessor的实现，如果是，执行BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry，然后保存到一个集合用于在执行完所有的BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry方法之后，再执行BeanFactoryPostProcessor.postProcessBeanFactory。

1     public static voidinvokeBeanFactoryPostProcessors(2             ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor>beanFactoryPostProcessors) {3
4         //Invoke BeanDefinitionRegistryPostProcessors first, if any.
5         Set<String> processedBeans = new HashSet<String>();6
7         if (beanFactory instanceofBeanDefinitionRegistry) {8             BeanDefinitionRegistry registry =(BeanDefinitionRegistry) beanFactory;9             List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();10             List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
11                     new LinkedList<BeanDefinitionRegistryPostProcessor>();12
13             for(BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {14                 if (postProcessor instanceofBeanDefinitionRegistryPostProcessor) {15                     BeanDefinitionRegistryPostProcessor registryPostProcessor =
16 (BeanDefinitionRegistryPostProcessor) postProcessor;17 registryPostProcessor.postProcessBeanDefinitionRegistry(registry);18 registryPostProcessors.add(registryPostProcessor);19 }20                 else{21 regularPostProcessors.add(postProcessor);22 }23 }24
25             //Do not initialize FactoryBeans here: We need to leave all regular beans26             //uninitialized to let the bean factory post-processors apply to them!27             //Separate between BeanDefinitionRegistryPostProcessors that implement28             //PriorityOrdered, Ordered, and the rest.
29             String[] postProcessorNames =
30                     beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);31
32             //First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
33             List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();34             for(String ppName : postProcessorNames) {35                 if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {36                     priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));37 processedBeans.add(ppName);38 }39 }40 sortPostProcessors(beanFactory, priorityOrderedPostProcessors);41 registryPostProcessors.addAll(priorityOrderedPostProcessors);42 invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);43
44             //Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
45             postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);46             List<BeanDefinitionRegistryPostProcessor> orderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();47             for(String ppName : postProcessorNames) {48                 if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {49                     orderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));50 processedBeans.add(ppName);51 }52 }53 sortPostProcessors(beanFactory, orderedPostProcessors);54 registryPostProcessors.addAll(orderedPostProcessors);55 invokeBeanDefinitionRegistryPostProcessors(orderedPostProcessors, registry);56
57             //Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
58             boolean reiterate = true;59             while(reiterate) {60                 reiterate = false;61                 postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);62                 for(String ppName : postProcessorNames) {63                     if (!processedBeans.contains(ppName)) {64                         BeanDefinitionRegistryPostProcessor pp = beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class);65 registryPostProcessors.add(pp);66 processedBeans.add(ppName);67 pp.postProcessBeanDefinitionRegistry(registry);68                         reiterate = true;69 }70 }71 }72
73             //Now, invoke the postProcessBeanFactory callback of all processors handled so far.
74 invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);75 invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);76 }77
78         else{79             //Invoke factory processors registered with the context instance.
80 invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);81 }82
83         //Do not initialize FactoryBeans here: We need to leave all regular beans84         //uninitialized to let the bean factory post-processors apply to them!
85         String[] postProcessorNames =
86                 beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);87
88         //Separate between BeanFactoryPostProcessors that implement PriorityOrdered,89         //Ordered, and the rest.
90         List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();91         List<String> orderedPostProcessorNames = new ArrayList<String>();92         List<String> nonOrderedPostProcessorNames = new ArrayList<String>();93         for(String ppName : postProcessorNames) {94             if(processedBeans.contains(ppName)) {95                 //skip - already processed in first phase above
96 }97             else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {98                 priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));99 }100             else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {101 orderedPostProcessorNames.add(ppName);102 }103             else{104 nonOrderedPostProcessorNames.add(ppName);105 }106 }107
108         //First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
109 sortPostProcessors(beanFactory, priorityOrderedPostProcessors);110 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);111
112         //Next, invoke the BeanFactoryPostProcessors that implement Ordered.
113         List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();114         for(String postProcessorName : orderedPostProcessorNames) {115             orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));116 }117 sortPostProcessors(beanFactory, orderedPostProcessors);118 invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);119
120         //Finally, invoke all other BeanFactoryPostProcessors.
121         List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();122         for(String postProcessorName : nonOrderedPostProcessorNames) {123             nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));124 }125 invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);126
127         //Clear cached merged bean definitions since the post-processors might have128         //modified the original metadata, e.g. replacing placeholders in values...
129 beanFactory.clearMetadataCache();130     }

　　invokeBeanFactoryPostProcessors方法里会找出所有的bean，先排序然后再执行相应的方法。从源码可以看得出，先执行的是传进来的BeanFactoryPostProcessor，第二是实现了PriorityOrdered的接口，第三是实现了Ordered接口，最后的就是没有指定顺序的，而实现了BeanDefinitionRegistryPostProcessor的，会先执行BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry。

　　至此，spring对BeanFactoryPostProcessor的扩展点已处理完，从源码可以开出，BeanFactoryPostProcessor的处理会触发bean的创建。