spring源码分析系列 (2) spring拓展接口BeanPostProcessor

Spring更多分析--spring源码分析系列

主要分析内容：

一、BeanPostProcessor简述与demo示例

二、BeanPostProcessor源码分析：注册时机和触发点

(源码基于spring 5.1.3.RELEASE分析)

一、BeanPostProcessor简述与demo示例

BeanPostProcessor是spring非常重要的拓展接口，例如aop通过拓展接口生产代理bean等。接口有两个方法：

/**
 * Factory hook that allows for custom modification of new bean instances,
 * e.g. checking for marker interfaces or wrapping them with proxies.
 *
 * <p>ApplicationContexts can autodetect BeanPostProcessor beans in their
 * bean definitions and apply them to any beans subsequently created.
 * Plain bean factories allow for programmatic registration of post-processors,
 * applying to all beans created through this factory.
 *
 * <p>Typically, post-processors that populate beans via marker interfaces
 * or the like will implement {@link #postProcessBeforeInitialization},
 * while post-processors that wrap beans with proxies will normally
 * implement {@link #postProcessAfterInitialization}.
 *
 * @author Juergen Hoeller
 * @since 10.10.2003
 * @see InstantiationAwareBeanPostProcessor
 * @see DestructionAwareBeanPostProcessor
 * @see ConfigurableBeanFactory#addBeanPostProcessor
 * @see BeanFactoryPostProcessor
 */
public interface BeanPostProcessor {

    /**
     * Apply this BeanPostProcessor to the given new bean instance <i>before</i> any bean
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>The default implementation returns the given {@code bean} as-is.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one;
     * if {@code null}, no subsequent BeanPostProcessors will be invoked
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     */
    @Nullable
    default Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

    /**
     * Apply this BeanPostProcessor to the given new bean instance <i>after</i> any bean
     * initialization callbacks (like InitializingBean's {@code afterPropertiesSet}
     * or a custom init-method). The bean will already be populated with property values.
     * The returned bean instance may be a wrapper around the original.
     * <p>In case of a FactoryBean, this callback will be invoked for both the FactoryBean
     * instance and the objects created by the FactoryBean (as of Spring 2.0). The
     * post-processor can decide whether to apply to either the FactoryBean or created
     * objects or both through corresponding {@code bean instanceof FactoryBean} checks.
     * <p>This callback will also be invoked after a short-circuiting triggered by a
     * {@link InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation} method,
     * in contrast to all other BeanPostProcessor callbacks.
     * <p>The default implementation returns the given {@code bean} as-is.
     * @param bean the new bean instance
     * @param beanName the name of the bean
     * @return the bean instance to use, either the original or a wrapped one;
     * if {@code null}, no subsequent BeanPostProcessors will be invoked
     * @throws org.springframework.beans.BeansException in case of errors
     * @see org.springframework.beans.factory.InitializingBean#afterPropertiesSet
     * @see org.springframework.beans.factory.FactoryBean
     */
    @Nullable
    default Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        return bean;
    }

}

以上为spring原始接口，这里说明一下：

1. ApplicationContext类型的容器会自动发现和注册该类型的bean，通过BeanPostProcessor可以对bean进行定制化，接口作用域是所有bean创建。
2. postProcessBeforeInitialization触发时机在bean实例化(Instantiation)之后，所有初始化(Initialization)动作(包括 InitializingBean#afterPrpertiesSet() 和 定制化init-method())以前。
3. postProcessAfterInitialization触发时机在bean实例化(Instantiation)之后，所有初始化(Initialization)动作(包括 InitializingBean#afterPrpertiesSet() 和 定制化init-method())以后。同时还会在InstantiationAwareBeanPostProcessor#postProcessBeforeInstantiation 和 FactoryBean(bean工厂)获得bean时候调用。这个也是重要的点，放在往后的博客中阐述。

由于ApplicationContext可以自动发现并注册BeanPostProcessor，如下使用ApplicationContext类型容器实现一个简单demo。 对应的demo代码可参考： https://gitee.com/zhouxiaoxing91/learning-src/tree/master

 public class BeanPostProcessorTest {

     private ApplicationContext applicationContext ;

     @Before
     public void beforeApplicationContext(){
         /**
          * ApplicationContext 自动注册 BeanPostProcessor
          *  不需要手动注册
          * */
         applicationContext = new ClassPathXmlApplicationContext("ioc-beanPostProcessor.xml") ;
     }

     @Test
     public void test(){
         Bean bean = applicationContext.getBean("bean", Bean.class) ;
         System.out.println(bean);
     }

     @After
     public void after(){
         ((ClassPathXmlApplicationContext)applicationContext).close();
     }
 }

BeanPostProcessorTest.java

 public class Bean {

     public Bean(){

     }

     public Bean(String name){
         System.out.println("构造函数被调用啦");
         this.name = name ;
     }

     private String name ;

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     @Override
     public String toString() {
         return "Bean{" +
                 "name='" + name + '\'' +
                 '}';
     }
 }

Bean.java

 public class LogicBeanPostProcessor implements BeanPostProcessor {

     @Nullable
     @Override
     public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
         System.out.println("LogicBeanPostProcessor.postProcessAfterInitialization 执行啦 beanName = " + beanName);
         return bean;
     }

     @Nullable
     @Override
     public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
         System.out.println("LogicBeanPostProcessor.postProcessBeforeInitialization 执行啦 beanName = " + beanName);
         return bean;
     }
 }

LogicBeanPostProcessor.java

 <?xml version="1.0" encoding="utf-8"?>
 <beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"
        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

     <bean id="bean" class="com.nancy.ioc.Bean">
         <constructor-arg name="name" value="zhouxiaoxing"/>
     </bean>

     <bean id="logicBeanPostProcessor" class="com.nancy.ioc.BeanPostProcessor.LogicBeanPostProcessor"/>
 </beans>

ioc-beanPostProcessor.xml

运行结果符合以上的结论：

构造函数被调用啦
LogicBeanPostProcessor.postProcessBeforeInitialization 执行啦 beanName = bean
LogicBeanPostProcessor.postProcessAfterInitialization 执行啦 beanName = bean
Bean{name='zhouxiaoxing'}

提出两个疑问：

1、在ApplicationContext容器中何时注册BeanPostProcessor接口 ？

2、何时apply对应的回调方法呢 ？

二、BeanPostProcessor源码分析：注册时机和触发点

1、注册BeanPostProcessor

在AbstractApplicationContext容器启动的refresh()会注册BeanPostProcessor，源码如下：

 @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 {
                 // Allows post-processing of the bean factory in context subclasses.
                 postProcessBeanFactory(beanFactory);

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

                 // Register bean processors that intercept bean creation.
                 // 注册BeanPostProcessor 在bean创建的时候进行拦截
                registerBeanPostProcessors(beanFactory);

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

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

                 // Initialize other special beans in specific context subclasses.
                 onRefresh();

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

                 // Instantiate all remaining (non-lazy-init) singletons.
                 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 BeanPostProcessor beans,
      * respecting explicit order if given.
      * <p>Must be called before any instantiation of application beans.
      */
     protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
         PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
     }

跟进PostProcessorRegistrationDelegate.registerBeanPostProcessors

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

         /**
          * 此时bean的定义加载已经完成，但是还没有实例化。 获得所有BeanPostProcessor bean对应的beanName
          */
         String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

         /**
          * 注册日志BeanPostProcessor， 检测注册的bean是否为spring基础服务类并打印日志
          */
         // Register BeanPostProcessorChecker that logs an info message when
         // a bean is created during BeanPostProcessor instantiation, i.e. when
         // a bean is not eligible for getting processed by all BeanPostProcessors.
         int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
         beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));

         /**
          * 当有注册多个BeanPostProcessor接口时会按顺序进行，即 实现PriorityOrdered->实现Ordered->普通类型接口->内部系统MergedBeanDefinitionPostProcessor
          */
         // Separate between BeanPostProcessors that implement PriorityOrdered,
         // Ordered, and the rest.
         List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
         List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
         List<String> orderedPostProcessorNames = new ArrayList<>();
         List<String> nonOrderedPostProcessorNames = new ArrayList<>();
         for (String ppName : postProcessorNames) {
             if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {

                /**
                  * 通过beanFactory.getBean(), 将会提前初始化BeanPostProcessor类型实例
                  */
                 BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
                 priorityOrderedPostProcessors.add(pp);
                 if (pp instanceof MergedBeanDefinitionPostProcessor) {
                     internalPostProcessors.add(pp);
                 }
             }
             else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
                 orderedPostProcessorNames.add(ppName);
             }
             else {
                 nonOrderedPostProcessorNames.add(ppName);
             }
         }

         // First, register the BeanPostProcessors that implement PriorityOrdered.
         sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
         registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

         // Next, register the BeanPostProcessors that implement Ordered.
         List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>();
         for (String ppName : orderedPostProcessorNames) {
             BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
             orderedPostProcessors.add(pp);
             if (pp instanceof MergedBeanDefinitionPostProcessor) {
                 internalPostProcessors.add(pp);
             }
         }
         sortPostProcessors(orderedPostProcessors, beanFactory);
         registerBeanPostProcessors(beanFactory, orderedPostProcessors);

         // Now, register all regular BeanPostProcessors.
         List<BeanPostProcessor> nonOrderedPostProcessors = new ArrayList<>();
         for (String ppName : nonOrderedPostProcessorNames) {
             BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
             nonOrderedPostProcessors.add(pp);
             if (pp instanceof MergedBeanDefinitionPostProcessor) {
                 internalPostProcessors.add(pp);
             }
         }
         registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);

         // Finally, re-register all internal BeanPostProcessors.
         sortPostProcessors(internalPostProcessors, beanFactory);
         registerBeanPostProcessors(beanFactory, internalPostProcessors);

         /**
          * ApplicationListener探测器，当bean实现ApplicationListener接口时自动注册监听
          */
         // Re-register post-processor for detecting inner beans as ApplicationListeners,
         // moving it to the end of the processor chain (for picking up proxies etc).
         beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
     }

     /**
      * 按照给定Ordered的顺序排序
      */
     private static void sortPostProcessors(List<?> postProcessors, ConfigurableListableBeanFactory beanFactory) {
         Comparator<Object> comparatorToUse = null;
         if (beanFactory instanceof DefaultListableBeanFactory) {
             comparatorToUse = ((DefaultListableBeanFactory) beanFactory).getDependencyComparator();
         }
         if (comparatorToUse == null) {
             comparatorToUse = OrderComparator.INSTANCE;
         }
         postProcessors.sort(comparatorToUse);
     }

     /**
      * Register the given BeanPostProcessor beans.
      */
     private static void registerBeanPostProcessors(
             ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {

         for (BeanPostProcessor postProcessor : postProcessors) {
             beanFactory.addBeanPostProcessor(postProcessor);
         }
     }

跟进AbstractBeanFactory#addBeanPostProcessor

     /** BeanPostProcessors to apply in createBean. */
     private final List<BeanPostProcessor> beanPostProcessors = new CopyOnWriteArrayList<>();

     /** Indicates whether any InstantiationAwareBeanPostProcessors have been registered. */
     private volatile boolean hasInstantiationAwareBeanPostProcessors;

     /** Indicates whether any DestructionAwareBeanPostProcessors have been registered. */
     private volatile boolean hasDestructionAwareBeanPostProcessors;

     /**
      * 所有的BeanPostProcessor接口实例保存于CopyOnWriteArrayList中
      * 1、一个实例只注册一次
      * 2、通过hasInstantiationAwareBeanPostProcessors设置，判定是否存在InstantiationAwareBeanPostProcessor接口实例，为后续执行做判断
      * 3、通过hasDestructionAwareBeanPostProcessors设置，判定是否存在DestructionAwareBeanPostProcessor接口实例，为后续执行做判断
      */
     @Override
     public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
         Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
         // Remove from old position, if any
         this.beanPostProcessors.remove(beanPostProcessor);
         // Track whether it is instantiation/destruction aware
         if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
             this.hasInstantiationAwareBeanPostProcessors = true;
         }
         if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
             this.hasDestructionAwareBeanPostProcessors = true;
         }
         // Add to end of list
         this.beanPostProcessors.add(beanPostProcessor);
     }

修改上述demo中LogicBeanPostProcessor.java文件，并debug模式查看：

 public class LogicBeanPostProcessor implements BeanPostProcessor {

     public LogicBeanPostProcessor(){
         System.out.println("LogicBeanPostProcessor 被 beanFactory.getBean() 提前初始化");
     }

     @Nullable
     @Override
     public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
         System.out.println("LogicBeanPostProcessor.postProcessAfterInitialization 执行啦 beanName = " + beanName);
         return bean;
     }

     @Nullable
     @Override
     public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
         System.out.println("LogicBeanPostProcessor.postProcessBeforeInitialization 执行啦 beanName = " + beanName);
         return bean;
     }
 }

查看PostProcessorRegistrationDelegate#registerBeanPostProcessors，注册一个普通BeanPostProcessor ->  logicBeanPostProcessor

最后运行结果：

LogicBeanPostProcessor 被 beanFactory.getBean() 提前初始化
构造函数被调用啦
LogicBeanPostProcessor.postProcessBeforeInitialization 执行啦 beanName = bean
LogicBeanPostProcessor.postProcessAfterInitialization 执行啦 beanName = bean
Bean{name='zhouxiaoxing'}

总结如下：

(1)、BeanPostProcessor注册的入口在AbstractApplicationContext容器启动的refresh()的AbstractApplicationContext#registerBeanPostProcessors。

(2)、AbstractApplicationContext进而委派PostProcessorRegistrationDelegate#registerBeanPostProcessors实现注册。

(3)、当有注册多个BeanPostProcessor接口时会按顺序进行，即 实现PriorityOrdered->实现Ordered->普通类型接口->内部系统MergedBeanDefinitionPostProcessor。而同种类型也会进行排序，按顺序注册。

(4)、BeanPostProcessor类型实例会通过BeanFactory#getBean()提前初始化。

2、触发BeanPostProcessor方法

触发BeanPostProcessor有很多入口，首先分析几个入口后续的再补上。

触发（1）AbstractAutowireCapableBeanFactory#createBean 中：

    /**
      * Central method of this class: creates a bean instance,
      * populates the bean instance, applies post-processors, etc.
      * @see #doCreateBean
      */
     @Override
     protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
             throws BeanCreationException {

         if (logger.isTraceEnabled()) {
             logger.trace("Creating instance of bean '" + beanName + "'");
         }
         RootBeanDefinition mbdToUse = mbd;

         // Make sure bean class is actually resolved at this point, and
         // clone the bean definition in case of a dynamically resolved Class
         // which cannot be stored in the shared merged bean definition.
         Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
         if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
             mbdToUse = new RootBeanDefinition(mbd);
             mbdToUse.setBeanClass(resolvedClass);
         }

         // Prepare method overrides.
         try {
             mbdToUse.prepareMethodOverrides();
         }
         catch (BeanDefinitionValidationException ex) {
             throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                     beanName, "Validation of method overrides failed", ex);
         }

         try {
             // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
             Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
             if (bean != null) {
                 return bean;
             }
         }
         catch (Throwable ex) {
             throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                     "BeanPostProcessor before instantiation of bean failed", ex);
         }

         try {
             // bean 创建
             Object beanInstance = doCreateBean(beanName, mbdToUse, args);
             if (logger.isTraceEnabled()) {
                 logger.trace("Finished creating instance of bean '" + beanName + "'");
             }
             return beanInstance;
         }
         catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
             // A previously detected exception with proper bean creation context already,
             // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
             throw ex;
         }
         catch (Throwable ex) {
             throw new BeanCreationException(
                     mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
         }
     }

     /**
      * Actually create the specified bean. Pre-creation processing has already happened
      * at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks.
      * <p>Differentiates between default bean instantiation, use of a
      * factory method, and autowiring a constructor.
      * @param beanName the name of the bean
      * @param mbd the merged bean definition for the bean
      * @param args explicit arguments to use for constructor or factory method invocation
      * @return a new instance of the bean
      * @throws BeanCreationException if the bean could not be created
      * @see #instantiateBean
      * @see #instantiateUsingFactoryMethod
      * @see #autowireConstructor
      */
     protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
             throws BeanCreationException {

         // Instantiate the bean.
         BeanWrapper instanceWrapper = null;
         if (mbd.isSingleton()) {
             instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
         }
         if (instanceWrapper == null) {
             instanceWrapper = createBeanInstance(beanName, mbd, args);
         }

         // 省略...... 

         // Initialize the bean instance.
         Object exposedObject = bean;
         try {
             // 根据加载到的bean definition给 bean赋值
             populateBean(beanName, mbd, instanceWrapper);
             // 调用bean初始化方法
             exposedObject = initializeBean(beanName, exposedObject, mbd);
         }
         catch (Throwable ex) {
             if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
                 throw (BeanCreationException) ex;
             }
             else {
                 throw new BeanCreationException(
                         mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
             }
         }

         // 省略...... 

         return exposedObject;
     }

跟进AbstractAutowireCapableBeanFactory#initializeBean方法：

 /**
      * Initialize the given bean instance, applying factory callbacks
      * as well as init methods and bean post processors.
      * <p>Called from {@link #createBean} for traditionally defined beans,
      * and from {@link #initializeBean} for existing bean instances.
      * @param beanName the bean name in the factory (for debugging purposes)
      * @param bean the new bean instance we may need to initialize
      * @param mbd the bean definition that the bean was created with
      * (can also be {@code null}, if given an existing bean instance)
      * @return the initialized bean instance (potentially wrapped)
      * @see BeanNameAware
      * @see BeanClassLoaderAware
      * @see BeanFactoryAware
      * @see #applyBeanPostProcessorsBeforeInitialization
      * @see #invokeInitMethods
      * @see #applyBeanPostProcessorsAfterInitialization
      */
     protected Object initializeBean(final String beanName, final Object bean, @Nullable RootBeanDefinition mbd) {
         // 1、工厂factory类 接口回调  
         if (System.getSecurityManager() != null) {
             AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
                 invokeAwareMethods(beanName, bean);
                 return null;
             }, getAccessControlContext());
         }
         else {
             invokeAwareMethods(beanName, bean);
         }

         Object wrappedBean = bean;
         if (mbd == null || !mbd.isSynthetic()) {
             // 2、BeanPostProcessor前置执行
             wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
         }

         try {
             // 3、InitializingBean接口方法 or 自定义 init method 执行
             invokeInitMethods(beanName, wrappedBean, mbd);
         }
         catch (Throwable ex) {
             throw new BeanCreationException(
                     (mbd != null ? mbd.getResourceDescription() : null),
                     beanName, "Invocation of init method failed", ex);
         }
         if (mbd == null || !mbd.isSynthetic()) {
             // 4、BeanPostProcessor后置执行
             wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
         }

         return wrappedBean;
     }

对应回调方法：

 private void invokeAwareMethods(final String beanName, final Object bean) {
         if (bean instanceof Aware) {
             if (bean instanceof BeanNameAware) {
                 ((BeanNameAware) bean).setBeanName(beanName);
             }
             if (bean instanceof BeanClassLoaderAware) {
                 ClassLoader bcl = getBeanClassLoader();
                 if (bcl != null) {
                     ((BeanClassLoaderAware) bean).setBeanClassLoader(bcl);
                 }
             }
             if (bean instanceof BeanFactoryAware) {
                 ((BeanFactoryAware) bean).setBeanFactory(AbstractAutowireCapableBeanFactory.this);
             }
         }
     }

     /**
      * Give a bean a chance to react now all its properties are set,
      * and a chance to know about its owning bean factory (this object).
      * This means checking whether the bean implements InitializingBean or defines
      * a custom init method, and invoking the necessary callback(s) if it does.
      * @param beanName the bean name in the factory (for debugging purposes)
      * @param bean the new bean instance we may need to initialize
      * @param mbd the merged bean definition that the bean was created with
      * (can also be {@code null}, if given an existing bean instance)
      * @throws Throwable if thrown by init methods or by the invocation process
      * @see #invokeCustomInitMethod
      */
     protected void invokeInitMethods(String beanName, final Object bean, @Nullable RootBeanDefinition mbd)
             throws Throwable {

         boolean isInitializingBean = (bean instanceof InitializingBean);
         if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
             if (logger.isTraceEnabled()) {
                 logger.trace("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
             }
             if (System.getSecurityManager() != null) {
                 try {
                     AccessController.doPrivileged((PrivilegedExceptionAction<Object>) () -> {
                         ((InitializingBean) bean).afterPropertiesSet();
                         return null;
                     }, getAccessControlContext());
                 }
                 catch (PrivilegedActionException pae) {
                     throw pae.getException();
                 }
             }
             else {
                 ((InitializingBean) bean).afterPropertiesSet();
             }
         }

         if (mbd != null && bean.getClass() != NullBean.class) {
             String initMethodName = mbd.getInitMethodName();
             if (StringUtils.hasLength(initMethodName) &&
                     !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                     !mbd.isExternallyManagedInitMethod(initMethodName)) {
                 invokeCustomInitMethod(beanName, bean, mbd);
             }
         }
     }

     @Override
     public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
             throws BeansException {

         Object result = existingBean;
         for (BeanPostProcessor processor : getBeanPostProcessors()) {
             Object current = processor.postProcessBeforeInitialization(result, beanName);
             if (current == null) {
                 return result;
             }
             result = current;
         }
         return result;
     }

     @Override
     public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)
             throws BeansException {

         Object result = existingBean;
         for (BeanPostProcessor processor : getBeanPostProcessors()) {
             Object current = processor.postProcessAfterInitialization(result, beanName);
             if (current == null) {
                 return result;
             }
             result = current;
         }
         return result;
     }

initializeBean对应的方法

总结如下：

(1.1)、由此可见BeanPostProcessor的一个触发入口在AbstractAutowireCapableBeanFactory#createBean，最终至AbstractAutowireCapableBeanFactory#initializeBean。

(1.2)、AbstractAutowireCapableBeanFactory#initializeBean不但会触发BeanPostProcessor回掉方法，并且还会按顺序执行bean生命周期：

1. factory类型接口(BeanNameAware#setBeanName)
2. factory类型接口(BeanClassLoaderAware#setBeanClassLoader)
3. factory类型接口(BeanFactoryAware#setBeanFactory)
4. BeanPostProcessor#postProcessBeforeInitialization
5. InitializingBean和自定义的init-method
6. BeanPostProcessor#postProcessAfterInitialization

触发（2）FactoryBeanRegistrySupport（后续补上）