体系全能软件测试工程师内含资料

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Spring5源码5-Bean生命周期后置处理器

主要说明三种生命周期增强器：

BeanFactoryPostProcessor:BeanFactory 后置处理器

BeanDefinitionRegistryPostProcessor：bean定义注册后置处理器
BeanFactoryPostProcessor
BeanPostProcessor:Bean后置处理器

BeanPostProcessor
MergedBeanDefinitionPostProcessor
SmartInstantiationAwareBeanPostProcessor
InstantiationAwareBeanPostProcessor
InitializingBean

DisposableBean (销毁的方案我们暂时不做说明)

1.1 什么是 BeanPostProcessor
BeanPostProcessor 是 Spring提供给我们的一个非常重要的扩展接口，并且Spring内部的很多功能也是通过 BeanPostProcessor 来完成的(目前看到最典型的就是 AnnotationAwareAspectJAutoProxyCreator 的注入)。

1.2 BeanPostProcessor 的种类
BeanPostProcessor 在Spring 中的子类非常多(idea 显是有46个)，比如

InstantiationAwareBeanPostProcessorAdapter ：在Spring 的bean加载过程中起了非常重要的作用
AnnotationAwareAspectJAutoProxyCreator ： bean 创建过程中的属性注入时起作用
AspectJAwareAdvisorAutoProxyCreator ： Aspect 的 AOP 功能实现也全仰仗BeanPostProcessor 的特性。
1.3 创建时机
BeanFactoryPostProcessor：在 Spring 启动时对BeanDefinition 的创建进行干预处理。

BeanPostProcessor:一是Bean对应的BeanDefinition 的创建。二是Bean 实例的创建。因为在 Spring容器中，Bean的创建并非仅仅通过反射创建就结束了，在创建过程中，需要考虑到Bean针对Spring容器中的一些属性，所以BeanDefinition 中不仅仅包含了 Bean Class 文件信息，还包含了当前Bean在Spring容器中的一些属性，比如在容器中的作用域、是否懒加载、别名等信息。当Bean 进行实例化创建时需要依赖于对应的BeanDefinition 提供对应的信息。。

而由于 BeanPostProcessor 是参与了 Bean 创建过程。所以其创建一定在普通 Bean 之前。实际上 BeanPostProcessor 的创建时在 Spring 启动时容器刷新的时候。

BeanPostProcessor 的 BeanDefinition 创建时机和普通 Bean没有区别，都是在Spring 启动时的BeanFactoryPostProcessor 中完成(确切的说是 ConfigurationClassPostProcessor 中完成)。

而BeanPostProcessor 的实例创建要优先于普通bean创建，Spring启动过程中会调用AbstractApplicationContext#registerBeanPostProcessors 方法。在这个方法中，Spring 会从容器中获取到所有BeanPostProcessor 类型的beanName，通过 beanFactory.getBean 方法获取到对应实例，进行排序后注册到 BeanFactory.beanPostProcessors 属性中.当容器需要执行 BeanPostProcessor 方法时可以直接从 beanPostProcessors 中获取即可。

案例
分别定义几个测试类，实现bean的后置处理器：

BeanDefinitionRegistryPostProcessor:

/**

BeanFactory的后置处理器 , PriorityOrdered, Ordered
*/

@Component
public class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
public MyBeanDefinitionRegistryPostProcessor(){

  System.out.println("MyBeanDefinitionRegistryPostProcessor");

}

@Override //紧接着执行
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

  System.out.println("MyBeanDefinitionRegistryPostProcessor....postProcessBeanFactory...");

}

@Override //先执行的
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {

  System.out.println("MyBeanDefinitionRegistryPostProcessor...postProcessBeanDefinitionRegistry...");
  //增强bean定义信息的注册中心，比如自己注册组件

}
}
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BeanFactoryPostProcessor:

/**

BeanFactory的后置处理器
*/

@Component
public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

public MyBeanFactoryPostProcessor(){

  System.out.println("MyBeanFactoryPostProcessor...");

}

@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {

  System.out.println("BeanFactoryPostProcessor....postProcessBeanFactory==>"+beanFactory);

}
}
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BeanPostProcessor:

/**

Bean组件的 PostProcessor；
*/

@Component
public class MyBeanPostProcessor implements BeanPostProcessor {

public MyBeanPostProcessor(){

  System.out.println("MyBeanPostProcessor...");

}

public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

  System.out.println("MyBeanPostProcessor...postProcessAfterInitialization..."+bean+"==>"+beanName);
  return bean;

}

public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

  System.out.println("MyBeanPostProcessor...postProcessBeforeInitialization..."+bean+"==>"+beanName);
  return bean; // new Object();

}
}
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InstantiationAwareBeanPostProcessor:

@Component
public class MyInstantiationAwareBeanPostProcessor implements InstantiationAwareBeanPostProcessor {

public MyInstantiationAwareBeanPostProcessor(){

  System.out.println("MyInstantiationAwareBeanPostProcessor...");

}

//初始化之前进行后置处理，Spring留给我们给这个组件创建对象的回调。
public Object postProcessBeforeInstantiation(Class beanClass, String beanName) throws BeansException {

  System.out.println("MyInstantiationAwareBeanPostProcessor...postProcessBeforeInstantiation=>"+beanClass+"--"+beanName);
  //if(class.isAssFrom(Cat.class)){return new Dog()}
  //如果我们自己创建了对象返回。Spring则不会帮我们创建对象，用我们自己创建的对象？ 我们创建的这个对象，Spring会保存单实例？还是每次getBean都调到我们这里创建一个新的？
  return null;

}

// 是否让剩下的后置处理器对bean继续进行处理
public boolean postProcessAfterInstantiation(Object bean, String beanName) throws BeansException {

  //提前改变一些Spring不管的bean里面的属性
  System.out.println("MyInstantiationAwareBeanPostProcessor...postProcessAfterInstantiation=>"+bean+"--"+beanName);
  return true; //返回false则bean的赋值全部结束

}
//解析自定义注解进行属性值注入；pvs 封装了所有的属性信息。
public PropertyValues postProcessProperties(PropertyValues pvs, Object bean, String beanName)

     throws BeansException { //@GuiguValue();redis
  System.out.println("MyInstantiationAwareBeanPostProcessor...postProcessProperties=>"+bean+"--"+beanName);
  return null;

}

// public PropertyValues postProcessPropertyValues(
// PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
// System.out.println("MyInstantiationAwareBeanPostProcessor...postProcessProperties");
// return pvs;
// }
}
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MergedBeanDefinitionPostProcessor:

@Component
public class MyMergedBeanDefinitionPostProcessor implements MergedBeanDefinitionPostProcessor {

public MyMergedBeanDefinitionPostProcessor(){

  System.out.println("MyMergedBeanDefinitionPostProcessor...");

}

@Override
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {

  System.out.println("MyMergedBeanDefinitionPostProcessor...postProcessBeforeInitialization...=>"+bean+"--"+beanName);
  return bean; //null

}

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

  System.out.println("MyMergedBeanDefinitionPostProcessor...postProcessAfterInitialization..=>"+bean+"--"+beanName);
  return null;

}

@Override
public void postProcessMergedBeanDefinition(RootBeanDefinition beanDefinition, Class beanType, String beanName) {

  System.out.println("MyMergedBeanDefinitionPostProcessor...postProcessMergedBeanDefinition..=>"+beanName+"--"+beanType+"---"+beanDefinition);

}

@Override
public void resetBeanDefinition(String beanName) {

  System.out.println("MyMergedBeanDefinitionPostProcessor...resetBeanDefinition.."+beanName);

}
}
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SmartInstantiationAwareBeanPostProcessor:

@Component //bean进行代理增强期间进行使用
public class MySmartInstantiationAwareBeanPostProcessor implements SmartInstantiationAwareBeanPostProcessor {

public MySmartInstantiationAwareBeanPostProcessor(){

  System.out.println("MySmartInstantiationAwareBeanPostProcessor...");

}

//预测bean的类型，最后一次改变组件类型。
public Class predictBeanType(Class beanClass, String beanName) throws BeansException {

  System.out.println("MySmartInstantiationAwareBeanPostProcessor...predictBeanType=>"+beanClass+"--"+beanName);
  return null;

}

//返回我们要使用的构造器候选列表

public Constructor[] determineCandidateConstructors(Class beanClass, String beanName) throws BeansException {

  System.out.println("MySmartInstantiationAwareBeanPostProcessor...determineCandidateConstructors=>"+beanClass+"--"+beanName);
  //返回一个我们指定的构造器
  return null;

}

 //返回早期的bean引用，定义三级缓存中的bean信息

public Object getEarlyBeanReference(Object bean, String beanName) throws BeansException {

  System.out.println("MySmartInstantiationAwareBeanPostProcessor...getEarlyBeanReference=>"+bean+"--"+beanName);

  return bean; //

}

}
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InitializingBean:

@Component
public class CatInitializingBean implements InitializingBean {

public CatInitializingBean(){

  System.out.println("cat被创建了...");

}

private String name;

@Value("${JAVA_HOME}") //自动赋值功能
public void setName(String name) {

  System.out.println("cat....setName正在赋值调用....");
  this.name = name;

}
//注解怎么定义这个是初始化方法？
public String getName() {

  return name;

}

@Override
public void afterPropertiesSet() throws Exception {

  System.out.println("CatInitializingBean..afterPropertiesSet...");

}

@Autowired
private void init() {

  System.out.println("CatInitializingBean init....");

}

}
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debug打点：在每个构造器和方法上都打上断点，主要看看每个方法的执行时机是什么时候？

源码分析
入口还是： org.springframework.context.support.AbstractApplicationContext#refresh：

// 容器刷新的十二大步骤
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {

  // 容器启动的状态
  StartupStep contextRefresh = this.applicationStartup.start("spring.context.refresh");

  // Prepare this context for refreshing.
  // 1.准备上下文环境
  prepareRefresh();

  // Tell the subclass to refresh the internal bean factory.
  /** 1、创建BeanFactory对象
  *  2、xml解析
  *  传统标签解析：bean、import等
  *  自定义标签解析 如：
  *  自定义标签解析流程：
  *     a、根据当前解析标签的头信息找到对应的namespaceUri
  *     b、加载spring所以jar中的spring.handlers文件。并建立映射关系
  *     c、根据namespaceUri从映射关系中找到对应的实现了NamespaceHandler接口的类
  *     d、调用类的init方法，init方法是注册了各种自定义标签的解析类
  *     e、根据namespaceUri找到对应的解析类，然后调用paser方法完成标签解析
  * 3、把解析出来的xml标签封装成BeanDefinition对象
  */
  // 2. 工厂创建：BeanFactory 第一次开始创建的时候，有xml解析逻辑
  ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

  // Prepare the bean factory for use in this context.
  // 3. 预准备工厂，给容器中注册了环境信息作为单实例Bean  方便后续自动装配
  // 并且放了一些后置处理器（监听、xxxAware功能）
  prepareBeanFactory(beanFactory);

  try {
     //  Allows post-processing of the bean factory in context subclasses.
     // 留给子类的模板方法，允许子类继续对工厂执行一些处理
     postProcessBeanFactory(beanFactory);

     StartupStep beanPostProcess = this.applicationStartup.start("spring.context.beans.post-process");
     // Invoke factory processors registered as beans in the context.
     // 5. 【大核心】工厂增强：执行所有的BeanFactory 后置增强器 利用BeanFactory后置增强器对工厂进行修改或增强
     // 配置类也会在这个解析
     // BeanDefinitionRegistryPostProcessor BeanFactoryPostProcessor 完成对这两个接口的调用
     invokeBeanFactoryPostProcessors(beanFactory);

     // Register bean processors that intercept bean creation.
     // 6. 【核心】注册 所有的Bean的后置处理器
     registerBeanPostProcessors(beanFactory);
     beanPostProcess.end();

     // Initialize message source for this context.
     // 7. 初始化国际化组件
     initMessageSource();

     // Initialize event multicaster for this context.
     // 8. 初始化事件派发 功能
     initApplicationEventMulticaster();

     // Initialize other special beans in specific context subclasses.
     // 9. 留给子类继续增强处理逻辑
     // 这个方法着重理解模板设计模式，因为在springboot中，这个方法是用来做内嵌tomcat启动的
     onRefresh();

     // Check for listener beans and register them.
     // 10. 注册事件监听器，从容器中获取所有的ApplicationListener
     registerListeners();

     // Instantiate all remaining (non-lazy-init) singletons.
     // 11. 【大核心】bean创建：完成BeanFactory 初始化（工厂里面所有的组件都好了）
     /*
      * 这个方法一定要理解要具体看
      * 1、bean实例化过程
      * 2、ioc
      * 3、注解支持
      * 4、BeanPostProcessor的执行
      * 5、Aop的入口
      */
     finishBeanFactoryInitialization(beanFactory);

     // Last step: publish corresponding event.
     // 12. 发布事件
     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();
     contextRefresh.end();
  }

}
}
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我们主要分析几个方法：

3.1 invokeBeanFactoryPostProcessors(beanFactory)
BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessor 方法处理都是在这个步骤中。

直接看 PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors()：

public static void invokeBeanFactoryPostProcessors(

  ConfigurableListableBeanFactory beanFactory, List beanFactoryPostProcessors) {

// WARNING: Although it may appear that the body of this method can be easily
// refactored to avoid the use of multiple loops and multiple lists, the use
// of multiple lists and multiple passes over the names of processors is
// intentional. We must ensure that we honor the contracts for PriorityOrdered
// and Ordered processors. Specifically, we must NOT cause processors to be
// instantiated (via getBean() invocations) or registered in the ApplicationContext
// in the wrong order.
//
// Before submitting a pull request (PR) to change this method, please review the
// list of all declined PRs involving changes to PostProcessorRegistrationDelegate
// to ensure that your proposal does not result in a breaking change:
// https://github.com/spring-pro...

// Invoke BeanDefinitionRegistryPostProcessors first, if any.
Set processedBeans = new HashSet<>();

// 先拿到底层默认有的BeanFactoryPostProcessor，容器会注入ConfigurationClassPostProcessor，配置类的后置处理
if (beanFactory instanceof BeanDefinitionRegistry) {

  BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
  List regularPostProcessors = new ArrayList<>();
  List registryProcessors = new ArrayList<>();

  for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
     if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
        BeanDefinitionRegistryPostProcessor registryProcessor =
              (BeanDefinitionRegistryPostProcessor) postProcessor;
        registryProcessor.postProcessBeanDefinitionRegistry(registry);
        registryProcessors.add(registryProcessor);
     }
     else {
        regularPostProcessors.add(postProcessor);
     }
  }

  // Do not initialize FactoryBeans here: We need to leave all regular beans
  // uninitialized to let the bean factory post-processors apply to them!
  // Separate between BeanDefinitionRegistryPostProcessors that implement
  // PriorityOrdered, Ordered, and the rest.
  List currentRegistryProcessors = new ArrayList<>();

  // First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
  // 首先，从工厂中获取所有的BeanDefinitionRegistryPostProcessor
  String[] postProcessorNames =
        beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
  // 获取所有实现PriorityOrdered 接口的的BeanDefinitionRegistryPostProcessor
  for (String ppName : postProcessorNames) {
     if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
        // 从工厂中获取这个组件（getBean组件的创建）并放到这个集合中
        currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
        processedBeans.add(ppName);
     }
  }
  // 利用优先级排序
  sortPostProcessors(currentRegistryProcessors, beanFactory);
  registryProcessors.addAll(currentRegistryProcessors);
  // todo 执行这些BeanDefinitionRegistryPostProcessor
  invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
  currentRegistryProcessors.clear();

  // Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
  postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
  // 接下来，获取所有实现了Ordered接口的BeanDefinitionRegistryPostProcessor
  for (String ppName : postProcessorNames) {
     // 即使实现了Ordered 和PriorityOrdered接口，以PriorityOrdered接口为准
     if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
        currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
        processedBeans.add(ppName);
     }
  }
  // 排序
  sortPostProcessors(currentRegistryProcessors, beanFactory);
  registryProcessors.addAll(currentRegistryProcessors);
  invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
  currentRegistryProcessors.clear();

  // Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
  // 最后，我们自定义和没有实现 优先级接口的
  boolean reiterate = true;
  while (reiterate) {
     reiterate = false;
     postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
     for (String ppName : postProcessorNames) {
        if (!processedBeans.contains(ppName)) {
           currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
           processedBeans.add(ppName);
           reiterate = true;
        }
     }
     // 排序，根据类名大小写进行排序
     sortPostProcessors(currentRegistryProcessors, beanFactory);
     registryProcessors.addAll(currentRegistryProcessors);
     // todo 执行BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry 方法
     invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry, beanFactory.getApplicationStartup());
     // 防止重复
     currentRegistryProcessors.clear();
  }

  // Now, invoke the postProcessBeanFactory callback of all processors handled so far.
  // todo 接下来，执行BeanDefinitionRegistryPostProcessor.postProcessBeanFactory 的方法
  invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
  invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);

}

else {

  // Invoke factory processors registered with the context instance.
  invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);

}

// todo 上面是执行 BeanDefinitionRegistryPostProcessor，下面是执行 BeanFactoryPostProcessor
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
String[] postProcessorNames =

     beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);

// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List priorityOrderedPostProcessors = new ArrayList<>();
List orderedPostProcessorNames = new ArrayList<>();
List nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {

  if (processedBeans.contains(ppName)) {
     // skip - already processed in first phase above
  }
  else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
     priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
  }
  else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
     orderedPostProcessorNames.add(ppName);
  }
  else {
     nonOrderedPostProcessorNames.add(ppName);
  }

}

// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
// 首先，执行实现PriorityOrdered接口的BeanFactoryPostProcessors
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
// 接下来，执行实现Ordered接口的BeanFactoryPostProcessors
List orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
for (String postProcessorName : orderedPostProcessorNames) {

  orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));

}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

// Finally, invoke all other BeanFactoryPostProcessors.
// 最后，执行没有实现优先级和排序接口的BeanFactoryPostProcessors
List nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
for (String postProcessorName : nonOrderedPostProcessorNames) {

  nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));

}
// todo 执行BeanFactoryPostProcessor.postProcessBeanFactory()方法
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);

// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();
}
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获取到所有BeanDefinitionRegistryPostProcessor并创建对象，首先，执行PriorityOrdered接口，其次，执行Ordered接口，最后，执行没有实现优先级接口，都会执行invokeBeanDefinitionRegistryPostProcessors()方法和invokeBeanFactoryPostProcessors()方法。

3.1.1 invokeBeanDefinitionRegistryPostProcessors()
private static void invokeBeanDefinitionRegistryPostProcessors(

  Collection postProcessors, BeanDefinitionRegistry registry, ApplicationStartup applicationStartup) {

for (BeanDefinitionRegistryPostProcessor postProcessor : postProcessors) {

  StartupStep postProcessBeanDefRegistry = applicationStartup.start("spring.context.beandef-registry.post-process")
        .tag("postProcessor", postProcessor::toString);
  // todo 核心，配置类的后置处理器在此解析配置类
  postProcessor.postProcessBeanDefinitionRegistry(registry);
  postProcessBeanDefRegistry.end();

}
}
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在这里会执行BeanDefinitionRegistryPostProcessor.postProcessBeanDefinitionRegistry方法。

3.1.2 invokeBeanFactoryPostProcessors（）
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);

private static void invokeBeanFactoryPostProcessors(

  Collection postProcessors, ConfigurableListableBeanFactory beanFactory) {

for (BeanFactoryPostProcessor postProcessor : postProcessors) {

  StartupStep postProcessBeanFactory = beanFactory.getApplicationStartup().start("spring.context.bean-factory.post-process")
        .tag("postProcessor", postProcessor::toString);
  // todo
  postProcessor.postProcessBeanFactory(beanFactory);
  postProcessBeanFactory.end();

}
}
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在这里，入参都是BeanDefinitionRegistryPostProcessor 类型的，所以会执行 BeanDefinitionRegistryPostProcessor.postProcessBeanFactory方法。

3.1.3
接下来，获取到所有BeanFactoryPostProcessor并创建对象，首先，执行PriorityOrdered接口，其次，执行Ordered接口，最后，执行没有实现优先级接口，都会执行invokeBeanFactoryPostProcessors()方法。

本次入参是BeanFactoryPostProcessor对象，所以会执行 BeanFactoryPostProcessor.postProcessBeanFactory()方法。

3.1.4 beanFactory.getBeanNamesForType()
spring中如何根据类型获取所有的组件？
DefaultListableBeanFactory#getBeanNamesForType()：

@Override
public String[] getBeanNamesForType(@Nullable Class type, boolean includeNonSingletons, boolean allowEagerInit) {
if (!isConfigurationFrozen() || type == null || !allowEagerInit) {

  // todo
  return doGetBeanNamesForType(ResolvableType.forRawClass(type), includeNonSingletons, allowEagerInit);

}
...
}
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// 获取某一个组件在容器中的名字
private String[] doGetBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit) {
List result = new ArrayList<>();

// Check all bean definitions.
// 因为Spring没有class-bean的对应信息，只能遍历所有的beanName 拿出他们所有的beanName的定义信息，再看是否指定的类型
// 只有在这里bean实例还未创建的时候，才能使用后置处理器干预 bean的类型
for (String beanName : this.beanDefinitionNames) {

  // Only consider bean as eligible if the bean name is not defined as alias for some other bean.
  if (!isAlias(beanName)) {
     try {
        RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
        // Only check bean definition if it is complete.
        if (!mbd.isAbstract() && (allowEagerInit ||
              (mbd.hasBeanClass() || !mbd.isLazyInit() || isAllowEagerClassLoading()) &&
                    !requiresEagerInitForType(mbd.getFactoryBeanName()))) {
           boolean isFactoryBean = isFactoryBean(beanName, mbd);
           BeanDefinitionHolder dbd = mbd.getDecoratedDefinition();
           boolean matchFound = false;
           // containsSingleton(beanName) 是否已经创建单例对象
           boolean allowFactoryBeanInit = (allowEagerInit || containsSingleton(beanName));
           boolean isNonLazyDecorated = (dbd != null && !mbd.isLazyInit());
           if (!isFactoryBean) {
              if (includeNonSingletons || isSingleton(beanName, mbd, dbd)) {
                 // 是否类型匹配
                 matchFound = isTypeMatch(beanName, type, allowFactoryBeanInit);
              }
           }
           else {
              if (includeNonSingletons || isNonLazyDecorated ||
                    (allowFactoryBeanInit && isSingleton(beanName, mbd, dbd))) {
                 // 是否类型匹配
                 matchFound = isTypeMatch(beanName, type, allowFactoryBeanInit);
              }
              if (!matchFound) {
                 // In case of FactoryBean, try to match FactoryBean instance itself next.
                 beanName = FACTORY_BEAN_PREFIX + beanName;
                 if (includeNonSingletons || isSingleton(beanName, mbd, dbd)) {
                    matchFound = isTypeMatch(beanName, type, allowFactoryBeanInit);
                 }
              }
           }
           if (matchFound) {
              result.add(beanName);
           }
        }
     }
     catch (CannotLoadBeanClassException | BeanDefinitionStoreException ex) {
        if (allowEagerInit) {
           throw ex;
        }
        // Probably a placeholder: let's ignore it for type matching purposes.
        LogMessage message = (ex instanceof CannotLoadBeanClassException ?
              LogMessage.format("Ignoring bean class loading failure for bean '%s'", beanName) :
              LogMessage.format("Ignoring unresolvable metadata in bean definition '%s'", beanName));
        logger.trace(message, ex);
        // Register exception, in case the bean was accidentally unresolvable.
        onSuppressedException(ex);
     }
     catch (NoSuchBeanDefinitionException ex) {
        // Bean definition got removed while we were iterating -> ignore.
     }
  }

}

// Check manually registered singletons too.
for (String beanName : this.manualSingletonNames) {

  try {
     // In case of FactoryBean, match object created by FactoryBean.
     if (isFactoryBean(beanName)) {
        if ((includeNonSingletons || isSingleton(beanName)) && isTypeMatch(beanName, type)) {
           result.add(beanName);
           // Match found for this bean: do not match FactoryBean itself anymore.
           continue;
        }
        // In case of FactoryBean, try to match FactoryBean itself next.
        beanName = FACTORY_BEAN_PREFIX + beanName;
     }
     // Match raw bean instance (might be raw FactoryBean).
     if (isTypeMatch(beanName, type)) {
        result.add(beanName);
     }
  }
  catch (NoSuchBeanDefinitionException ex) {
     // Shouldn't happen - probably a result of circular reference resolution...
     logger.trace(LogMessage.format(
           "Failed to check manually registered singleton with name '%s'", beanName), ex);
  }

}

return StringUtils.toStringArray(result);
}
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主要步骤：

拿到所有组件的名字，beanDefinitionNames
遍历每一个组件名字
再去BeanDefinitionMap中找bean的定义信息
从定义信息中获取组件的类型
看这个类型是否匹配
3.2 registerBeanPostProcessors(beanFactory)
注册所有bean的后置处理器， PostProcessorRegistrationDelegate#registerBeanPostProcessors()：

public static void registerBeanPostProcessors(

  ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {

// 获取到容器中所有的BeanPostProcessor， Bean的后置处理器
String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);

// 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));

// Separate between BeanPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List priorityOrderedPostProcessors = new ArrayList<>();
List internalPostProcessors = new ArrayList<>();
List orderedPostProcessorNames = new ArrayList<>();
List nonOrderedPostProcessorNames = new ArrayList<>();
for (String ppName : postProcessorNames) {

  // 获取所有实现了PriorityOrdered接口
  if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
     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.
// 首先，注册实现了PriorityOrdered 接口的 BeanPostProcessor
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);

// Next, register the BeanPostProcessors that implement Ordered.
// 接下来，注册实现了Ordered 接口的 BeanPostProcessor
List orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
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.
// 最后，注册了普通的BeanPostProcessor
List nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
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.
// 最后，注册所有内部的BeanPostProcessors
sortPostProcessors(internalPostProcessors, beanFactory);
registerBeanPostProcessors(beanFactory, internalPostProcessors);

// Re-register post-processor for detecting inner beans as ApplicationListeners,
// moving it to the end of the processor chain (for picking up proxies etc).
// 重新注册一下 ApplicationListenerDetector 这个后置处理器
// 把它放到后置处理器的最后一个位置
beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
}
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这个步骤，将bean的后置处理器BeanPostProcessor、MergedBeanDefinitionPostProcessor、SmartInstantiationAwareBeanPostProcessor、InstantiationAwareBeanPostProcessor都注册并初始话实例。

3.3 registerListeners()
这个核心是注册监听器事件，这个我们后面再说，今天主要说明SmartInstantiationAwareBeanPostProcessor.predictBeanType()干预bean的类型。

/**

Add beans that implement ApplicationListener as listeners.
Doesn't affect other listeners, which can be added without being beans.
多播器和监听器是观察者模式，里面包含了所有的监听器
*/

protected void registerListeners() {
...
// 获取ApplicationListener 在ioc容器中注册的bean的名字
String[] listenerBeanNames = getBeanNamesForType(ApplicationListener.class, true, false);
for (String listenerBeanName : listenerBeanNames) {

  // 获取所有的监听器，并保存他们的名字在
  getApplicationEventMulticaster().addApplicationListenerBean(listenerBeanName);

}
...
}
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也会执行getBeanNamesForType()方法，前面我们简单分析过，我们直接来到：AbstractAutowireCapableBeanFactory#predictBeanType方法：

@Override
@Nullable
protected Class predictBeanType(String beanName, RootBeanDefinition mbd, Class... typesToMatch) {
Class targetType = determineTargetType(beanName, mbd, typesToMatch);
// Apply SmartInstantiationAwareBeanPostProcessors to predict the
// eventual type after a before-instantiation shortcut.
if (targetType != null && !mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {

  boolean matchingOnlyFactoryBean = typesToMatch.length == 1 && typesToMatch[0] == FactoryBean.class;
  // todo 执行SmartInstantiationAwareBeanPostProcessor.predictBeanType方法
  for (SmartInstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().smartInstantiationAware) {
     Class predicted = bp.predictBeanType(targetType, beanName);
     if (predicted != null &&
           (!matchingOnlyFactoryBean || FactoryBean.class.isAssignableFrom(predicted))) {
        return predicted;
     }
  }

}
return targetType;
}
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在3.1节中执行Bean工厂的后置处理器的时候，hasInstantiationAwareBeanPostProcessors()为false,所以进入不了这个方法，原因是因为在invokeBeanFactoryPostProcessors()方法的时候，BeanPostProcessor在容器中还没有，所以不会执行。

但是，registerListeners()在registerBeanPostProcessors()方法之后，所以可以执行这个方法，也就是SmartInstantiationAwareBeanPostProcessor.predictBeanType()干预bean的组件类型。

3.4 finishBeanFactoryInitialization()
完成BeanFactory 初始化（工厂里面所有的组件都好了）。 beanFactory.preInstantiateSingletons()-> getBean(beanName)->doGetBean->createBean

protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)

  throws BeanCreationException {

...
try {

  // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
  // todo 提前给我们一个机会，去返回组件的代理对象
  Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
  if (bean != null) {
     return bean;
  }

}
...
try {

  // todo 创建对象
  Object beanInstance = doCreateBean(beanName, mbdToUse, args);
  if (logger.isTraceEnabled()) {
     logger.trace("Finished creating instance of bean '" + beanName + "'");
  }
  return beanInstance;

}
...
}
复制代码
3.4.1 resolveBeforeInstantiation(beanName, mbdToUse)
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
Object bean = null;
if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {

  // Make sure bean class is actually resolved at this point.
  if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
     Class targetType = determineTargetType(beanName, mbd);
     if (targetType != null) {
        // todo InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation()方法
        bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
        if (bean != null) {
           bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
        }
     }
  }
  mbd.beforeInstantiationResolved = (bean != null);

}
return bean;
}
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protected Object applyBeanPostProcessorsBeforeInstantiation(Class beanClass, String beanName) {
for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {

  // todo  执行
  Object result = bp.postProcessBeforeInstantiation(beanClass, beanName);
  if (result != null) {
     return result;
  }

}
return null;
}
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在这里执行 InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation()方法。如果该方法返回true,则直接执行applyBeanPostProcessorsAfterInitialization()方法：

public Object applyBeanPostProcessorsAfterInitialization(Object existingBean, String beanName)

  throws BeansException {

Object result = existingBean;
// todo 执行所有BeanPostProcessor.postProcessAfterInitialization()方法
// 所有的BeanPostProcessor类型
for (BeanPostProcessor processor : getBeanPostProcessors()) {

  Object current = processor.postProcessAfterInitialization(result, beanName);
  if (current == null) {
     return result;
  }
  result = current;

}
return result;
}
复制代码
在这里执行所有BeanPostProcessor.postProcessAfterInitialization()方法。

接下来，我们看一下doCreateBean方法。

3.4.2 doCreaeBean
protected Object doCreateBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)

  throws BeanCreationException {

// Instantiate the bean.
BeanWrapper instanceWrapper = null;
// 是否单例
if (mbd.isSingleton()) {

  instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);

}
if (instanceWrapper == null) {

  // todo 创建Bean实例 ，默认使用无参构造器创建的对象，组件的实例就创建了
  instanceWrapper = createBeanInstance(beanName, mbd, args);

}
Object bean = instanceWrapper.getWrappedInstance();
Class beanType = instanceWrapper.getWrappedClass();
if (beanType != NullBean.class) {

  mbd.resolvedTargetType = beanType;

}

// Allow post-processors to modify the merged bean definition.
// MergedBeanDefinitionPostProcessor 后置处理器再来修改下BeanDefinition 信息
synchronized (mbd.postProcessingLock) {

  if (!mbd.postProcessed) {
     try {
        // todo 执行MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition()方法
        applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
     }
     catch (Throwable ex) {
        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
              "Post-processing of merged bean definition failed", ex);
     }
     mbd.postProcessed = true;
  }

}

// Eagerly cache singletons to be able to resolve circular references
// even when triggered by lifecycle interfaces like BeanFactoryAware.
// 提前暴露单实例bean 专门来解决循坏引用的问题
boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&

     isSingletonCurrentlyInCreation(beanName));

if (earlySingletonExposure) {

  if (logger.isTraceEnabled()) {
     logger.trace("Eagerly caching bean '" + beanName +
           "' to allow for resolving potential circular references");
  }
  // 添加
  // 三级缓存中Bean也会被后置处理来增强
  addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));

}

// Initialize the bean instance.
Object exposedObject = bean;
try {

  // todo 对象中的每个属性赋值
  populateBean(beanName, mbd, instanceWrapper);
  // todo 初始化Bean
  exposedObject = initializeBean(beanName, exposedObject, mbd);

}
...

return exposedObject;
}
复制代码
3.4.2.1 createBeanInstance(beanName, mbd, args)
创建bean实例，默认使用无参构造器。

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
// Make sure bean class is actually resolved at this point.
// 创建bean的类型
Class beanClass = resolveBeanClass(mbd, beanName);
...

// Candidate constructors for autowiring?
// todo 候选的构造器 SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors()
// 后置处理器有机会在这个决定当前bean使用哪个构造器
Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||

     mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
  // 构造器的方式自动注入与对象创建
  return autowireConstructor(beanName, mbd, ctors, args);

}

// Preferred constructors for default construction?
// 使用默认的自己设置的高优先级的构造器
ctors = mbd.getPreferredConstructors();
if (ctors != null) {

  return autowireConstructor(beanName, mbd, ctors, null);

}

// No special handling: simply use no-arg constructor.
// 默认使用无参构造器为当前组件创建对象
return instantiateBean(beanName, mbd);
}
复制代码
在determineConstructorsFromBeanPostProcessors方法中可以决定使用构造器。

protected Constructor[] determineConstructorsFromBeanPostProcessors(@Nullable Class beanClass, String beanName)

  throws BeansException {

if (beanClass != null && hasInstantiationAwareBeanPostProcessors()) {

  for (SmartInstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().smartInstantiationAware) {
     // todo 执行SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors()方法
     Constructor[] ctors = bp.determineCandidateConstructors(beanClass, beanName);
     if (ctors != null) {
        return ctors;
     }
  }

}
return null;
}
复制代码
在这里执行SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors()方法。

3.4.2.2 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName)
protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class beanType, String beanName) {
// todo 执行MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition()方法
for (MergedBeanDefinitionPostProcessor processor : getBeanPostProcessorCache().mergedDefinition) {

  processor.postProcessMergedBeanDefinition(mbd, beanType, beanName);

}
}
复制代码
在这里执行MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition()方法。

3.4.2.3 populateBean(beanName, mbd, instanceWrapper)
对每个属性进行赋值操作。

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
...

// 属性赋值之前，后置处理器可以提前准备些东西
// @AutoWired 赋值也在这里 AutowiredAnnotationBeanPostProcessor(直接返回true 没有其他的处理)，可以中断初始化行为
//
if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {

  for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
     // todo 执行InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation() 方法
     if (!bp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
        return;
     }
  }

} // 以上的后置处理器可以中断下面的初始化行为

...

boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
boolean needsDepCheck = (mbd.getDependencyCheck() != AbstractBeanDefinition.DEPENDENCY_CHECK_NONE);

PropertyDescriptor[] filteredPds = null;
if (hasInstAwareBpps) {

  if (pvs == null) {
     // xml中property标签指定的
     pvs = mbd.getPropertyValues();
  }
  // 注解版的属性赋值 后置处理器处理属性（真正的自动装配）
  for (InstantiationAwareBeanPostProcessor bp : getBeanPostProcessorCache().instantiationAware) {
     // todo 执行InstantiationAwareBeanPostProcessor.postProcessProperties() 方法
     PropertyValues pvsToUse = bp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
     if (pvsToUse == null) {
        if (filteredPds == null) {
           filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
        }
        pvsToUse = bp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
        if (pvsToUse == null) {
           return;
        }
     }
     pvs = pvsToUse; //  封装了当前bean的所有属性名和值，可以由后置处理器处理得到
  }

}
...

if (pvs != null) { // 把以前处理好的PropertyValues 给bean里面设置一下，主要是上面步骤没有给bean里面设置的属性

  // xml版 的所有配置会来到这里 给属性赋值
  applyPropertyValues(beanName, mbd, bw, pvs);

}
}
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这里，会执行2个后置处理器的方法：

执行InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation() 方法
执行InstantiationAwareBeanPostProcessor.postProcessProperties() 方法
3.4.2.4 initializeBean(beanName, exposedObject, mbd)
对bean进行初始化操作。

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
if (System.getSecurityManager() != null) {

  AccessController.doPrivileged((PrivilegedAction

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