Spring IOC源码：registerBeanPostProcessors 详解

2023-06-12 89

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简介： Spring IOC源码：registerBeanPostProcessors 详解

文章目录

自定义

总结

Spring源码系列：

Spring IOC源码：简单易懂的Spring IOC 思路介绍

Spring IOC源码：核心流程介绍

Spring IOC源码：ApplicationContext刷新前准备工作

Spring IOC源码：obtainFreshBeanFactory 详解（上）

Spring IOC源码：obtainFreshBeanFactory 详解（中）

Spring IOC源码：obtainFreshBeanFactory 详解（下）

Spring IOC源码：＜context:component-scan＞源码详解

Spring IOC源码：invokeBeanFactoryPostProcessors 后置处理器详解

Spring IOC源码：registerBeanPostProcessors 详解

Spring IOC源码：实例化前的准备工作

Spring IOC源码：finishBeanFactoryInitialization详解

Spring IoC源码：getBean 详解

Spring IoC源码：createBean（上）

Spring IoC源码：createBean（中）

Spring IoC源码：createBean（下）

Spring IoC源码：finishRefresh 完成刷新详解

前言

上篇文章介绍了后置处理器BeanFactoryPostProcessor的注册、实例化及执行操作，这节介绍一下另外一个后置处理器BeanPostProcessor。前者是针对BeanFactory工厂对象进行增上改查操作，在bean实例化之前，我们可以修改其定义。后者是对实例化后的初始化环节前后对实例对象进行操作。

正文

进入refresh中的registerBeanPostProcessors(beanFactory)方法。该方法会将beanFactory工厂中所有BeanPostProcessor类型的BeanDefinition定义信息进行实例化注册，以便在bean的初始化环节中调用。

  protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory) {
    PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this);
  }

PostProcessorRegistrationDelegate.registerBeanPostProcessors(beanFactory, this)，见方法1详解

方法1：registerBeanPostProcessors

public static void registerBeanPostProcessors(
      ConfigurableListableBeanFactory beanFactory, AbstractApplicationContext applicationContext) {
    //从BeanFactory工厂中获取BeanPostProcessor的实现类beanName
    String[] postProcessorNames = beanFactory.getBeanNamesForType(BeanPostProcessor.class, true, false);
    //定义目标长度
    int beanProcessorTargetCount = beanFactory.getBeanPostProcessorCount() + 1 + postProcessorNames.length;
    //添加BeanPostProcessorChecker到beanFactory工厂中的beanPostProcessors集合中
    //这是个内部类,用来检查是否在bean的创建过程中,经过了所有本来应经过的后置处理器
    beanFactory.addBeanPostProcessor(new BeanPostProcessorChecker(beanFactory, beanProcessorTargetCount));
    //实现了PriorityOrdered接口的后置处理器集合
    List<BeanPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    //内部的后置处理器集合
    List<BeanPostProcessor> internalPostProcessors = new ArrayList<>();
    //实现了Ordered接口的后置处理器集合
    List<String> orderedPostProcessorNames = new ArrayList<>();
    //普通后置处理器集合
    List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    for (String ppName : postProcessorNames) {
      if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
        //实例化，获取对象
        BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
        priorityOrderedPostProcessors.add(pp);
        //  内部类型
        if (pp instanceof MergedBeanDefinitionPostProcessor) {
          internalPostProcessors.add(pp);
        }
      }
      //Ordered类型
      else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
        orderedPostProcessorNames.add(ppName);
      }
      else {
        nonOrderedPostProcessorNames.add(ppName);
      }
    }
    //对集合中的后置处理器进行排序
    sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    //加入到工厂集合中
    registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors);
    // Next, register the BeanPostProcessors that implement Ordered.
    List<BeanPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    //将上述归类好的后置处理器进行实例化，并筛选出内部后置处理器
    for (String ppName : orderedPostProcessorNames) {
      BeanPostProcessor pp = beanFactory.getBean(ppName, BeanPostProcessor.class);
      orderedPostProcessors.add(pp);
      if (pp instanceof MergedBeanDefinitionPostProcessor) {
        internalPostProcessors.add(pp);
      }
    }
    //排序
    sortPostProcessors(orderedPostProcessors, beanFactory);
    //注册添加到集合中
    registerBeanPostProcessors(beanFactory, orderedPostProcessors);
    // 处理普通的后置处理器
    List<BeanPostProcessor> 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);
      }
    }
    //注册添加到集合中
    registerBeanPostProcessors(beanFactory, nonOrderedPostProcessors);
    // 最后对所有的内部后置处理器进行排序，注册处理
    sortPostProcessors(internalPostProcessors, beanFactory);
    registerBeanPostProcessors(beanFactory, internalPostProcessors);
    //移除之前添加的ApplicationListenerDetector，将其放到最后端
    beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext));
  }

sortPostProcessors(priorityOrderedPostProcessors, beanFactory)，方法我们在上篇文章中讲解《invokeBeanFactoryPostProcessors》中方法6

registerBeanPostProcessors(beanFactory, priorityOrderedPostProcessors)，见方法2详解

beanFactory.addBeanPostProcessor(new ApplicationListenerDetector(applicationContext))：

之前在refresh中的方法prepareBeanFactory添加过ApplicationListenerDetector，这里主要是排序，将该类型的后置处理器移到最后面来。

方法2：registerBeanPostProcessors

  private static void registerBeanPostProcessors(
      ConfigurableListableBeanFactory beanFactory, List<BeanPostProcessor> postProcessors) {
    for (BeanPostProcessor postProcessor : postProcessors) {
      beanFactory.addBeanPostProcessor(postProcessor);
    }
  }

  public void addBeanPostProcessor(BeanPostProcessor beanPostProcessor) {
    Assert.notNull(beanPostProcessor, "BeanPostProcessor must not be null");
    // 如果之前容器中存在该对象，则移除
    this.beanPostProcessors.remove(beanPostProcessor);
    // 如果是InstantiationAwareBeanPostProcessor类型的后置处理器，则标识为已注册
    if (beanPostProcessor instanceof InstantiationAwareBeanPostProcessor) {
      this.hasInstantiationAwareBeanPostProcessors = true;
    }
    // 如果是DestructionAwareBeanPostProcessor类型的后置处理器，则标识为已注册
    if (beanPostProcessor instanceof DestructionAwareBeanPostProcessor) {
      this.hasDestructionAwareBeanPostProcessors = true;
    }
    // 添加到集合末尾
    this.beanPostProcessors.add(beanPostProcessor);
  }

自定义

我们知道BeanPostProcessor实现类会在bean实例化后，初始化环节中进行调用，那我们如何自定义一个BeanPostProcessor 实现类并注册到工厂中呢？上篇文章我们演示了如何自定义BeanFactoryPostProcessor，其操作方法也是类型的；

1、自定义BeanPostProcessor

public class MyBeanPostProcessor implements BeanPostProcessor {
  @Override
  public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("after:"+beanName);
    return null;
  }
  @Override
  public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    System.out.println("before:"+beanName);
    return null;
  }
}

2、自定义上下文子类

通过拓展接口postProcessBeanFactory我们可以拿到工厂对象，并对其注册。

public class MyClassPathApplicationContext extends ClassPathXmlApplicationContext {
  public MyClassPathApplicationContext(String path){
    super(path);
  }
  @Override
  protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
    beanFactory.addBeanPostProcessor(new MyBeanPostProcessor());
  }
}

3、编写入口

public class PersonTest {
  public static void main(String[] args) {
    MyClassPathApplicationContext applicationContext=new MyClassPathApplicationContext("application-scan.xml");
    StudentDao zdcDomain = (StudentDao) applicationContext.getBean("studentDao");
    System.out.println(zdcDomain);
  }
}