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Spring几个PostProcessor的区别 浅谈Spring中几个PostProcessor的区别与联系

硕子鸽 人气:0
想了解浅谈Spring中几个PostProcessor的区别与联系的相关内容吗,硕子鸽在本文为您仔细讲解Spring几个PostProcessor的区别的相关知识和一些Code实例,欢迎阅读和指正,我们先划重点:Spring,PostProcessor,PostProcessor区别,下面大家一起来学习吧。

Spring几个PostProcessor的区别

首先明确 Bean 的生命周期:

按照执行的顺序,可以分为以下几个步骤:

BeanDefinitionRegistryPostProcessor 是在注册 Bean 定义信息前后调用;

BeanFactoryPostProcessor 是在创建 Bean 前后调用;

BeanPostProcessor 是在初始化 Bean 前后调用;

其中 BeanDefinitionRegistryPostProcessor 是 BeanFactoryPostProcessor 的子类,所以可以使用前者代替后者实现功能。

查看 IOC 容器创建时的调用流程

refresh 方法的代码如下:

// 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.
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();

其中的 invokeBeanFactoryPostProcessors 就执行了注册定义信息和创建 Bean 的方法;而 finishBeanFactoryInitialization 执行了初始化 Bean 的方法。

具体的执行顺序大家可以自行打断点调试,由于涉及的源码过多,这里不再展示。

spring-postProcessor的执行时机

spring bean 的生命周期粗糙的分为以下步骤。

实例化(创建一个属性都为空的对象)---------》属性填充(populateBean,下文中这个步骤我都称为初始化)-----------》init方法的执行(invokerInitMethods,下文称为init)

postprocessor的方法就是穿插在这三个大的步骤中。

BeanPostProcessor:

postProcessBeforeInitialization调用时机

向上找调用者:

继续向上:

看以看出populateBean(初始化bean)-------------------》beanpostBeforeInitialization---------------------------------->invokeinitMethods(配置的init-method)

postProcessAfterInitialization调用时机:

向上:

可以看出在init-method方法之后

看以看出populateBean(初始化bean)-------------------》beanpostBeforeInitialization---------------------------------->invokeinitMethods(配置的init-method)------->postProcessAfterInitialization

public class MBeanPostProcessor implements BeanPostProcessor { 
    @Override
    //populateBean之后   invokeinitMethods之前
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("post bean before! :"+beanName);
        return bean;
    }
 
    @Override
    //invokeinitMethods之后
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("post bean after!"+beanName);
        return bean;
    }
}

另一个重要的是:

InstantiationAwareBeanPostProcessor

postProcessBeforeInstantiation调用时机:

向上找调用者:

继续向上:

可以看出是在实例化之前:(也就是反射创建对象之前,如果postProcessBeforeInstantiation创建了一个非空的对象,则不会走实例化步骤。

postProcessAfterInstantiation调用时机:

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
   PropertyValues pvs = mbd.getPropertyValues();
 
   if (bw == null) {
      if (!pvs.isEmpty()) {
         throw new BeanCreationException(
               mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
      }
      else {
         // Skip property population phase for null instance.
         return;
      }
   }
 
   // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
   // state of the bean before properties are set. This can be used, for example,
   // to support styles of field injection.
   boolean continueWithPropertyPopulation = true;
 
   if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
         if (bp instanceof InstantiationAwareBeanPostProcessor) {
            InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
            //在这里执行
            if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
               continueWithPropertyPopulation = false;
               break;
            }
         }
      }
   }
 
   if (!continueWithPropertyPopulation) {
      return;
   }
 省略。。。。。 
   applyPropertyValues(beanName, mbd, bw, pvs);
}

可以看出是在在初始化之前,具体是属性填充之前。(初始化之前,实例化之后) 如果返回fales,则不会继续初始化,即不会属性填充。

postProcessPropertyValues调用时机:

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw) {
   PropertyValues pvs = mbd.getPropertyValues(); 
   if (bw == null) {
      if (!pvs.isEmpty()) {
         throw new BeanCreationException(
               mbd.getResourceDescription(), beanName, "Cannot apply property values to null instance");
      }
      else {
         // Skip property population phase for null instance.
         return;
      }
   }
 
   // Give any InstantiationAwareBeanPostProcessors the opportunity to modify the
   // state of the bean before properties are set. This can be used, for example,
   // to support styles of field injection.
   boolean continueWithPropertyPopulation = true;
 
   if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
         if (bp instanceof InstantiationAwareBeanPostProcessor) {
            InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
            if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) {
               continueWithPropertyPopulation = false;
               break;
            }
         }
      }
   }
 
   if (!continueWithPropertyPopulation) {
      return;
   }
 
   if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME ||
         mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
      MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
 
      // Add property values based on autowire by name if applicable.
      if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) {
         autowireByName(beanName, mbd, bw, newPvs);
      }
 
      // Add property values based on autowire by type if applicable.
      if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) {
         autowireByType(beanName, mbd, bw, newPvs);
      } 
      pvs = newPvs;
   }
 
   boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();
   boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);
 
   if (hasInstAwareBpps || needsDepCheck) {
      PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
      if (hasInstAwareBpps) {
         for (BeanPostProcessor bp : getBeanPostProcessors()) {
            if (bp instanceof InstantiationAwareBeanPostProcessor) {
               InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
               pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
               if (pvs == null) {
                  return;
               }
            }
         }
      }
      if (needsDepCheck) {
         checkDependencies(beanName, mbd, filteredPds, pvs);
      }
   } 
   applyPropertyValues(beanName, mbd, bw, pvs);
}

在postProcessAfterInstantiation之后,applyPropertyValues之前。(属性填充之前修改属性值)

总结: 执行顺序

如果加上aware

以上为个人经验,希望能给大家一个参考,也希望大家多多支持。

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