聊透Spring bean的生命周期

// 源码位于 AbstractAutowireCapableBeanFactory.java
protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
   // 再次解析BeanDefinition的class,确保class已经被解析
   Class<?> beanClass = resolveBeanClass(mbd, beanName);

   // 1: 如果提供了Supplier,通过Supplier产生对象
   Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
   if (instanceSupplier != null) {
      return obtainFromSupplier(instanceSupplier, beanName);
   }

   // 2: 如果有工厂方法,使用工厂方法产生对象
   // 在@Configration配置@Bean的方法,也会被解析为FactoryMethod
   if (mbd.getFactoryMethodName() != null) {
      return instantiateUsingFactoryMethod(beanName, mbd, args);
   }
   //...省略部分代码
   // 3: 推断构造方法
   // 3.1 执行后置处理器,获取候选构造方法
   Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
   // 3.2 需要自动注入的情况
   if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
         mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
      return autowireConstructor(beanName, mbd, ctors, args);
   }

   // 3.3 默认使用没有参数的构造方法
   return instantiateBean(beanName, mbd);
}

protected void applyMergedBeanDefinitionPostProcessors(RootBeanDefinition mbd, Class<?> beanType, String beanName){
   for (BeanPostProcessor bp : getBeanPostProcessors()) {
      if (bp instanceof MergedBeanDefinitionPostProcessor) {
         MergedBeanDefinitionPostProcessor bdp = (MergedBeanDefinitionPostProcessor) bp;
         bdp.postProcessMergedBeanDefinition(mbd, beanType, beanName);
      }
   }
}

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");
   }
   // 做循环依赖的支持 将早期实例化bean的ObjectFactory,添加到单例工厂(三级缓存)中
   addSingletonFactory(beanName, () getEarlyBeanReference(beanName, mbd, bean));
}

protected void populateBean(String beanName, RootBeanDefinition mbd, @Nullable BeanWrapper bw){
   // 省略部分代码
    
   // 获取bean的注入类型
   int resolvedAutowireMode = mbd.getResolvedAutowireMode();
   // 1: 自动注入
   if (resolvedAutowireMode == AUTOWIRE_BY_NAME || resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
      MutablePropertyValues newPvs = new MutablePropertyValues(pvs);
      // Add property values based on autowire by name if applicable.
      if (resolvedAutowireMode == AUTOWIRE_BY_NAME) {
         // 根据名称注入
         autowireByName(beanName, mbd, bw, newPvs);
      }
      // Add property values based on autowire by type if applicable.
      if (resolvedAutowireMode == AUTOWIRE_BY_TYPE) {
         // 根据类型注入
         autowireByType(beanName, mbd, bw, newPvs);
      }
      pvs = newPvs;
   }


   // 2: 调用BeanPostProcessor，完成@Autowired @Resource属性填充
   PropertyDescriptor[] filteredPds = null;
   if (hasInstAwareBpps) {
      if (pvs == null) {
         pvs = mbd.getPropertyValues();
      }
      for (BeanPostProcessor bp : getBeanPostProcessors()) {
         if (bp instanceof InstantiationAwareBeanPostProcessor) {
            InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;

            // 重点: 完成@Autowired @Resource属性填充
            PropertyValues pvsToUse = ibp.postProcessProperties(pvs, bw.getWrappedInstance(), beanName);
            if (pvsToUse == null) {
               if (filteredPds == null) {
                  // 需要注入的属性,会过滤掉Aware接口包含的属性(通过ignoreDependencyInterface添加)
                  filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
               }
               pvsToUse = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
               if (pvsToUse == null) {
                  return;
               }
            }
            pvs = pvsToUse;
         }
      }
   }
  
    // 3: 依赖检查
   if (needsDepCheck) {
      if (filteredPds == null) {
         filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching);
      }
      checkDependencies(beanName, mbd, filteredPds, pvs);
   }
   // 4: 将属性应用到bean中
   if (pvs != null) {
      applyPropertyValues(beanName, mbd, bw, pvs);
   }
}

protected Object initializeBean(String beanName, Object bean, @Nullable RootBeanDefinition mbd) {
  // 1: 回调Aware接口中的方法
  // 完成Aware方法的回调(BeanNameAware,BeanClassLoaderAware,BeanFactoryAware)
  invokeAwareMethods(beanName, bean);

   Object wrappedBean = bean;
   if (mbd == null || !mbd.isSynthetic()) {
      // 2: 调用before...方法
      // ApplicationContextAwareProcessor: 其他Aware方法的回调
      // InitDestroyAnnotationBeanPostProcessor: @PostConstruct方法的回调
      wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);
   }

   try {
      // 3: 完成xml版本和@bean(initMethod)的init方法回调
      invokeInitMethods(beanName, wrappedBean, mbd);
   }

   // 4: 调用after方法
   // 重点: AOP生成代理对象
   if (mbd == null || !mbd.isSynthetic()) {
      wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
   }

   return wrappedBean;
}