spring-doCreateBean

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
           throws BeanCreationException {
 
       // Instantiate the bean.
       BeanWrapper instanceWrapper = null;
       if (mbd.isSingleton()) {
           instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
       }
 
       // 创建bean实例
       // 1、 如果定义了工厂方法,则用工厂方法方法创建实例
       //    注意，此处的工厂bean指的是配置了factory-bean/factory-method属性的bean，不是实现了FacrotyBean接口的bean。
       //    如果没有配置factory-bean属性，那么factory-method指向的方法必须是静态的。
       // 2、通过构造器创建bean实例
       //    获取正确的构造器, 调用SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors方法,
       //    实际是 AutowiredAnnotationBeanPostProcessor.determineCandidateConstructors方法:
       //      1)如果构造器上面有@Autowire或@Value注解
       //      2)如果只有一个构造函数，且不是默认的构造函数
       // 3、使用无参的默认构造函数：  BeanUtils.instantiateClass(constructorToUse);
       if (instanceWrapper == null) {
           instanceWrapper = createBeanInstance(beanName, mbd, args);
       }
       final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);
       Class beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
       mbd.resolvedTargetType = beanType;
 
       // Allow post-processors to modify the merged bean definition.
       synchronized (mbd.postProcessingLock) {
           if (!mbd.postProcessed) {
               try {
                   // 调用 MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition
                   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.
       boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
               isSingletonCurrentlyInCreation(beanName));
       if (earlySingletonExposure) {
           if (logger.isDebugEnabled()) {
               logger.debug("Eagerly caching bean '" + beanName +
                       "' to allow for resolving potential circular references");
           }
           addSingletonFactory(beanName, new ObjectFactory