【追根究底】doCreateBean中为什么会对earlySingletonExposure处理两次

 

转载：https://www.freesion.com/article/9459909831/

 

• 问题对应的代码片段

  protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
  		throws BeanCreationException {
  
  	……
  	// 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));
  	//第一次处理		
  	if (earlySingletonExposure) {
  		if (logger.isTraceEnabled()) {
  			logger.trace("Eagerly caching bean '" + beanName +
  					"' to allow for resolving potential circular references");
  		}
  		addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
  	}
  
  	// Initialize the bean instance.
  	Object exposedObject = bean;
  	try {
  		populateBean(beanName, mbd, instanceWrapper);
  		exposedObject = initializeBean(beanName, exposedObject, mbd);
  	}
  	catch (Throwable ex) {
  		if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
  			throw (BeanCreationException) ex;
  		}
  		else {
  			throw new BeanCreationException(
  					mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
  		}
  	}
      
      //第二次处理
  	if (earlySingletonExposure) {
  		Object earlySingletonReference = getSingleton(beanName, false);
  		if (earlySingletonReference != null) {
  			if (exposedObject == bean) {
  				exposedObject = earlySingletonReference;
  			}
  			else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
  				String[] dependentBeans = getDependentBeans(beanName);
  				Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
  				for (String dependentBean : dependentBeans) {
  					if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
  						actualDependentBeans.add(dependentBean);
  					}
  				}
  				if (!actualDependentBeans.isEmpty()) {
  					throw new BeanCurrentlyInCreationException(beanName,
  							"Bean with name '" + beanName + "' has been injected into other beans [" +
  							StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
  							"] in its raw version as part of a circular reference, but has eventually been " +
  							"wrapped. This means that said other beans do not use the final version of the " +
  							"bean. This is often the result of over-eager type matching - consider using "