循环依赖判断

// 判断处理依赖引用
if (earlySingletonExposure) {
    // 从缓存中获取bean
    Object earlySingletonReference = getSingleton(beanName, false);
    if (earlySingletonReference != null) {
        if (exposedObject == bean) {
            exposedObject = earlySingletonReference;
            // 判断是否有其他依赖的bean
        } 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);
                }
            }
            // 如果依然有bean在创建中，异常
            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 " +
                    "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
            }
        }
    }
}

1. 从缓存中尝试获取该bean；
2. 判断 exposedObject == bean ，最开始它们是相等的 Object exposedObject = bean；经过初始化后，exposedObject 有可能变成了代理对象。如果相等的话，那么说明没有被代理；不等的话，exposedObject 已经变成了 bean 的代理对象。
3. 检测这个代理对象所有依赖的 bean 是否都初始化好了，如果没有的话 BeanCurrentlyInCreationException 。