什么情况下出现循环依赖？

并非使用者手动去getBean才会加载并初始化，而是框架启动时进行加载Spring创建

Bean - #DefaultListableBeanFactory#preInstantiateSingletons
@Overridepublic void preInstantiateSingletons() throws BeansException {        //......        List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);
    // Trigger initialization of all non-lazy singleton beans...    for (String beanName : beanNames) {        RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);        if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {            if (isFactoryBean(beanName)) {                //FactoryBean接口处理                ......            }            else {                //正常Bean的加载入口                getBean(beanName);            }        }    }        //......}