Spring Prevent setting parent bean factory to self

If set parent bean factory to self, once try to get an undefined bean, bellow condition if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { ... } will always be true and StackOverflowError will be thrown. Sometimes, this issue is hard to detect during runtime, if self-reference is not allowed here, error will be found at the early time of startup. Also, a self-reference parent bean factory is valueless.

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