Invoked right at the end of the singleton pre-instantiation phase, with a guarantee that all regular singleton beans have been created already. {@link ListableBeanFactory#getBeansOfType} calls withinthis method won't trigger accidental side effects during bootstrap.
NOTE: This callback won't be triggered for singleton beans lazily initialized on demand after {@link BeanFactory} bootstrap,and not for any other bean scope either. Carefully use it for beans with the intended bootstrap semantics only.