Bean

Singleton, prototype, request/session and other Spring bean scopes, including lifecycle and thread-safety implications.

From bean definition and instantiation through dependency injection, post-processors, initialization, proxies, use, and destruction.

BeanFactory as Spring's dependency-container contract and its relationship with ApplicationContext.

Constructor versus setter/field cycles, early references, proxy complications, and why redesign is usually preferable.

How to express real bean dependencies instead of relying on incidental initialization order.