Recap: Bean Scopes and Lifecycle Callbacks

Singleton and prototype, shared state, clean-up, and scoped proxies, with where each was.

Scopes and lifecycle callbacks come down to the five ideas below, each listed with the card that covers it.

What the topic established, and which card it was on
The idea	Where
Singleton is one shared instance; prototype is a new one per request for the bean	Bean Scopes: Singleton and Prototype
Two `getBean` calls on a prototype return two different objects	Bean Scopes Example: A Prototype Gives a New Instance Each Time
A changing field in a singleton is shared by every caller, and races under load	Mutable State in a Singleton Bean
The container never calls `@PreDestroy` on a prototype; the caller cleans it up	@PostConstruct and @PreDestroy: Lifecycle Callbacks and Prototype Beans
A request-scoped bean needs a scoped proxy before a singleton can use it	Request-Scoped Beans in a Singleton: Why a Scoped Proxy Is Needed

The question behind all five is when a bean is created and who holds it afterwards: answer that, and the right scope and the right clean-up follow.

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