public @interface Scope

How many instances of a bean there are, and how long each lives.

• singleton (the default) – one, for the life of the server.
• prototype – a new one for every injection point.
• request – one per HTTP request, built when the request first uses it.
• session – one per HttpSession.

A request or session bean injected into a singleton is reached through a small class the build generates, which finds the current request’s instance on each call. That class extends the bean’s, so a request or session bean cannot be final, needs a constructor taking no arguments, and has that constructor run once at start-up for the stand-in – per-request set-up belongs in @PostConstruct, which runs on each real instance.