Ámbitos de los beans y gestión del ciclo de vida

A scope defines how many instances of a bean Spring creates and how long they live. The default scope is singleton: one shared instance per container.

With singleton, every injection point receives the same object. This is ideal for stateless services and is the most common choice.

The prototype scope creates a new instance every time the bean is requested. Use it for stateful or short-lived objects.

In web apps you also have request and session scopes, tying a bean's lifetime to a single HTTP request or a user session respectively.

• request — one per HTTP request
• session — one per user session

Default to singleton for stateless logic. Reach for other scopes only when a bean must hold per-request or per-instance state, since wider sharing of mutable state causes bugs.

Spring instantiates a bean, injects its dependencies, runs initialization callbacks, serves it during the app's life, and finally runs destruction callbacks on shutdown.

Annotate a method with @PostConstruct to run setup logic after dependencies are injected, such as opening a connection or warming a cache.

A @PreDestroy method runs just before the bean is removed, letting you release resources cleanly.

By default singletons are created at startup. Marking a bean @Lazy defers creation until it is first needed, which can speed up boot time for rarely used beans.

Be aware that Spring does not manage the full destruction lifecycle of prototype beans. The container hands them off and forgets them, so you must release their resources yourself.

A typical singleton service uses @PostConstruct to initialize and @PreDestroy to clean up, giving you precise control over startup and shutdown behavior.

You learned the singleton, prototype, request, and session scopes, the bean lifecycle, and how to hook into it with @PostConstruct, @PreDestroy, and @Lazy.