What bean scopes does Spring provide, and when do they matter?

Explains singleton, prototype, request, session, application, and WebSocket scopes as container lifecycle policies.

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TL;DR

Spring's default singleton scope creates one shared instance per bean definition per ApplicationContext. Prototype creates a new instance each time that bean is requested or injected. In a web-aware context, request, session, application, and WebSocket scopes tie an instance to those lifecycles. A Spring singleton is not a JVM-wide guarantee and is not the same as hard-coding the GoF singleton pattern. Scope controls instance reuse; it does not make an object thread-safe.

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Per-container identity, web-scope boundaries, state ownership, proxies, and the difference from the GoF singleton pattern.

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Core answer
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Overview
A scope tells the container when to create and reuse an instance for one bean definition.
Spring's default singleton scope creates one shared instance per bean definition per ApplicationContext. Prototype creates a new instance each time that bean is requested or injected. In a web-aware context, request, session, application, and WebSocket scopes tie an instance to those lifecycles. A Spring singleton is not a JVM-wide guarantee and is not the same as hard-coding the GoF singleton pattern. Scope controls instance reuse; it does not make an object thread-safe.
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Stateless services are usually singleton because they can be shared safely when collaborators and state are designed correctly. Request-scoped state can represent one request, but injecting it into a singleton requires a scoped proxy or provider so resolution occurs in the active request. Prototype is useful for stateful or parameterized instances only when the caller understands ownership, because injection into a singleton happens once unless lookup is deferred.

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Calling a Spring singleton JVM-global.
Assuming singleton means thread-safe.
Injecting a prototype once and expecting a new value per call.

What bean scopes does Spring provide, and when do they matter?

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