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Bean Scopes

Basic Spring
≈ 2 min read

How many instances of one bean the application needs

A scope determines how the container creates bean instances and how long they live. The two main scopes to understand in Spring Core are singleton and prototype.

By default, a bean has the singleton scope: within one ApplicationContext, Spring normally uses the same instance of that bean. 

@Component
@Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
class ReportDraft {
}

prototype has a different idea: every request for that bean from the container causes a new instance to be created. This is useful when one managed object should not be shared between independent operations.

A Spring singleton is not a global Singleton

A Spring singleton does not mean “exactly one object in the whole JVM.” The boundary is a particular container. If you create two independent ApplicationContext instances, each can have its own singleton bean instance.

A scope does not make state automatically safe. A singleton bean is often used by many parts of the application at the same time. That is why storing mutable state for a particular request or operation inside it is usually a bad idea.

In web applications, Spring also provides scopes tied to an HTTP request and session. They will make more sense when we move to Spring MVC; for Spring Core, it is enough to confidently distinguish singleton and prototype.

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