learn-co-curriculum / java-mod-6-bean-scope

Bean Scope

Learning Goals

• Define bean scope.
• Give an overview of the various bean scopes.

Introduction

The Spring container manages object instances (beans) which are automatically injected into various fields and parameters. We can define the scope of these beans, i.e., we can define when a bean is created, injected, and deleted. The default scope of a bean is singleton.

Different Bean Scopes

There are six bean scopes provided by Spring:

1. Singleton.
2. Prototype.
3. Request.
4. Session.
5. Application.
6. WebSocket.

The first two scopes (singleton and prototype) can be used in any Spring application but the next four are only available in web applications.

Singleton

This scope ensures that there is only a single bean created from each method. We don’t have to explicitly set a bean’s scope to singleton because it is the default. But we could do that using the @Scope annotation:

@Bean
@Scope("singleton")
public Dog dog() { ... }

Prototype

The prototype scope returns a new bean every time it has to be injected somewhere. We can define it like so:

@Bean
@Scope("prototype")
public Dog dog() { ... }

Request

This scope creates beans that are available for the entire lifecycle of an HTTP request. The request can be processed by several different components but they will all use the same bean.

Session

The beans created with this scope are available for the entire HTTP session that may have multiple HTTP requests with the same cookies or session IDs.

Application

This enables a broader scope than the singleton scope which is scoped to a single application. The application scope makes the beans available for all applications running in the same ServletContext.

WebSocket

This enables beans to be created and available during a full WebSocket session cycle.

Conclusion

We have looked at how to define bean behavior by changing their scope. The singleton scope is the default but for web applications we will use the request and session scopes pretty often.

Reference

• Bean Scopes Docs