Spring5

Spring provides a powerful and flexible way to choose and control the scope of the objects created from a given bean definition.
There are total 6 scopes supported by Spring Framework. Out of the these 4 of them are available only if you use a web-aware
ApplicationContext

Singleton scope

This is the default scope for all the beans in Spring unless you explicitly specify a different scope. Spring creates only a single shared instance for all the requests for a bean definition.

Spring creates and caches all such singleton scope beans and subsequent requests get fulfilled from the cache. Please note that concept of Spring Singleton beans is different from the Singleton pattern from the GoF(Gang of Four). In GoF Singleton the scope of the singleton object is one instance per ClassLoader, however in the spring it is one instance per IoC container and per bean.

This is how you define a bean with singleton scope using XML based configuration:

Prototype scope

With Prototype scope, a new instance is created using the bean definition every time there is a new request for a specific bean.

The following example defines a bean as a prototype in XML:

Request scope

In request scope, Spring container will create a new instance for each new HTTP request. Changes to the state of a particular instance of Request scoped object will not be visible to other instances of the same bean definition. Once request lifecycle is complete these request scoped objects will be discarded by Spring container.

The following example defines a bean as a Request Scope in XML:

The following example shows java based configuration on how to assign the request scope using @RequestScope annotation:

@RequestScope
@Component
public class RequestAction {
    // ...
}

Session scope

In Session scope, Spring container will create a new instance for each new HTTP Session. Changes to the state of a particular instance in one session will not be visible to other sessions. Once session terminates objects will be discarded by Spring container.

The following example defines a bean as a Request Scope in XML:

The following example shows java based configuration on how to assign the request scope using @SessionScope annotation:

@SessionScope
@Component
public class UserConfig {
    // ...
}

Application scope

When using Application scope, Spring container will create a single instance of a bean for entire web application context. The instance will be stored as ServletContext. It is like a Singleton per ServletContext instead of per ApplicationContext Once session terminates objects will be discarded by Spring container.

The following example defines a bean as an Application Scope in XML:

The following example shows java based configuration on how to assign the request scope using @SessionScope annotation:

@ApplicationScope
@Component
public class ApplicationPreferences {
    // ...
}

WebSocket scope

Websocket scoped beans are more like the singleton scoped beans and stay longer than the individual WebSocket session.

The following example defines a bean as a WebSocket Scope in XML:

The following example shows java based configuration on how to assign the request scope using @WebSocket annotation:

@WebSocket
@Component
public class MyBean {
    // ...
}

Custom Spring Beans Scope

The Spring bean scope mechanism is extensible. It allows defining custom scopes and redefining existing ones except from the singleton and prototype scopes.

Following example shows how to use the SimpleThreadScope.This is already included in Spring framework but not registered by default. To use this scope, We need to first register the scope with the container using the CustomScopeConfigurer class.

Since we have scoped the bean at Thread scope, same instance of bean will be returned for each request made by a single thread.

The following example defines a bean with thread Scope in XML:

The following example shows java based configuration on how to assign the request scope using @WebSocket annotation:

@Component
@Scope("thread")
public class MyBean {
}

Summary

In this article we had an overview of all the possible Spring Bean Scopes. This is an important Spring interview question, one should be comfortable in choosing the correct scope for a particular requirement. Which Please leave your comments below in case you have any questions or you find any correction in above content.

More Resources available at :

Scope – Spring Docs
Spring Tutorials