Spring Bean Scopes

Question

Can someone explain what the scopes are in Spring beans I\'ve always just used \'prototype\' but are there other parameters I can put in place of that?

Example of wh

Answer 1

In Spring, bean scope is used to decide which type of bean instance should be returned from Spring container back to the caller.

5 types of bean scopes are supported :

1. Singleton : It returns a single bean instance per Spring IoC container.This single instance is stored in a cache of such singleton beans, and all subsequent requests and references for that named bean return the cached object.If no bean scope is specified in bean configuration file, default to singleton.

2. Prototype : It returns a new bean instance each time when requested. It does not store any cache version like singleton.

3. Request : It returns a single bean instance per HTTP request.

4. Session : It returns a single bean instance per HTTP session (User level session).

5. GlobalSession : It returns a single bean instance per global HTTP session. It is only valid in the context of a web-aware Spring ApplicationContext (Application level session).

In most cases, you may only deal with the Spring’s core scope – singleton and prototype, and the default scope is singleton.

Answer 2

A short example what is the difference between @Scope("singleton") (default) and @Scope("prototype"):

DAO class:

package com.example.demo;

public class Manager {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Configuration:

@Configuration
public class AppConfiguration {
    @Bean
    @Scope("singleton")
    public Manager getManager(){
        return new Manager();
    }
}

and MainApp:

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
        context.scan("com.example.demo");
        context.refresh();

        Manager firstManager = context.getBean(Manager.class);
        firstManager.setName("Karol");

        Manager secondManager = context.getBean(Manager.class);
        System.out.println(secondManager.getName());
    }

}

In this example the result is: Karol even if we set this name only for firstManager object. It's because Spring IoC container created one instance of object. However when we change scope to @Scope("prototype") in Configuration class then result is: null because Spring IoC container creates a new bean instance of the object when request for that bean is made.

Answer 3

The Spring documentation describes the following standard scopes:

singleton: (Default) Scopes a single bean definition to a single object instance per Spring IoC container.

prototype: Scopes a single bean definition to any number of object instances.

request: Scopes a single bean definition to the lifecycle of a single HTTP request; that is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.

session: Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.

global session: Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.

Additional custom scopes can also be created and configured using a CustomScopeConfigurer. An example would be the flow scope added by Spring Webflow.

By the way, you argues that you always used prototype what I find strange. The standard scope is singleton and in the application I develop, I rarely need the prototype scope. You should maybe take a look at this.

Answer 4

About prototype bean(s) :

The client code must clean up prototype-scoped objects and release expensive resources that the prototype bean(s) are holding. To get the Spring container to release resources held by prototype-scoped beans, try using a custom bean post-processor, which holds a reference to beans that need to be cleaned up.

ref : https://docs.spring.io/spring/docs/3.0.0.M3/reference/html/ch04s04.html#beans-factory-scopes-prototype

Answer 5

Detailed explanation for each scope can be found here in Spring bean scopes. Below is the summary

Singleton - (Default) Scopes a single bean definition to a single object instance per Spring IoC container.

prototype - Scopes a single bean definition to any number of object instances.

request - Scopes a single bean definition to the lifecycle of a single HTTP request; that is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.

session - Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.

global session - Scopes a single bean definition to the lifecycle of a global HTTP Session. Typically only valid when used in a portlet context. Only valid in the context of a web-aware Spring ApplicationContext.

Answer 6

Also websocket scope is added:

Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext.

As the per the content of the documentation, there is also thread scope, that is not registered by default.