Spring @Scope annotation with Singleton Scope Example

In this article, we will discuss how to create a bean, scoped as a singleton, using the @Scope annotation.

We use @Scope to define the scope of a @Component class or a @Bean definition.

When a Spring bean is scoped as a singleton, the Spring IoC container creates exactly one instance of the object defined by that bean definition.

 
By default, the Spring IoC container creates and initializes all beans as a singleton. But we can define the scope of a bean as a singleton using the scope="singleton" attribute of the element or using the @Scope(value = ConfigurableBeanFactory.SCOPE_SINGLETON) annotation.

YouTube Video - Spring @Scope Annotation

 We will demonstrate this example using Annotation based (@Component) as well as Java-based configuration(@Bean). 

Spring @Scope Annotation + Singleton Scope + @Component Example

Let's create an example to demonstrate the usage of use @Scope annotation with a singleton scope in a spring application. 

Create a Simple Maven Project

Create a simple maven project using your favorite IDE and refer below section for packaging structure. If you are new to maven then read this article How to Create a Simple Maven Project.

Project Structure

The below diagram shows a project structure for your reference - 

The pom.xml File

Note that Spring framework 6 required Java 17 or later version:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>learn-spring-framework</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
    </properties>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>6.0.4</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>6.0.4</version>
        </dependency>

    </dependencies>
</project>

MessageService.java

Next, let's create a MessageService interface as follows.

package net.javaguides.spring.scope;

public interface MessageService {

    String getMessage();

    void setMessage(String message);
}

Let's create TwitterMessageService class which implements the MessageService interface.

TwitterMessageService.java

package net.javaguides.spring.scope;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

@Component
@Scope(value = ConfigurableBeanFactory.SCOPE_SINGLETON)
public class TwitterMessageService implements MessageService {

    private String message;

    @Override
    public String getMessage() {
        return message;
    }

    @Override
    public void setMessage(String message) {
        this.message = message;
    }
}

Annotation-Based Configuration - AppConfig.java

package net.javaguides.spring.scope;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan(basePackages = "net.javaguides.spring")
public class AppConfig {
 
}

@ComponentScan annotation scans all beans whose class is annotated by the @Component annotation in a package specified by basePackages attribute. 

Running Spring Application - Application.java

Let's create a main class and run an application.

package net.javaguides.spring.scope;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Application {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext  context = new AnnotationConfigApplicationContext(AppConfig.class);
        MessageService messageService = context.getBean(MessageService.class);
        messageService.setMessage("TwitterMessageService Implementation");
        System.out.println(messageService.getMessage());
  
        MessageService messageService1 = context.getBean(MessageService.class);
        System.out.println(messageService1.getMessage());
        context.close();
    }
}

Output

TwitterMessageService Implementation
TwitterMessageService Implementation

Let's develop the same example using Java-based configuration with @Bean annotation. 

Spring @Scope Annotation + Singleton Scope + @Bean Example

MessageService.java

package net.javaguides.spring.scope;

public interface MessageService {

    String getMessage();

    void setMessage(String message);
}

Let's create TwitterMessageService class which implements the MessageService interface. 

TwitterMessageService.java

package net.javaguides.spring.scope;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

public class TwitterMessageService implements MessageService {

    private String message;

    @Override
    public String getMessage() {
        return message;
    }

    @Override
    public void setMessage(String message) {
        this.message = message;
    }
}

Java-based Configuration - AppConfig.java

Declare the above beans in java based configuration class.

package net.javaguides.spring.scope;

import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

@Configuration
public class AppConfig {

    @Bean
    @Scope(value = ConfigurableBeanFactory.SCOPE_SINGLETON)
    public MessageService messageService() {
        return new TwitterMessageService();
    }
}

Running Spring Application - Application.java

Let's create a main class and run an application.

package net.javaguides.spring.scope;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Application {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext  context = new AnnotationConfigApplicationContext(AppConfig.class);
        MessageService messageService = context.getBean(MessageService.class);
        messageService.setMessage("TwitterMessageService Implementation");
        System.out.println(messageService.getMessage());
  
        MessageService messageService1 = context.getBean(MessageService.class);
        System.out.println(messageService1.getMessage());
        context.close();
    }
}

Output

TwitterMessageService Implementation
TwitterMessageService Implementation

The source code of this article is available on my GitHub repository https://github.com/RameshMF/spring-core-tutorial

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