Spring Bean Scopes (Singleton vs Prototype)

Detailed Explanation of Bean Scopes

By default, every bean registered in the Spring IoC Container is a Singleton. Spring creates exactly one instance of the bean per container and injects that same shared instance everywhere.

Supported Spring Bean Scopes:

• Singleton (Default): One single bean instance per Spring IoC container. State must be thread-safe!
• Prototype: A new instance is created every time the bean is requested from the container.
• Request (Web): A new instance per HTTP request lifecycle.
• Session (Web): A new instance per HTTP Session lifecycle.
• Application (Web): One instance per ServletContext lifecycle.

Production Code Example:

package com.anujsingh.digitalguru.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import com.anujsingh.digitalguru.model.ShoppingCart;

@Configuration
public class AppConfig {

    @Bean
    @Scope(ConfigurableBeanFactory.SCOPE_PROTOTYPE)
    public ShoppingCart shoppingCart() {
        return new ShoppingCart();
    }
}

Key Architectural Concepts & Best Practices:

When working with Spring Bean Scopes (Singleton vs Prototype) in enterprise Spring Boot applications, keep these key architectural guidelines in mind:

• Separation of Concerns: Maintain a strict boundary between HTTP endpoints, service logic, and database persistence layers.
• Framework Conventions: Rely on Spring Boot auto-configuration defaults whenever possible, overriding settings only via application.yml or @Configuration classes when customized behavior is required.
• Production Monitoring & Reliability: Ensure proper exception handling, thread-safety, and resource cleanup to prevent memory leaks and unexpected runtime downtime.
• Developer Ergonomics: Write clean, self-documenting code with modern Java features (Records, Lambdas, Streams) to simplify code reviews and maintenance.

Summary Takeaway:

Mastering Spring Bean Scopes (Singleton vs Prototype) ensures that your Java & Spring Boot backend microservices remain maintainable, secure, and compliant with modern enterprise software engineering standards.