Singleton vs prototype

Definition

A singleton bean (the default) is created once and shared by everyone, so it must not hold per-request state. A prototype bean is created fresh every time it is requested.

Example code

The same instance, or a new one each time

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Scope;

class Counter { }

@Configuration
class AppConfig {
    @Bean
    Counter shared() { return new Counter(); }                 // singleton by default

    @Bean
    @Scope("prototype")
    Counter fresh() { return new Counter(); }                  // a new object on every request
}

class Demo {
    public static void main(String[] args) {
        try (var context = new AnnotationConfigApplicationContext(AppConfig.class)) {
            System.out.println("singleton same? " + (context.getBean("shared") == context.getBean("shared")));
            System.out.println("prototype same? " + (context.getBean("fresh") == context.getBean("fresh")));
        }
    }
}

// Output:
// singleton same? true
// prototype same? false