Following example shows that singleton bean is created only once per Spring container.

Example

A singleton bean

package com.logicbig.example;

public class ServiceBean {

}

Other beans injecting singleton bean

package com.logicbig.example;


import org.springframework.beans.factory.annotation.Autowired;

public class ClientBean1 {
  @Autowired
  private ServiceBean serviceBean;

  public void doSomething(){
      System.out.println("from ClientBean1: serviceBean: "+System.identityHashCode(serviceBean));
  }
}

package com.logicbig.example;


import org.springframework.beans.factory.annotation.Autowired;

public class ClientBean2 {
  @Autowired
  private ServiceBean serviceBean;

  public void doSomething(){
      System.out.println("from ClientBean2: serviceBean: "+System.identityHashCode(serviceBean));
  }
}

Defining beans and running example app

package com.logicbig.example;

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

public class AppMain {

  @Scope(ConfigurableBeanFactory.SCOPE_SINGLETON)
  @Bean
  public ServiceBean serviceBean(){
      return new ServiceBean();
  }

  @Bean
  public ClientBean1 clientBean1(){
      return new ClientBean1();
  }

  @Bean
  public ClientBean2 clientBean2(){
      return new ClientBean2();
  }

  public static void main(String[] args) {
      runApp();
      runApp();
  }

  private static void runApp() {
      System.out.println("--- running app ---");
      AnnotationConfigApplicationContext context =
              new AnnotationConfigApplicationContext(AppMain.class);
      context.getBean(ClientBean1.class).doSomething();
      context.getBean(ClientBean2.class).doSomething();
  }
}

Output

--- running app ---
from ClientBean1: serviceBean: 2132083608
from ClientBean2: serviceBean: 2132083608
--- running app ---
from ClientBean1: serviceBean: 1423108099
from ClientBean2: serviceBean: 1423108099

We created the spring context twice to show that Spring singleton beans have different instance in different spring context (container), so they are not JVM level singletons.

Example Project

Dependencies and Technologies Used:

• spring-context 4.2.3.RELEASE: Spring Context.
• JDK 1.8
• Maven 3.6.3