how to get multiple instances of same bean in spring?

Question

By default, spring beans are singletons. I am wondering if there is a way to get multiple instances of same bean for processing.

Here is what I do currently

    @Configuration
    public class ApplicationMain { 

     @Value("${service.num: not configured}")
    private int num;

    //more code

@PostConstruct
public void run(){

        for (int i = 0; i < num ; i++) {
                    MyService ser = new MyService(i);
                    Future<?> tasks = executor.submit(ser);
                }

    }
}

Here is the Service class

    public class MyService implements Runnable {

    private String name;

    public Myservice(int i){

    name=String.ValueOf(i);

    }
  }

I have simplified my usecase here. I want to have MyService as spring bean and get as many as possible based on configuartion (which is num) in the above for-loop? wondering how that is possible.

Thanks

Answer 1

First you'll have to make MyService a Spring bean. You can do this by annotating the class with @Component. Next, as you say, Spring beans are Singletons by default, so this can be changed with one more annotation - @Scope("prototype").

A prototype bean scope means that each time you ask Spring for an instance of the bean, a new instance will be created. This applies to Autowiring, asking the application context for the bean with getBean(), or using a bean factory.

Answer 2

Here is a simple example of how to register a desired number of beans of the same type

@Configuration
public class MultiBeanConfig implements ApplicationContextAware {

    @Value("${bean.quantity}")
    private int quantity;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        for (int i = 0; i < quantity; i++) {
            ((ConfigurableApplicationContext)applicationContext).getBeanFactory()
                    .registerSingleton("my-service-" + i, new MyService());
        }
        assert(applicationContext.getBeansOfType(MyService.class).size() == quantity);
    }

    class MyService {

    }
}