Spring创建原型bean两次？

Question

I have a simple spring boot app with the following config:

@Configuration
public class MyConfig {
    @Bean
    @Scope(value = "prototype", proxyMode = ScopedProxyMode.TARGET_CLASS)
    public HashMap<String, BidAskPrice> beanyBoi() {
        System.out.println("creating a new one");
        return dataFetcher().getPairPricesBidAsk();
    }
}

and i have a service

@Service
public class ProfitCalculatorService {

  @Autowired
  private HashMap<String, BidAskPrice> prices;

  public HashMap<String, BidAskPrice> getPrices() {
    return prices;
  }
}

and i have a controller

@RestController
public class TestController {

  @Autowired
  ProfitCalculatorService profitCalculatorService;

  @GetMapping("/getprices")
    public HashMap<String, BidAskPrice> someprices() {
      return profitCalculatorService.getPrices();
    }
  }
}

now when i hit the /getprices endpoint, i was seeing some odd behaviour. The following message is logged twice: "creating a new one".

Answer 1

Your beans have a prototype scope, it means that every time that you asked for this bean a new instance will be created.

Official explanation:

The non-singleton prototype scope of bean deployment results in the creation of a new bean instance every time a request for that specific bean is made. That is, the bean is injected into another bean or you request it through a getBean() method call on the container. As a rule, you should use the prototype scope for all stateful beans and the singleton scope for stateless beans.

https://docs.spring.io/spring/docs/current/spring-framework-reference/core.html#beans-factory-scopes-prototype

Another thing is the proxyMode with TARGET_CLASS value. It means that the bean injected into the ProfitCalculatorService is not the BidAskPrice itself, but a proxy to the bean (created using CGLIB) and this proxy understands the scope and returns instances based on the requirements of the scope (in your case prototype).

So, my suggestion is: You don't need to create an explicitly bean of HashMap<String, BidAskPrice> . Since BidAskPrice is a bean, you can inject the HashMap<String, BidAskPrice> directly in your service, Spring will manage this list for you!