Conditions in Spring IoC container

Do I have any known way to inject beans in spring IoC container based on some condition. E.g. I have two beans:

<bean id="aaa" class="My"/>
<bean id="bbb" class="My"/>

... and want inject it in another bean based on开发者_如何学Python following rule:

Inject "aaa" if "aaa" isn't null or inject "bbb" in other case

Thanks

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You can use JavaConfig - there you can use java code to implement this logic. I've never used it, but taking an example from the docs:

@Configuration
public class ServiceConfig {
  private @Resource(name="aaa") Aaa aaa;
  private @Resource(name="bbb") Aaa bbb;

  public @Bean TransferService transferService() {
      TransferService service = new TransferServiceImpl();
      if (aaa != null) {
          service.setProperty(aaa);
      } else {
          service.setProperty(bbb);
      }
      return service;
  }
}

Another option is to use a FactoryBean to encapsulate that logic - the factory bean can lookup a bean in the context, and if found - return it. If not found - lookup another bean.

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If you are on spring 3.0 this can be achieved using SpEL - Expression langauge support.