java - Handling several implementations of one Spring bean/interface

Question

Say I need to rely on several implementations of a Spring bean. I have one AccountService interface and two implementations: DefaultAccountServiceImpl and SpecializedAccountServiceImpl.

1. How is this possible (injecting one or the other implementation) in Spring?

2. Which implementation will the following injection use?

   @Autowired
   private AccountService accountService;
   

Answer 1

Ad. 1: you can use @Qualifier annotation or autowire using @Resource as opposed to @Autowired which defaults to field name rather than type.

Ad. 2: It will fail at runtime saying that two beans are implementing this interface. If one of your beans is additionally annotated with @Primary, it will be preferred when autowiring by type.