Spring No unique bean of type

问题:

i have a little trouble in Spring with two component of a service.

I have this component:

@Component
public class SmartCardWrapper 

and this one:

@Component
public class DummySmartCardWrapper extends SmartCardWrapper

The service autowire both but spring fails due this expection:

org.springframework.beans.factory.NoSuchBeanDefinitionException: No unique bean of type [com.cinebot.smartcard.SmartCardWrapper] is defined: expected single matching bean but found 2: [dummySmartCardWrapper, smartCardWrapper]

Why it doesn't use class names?

回答1:

That's one of the most basic concepts of Spring - Inversion of Control.

You don't need to declare your dependencies using their implementation types (to avoid coupling with implementation). You can declare them using interfaces or superclasses instead, and make Spring find the proper implementation class in the context.

In other words, bean are not distinguished by their implementation classes, because you may want to change implementation class of a bean without changing the beans that depend on it. If you want to distinguish between different beans of the same type, use logical bean names instead:

@Autowired @Qualifier("smartCardWrapper")
private SmartCardWrapper smardCardWrapper;

@Autowired @Qualifier("dummySmartCardWrapper")
private SmartCardWrapper dummySmardCardWrapper;