Spring @Primary

Sometimes we need to define multiple beans of the same type. In these cases, the injection will be unsuccessful because Spring has no clue which bean we need.

方案1：@Qualifier
方案2：@Primary

@Component
@Primary
class Car implements Vehicle {}

@Component
class Bike implements Vehicle {}

@Component
class Driver {
    @Autowired
    Vehicle vehicle;
}

@Component
class Biker {
    @Autowired
    @Qualifier("bike")
    Vehicle vehicle;
}