Injecting Specific Service Implementations in Spring with @Autowired, @Qualifier, and @Resource

Spring provides several ways to inject a specific implementation of a service interface into a controller. This article describes three common approaches.

Method 1 : Use @Autowired together with @Qualifier("beanId") to specify which bean to inject.

public interface HumanService {
    String name();
}
@Service
public class TeacherServiceImpl implements HumanService {
    @Override
    public String name() {
        System.out.println("teacher");
        return "teacher";
    }
}
@Service
public class DoctorServiceImpl implements HumanService {
    @Override
    public String name() {
        System.out.println("doctor");
        return "doctor";
    }
}
@RestController
public class HumanController {
    @Autowired
    @Qualifier("teacherServiceImpl")
    private HumanService humanService;

    @RequestMapping("/name")
    public String name() {
        return humanService.name();
    }
}

Method 2 : Use @Resource(type = DoctorServiceImpl.class) (or @Resource(name="...")) to inject by type or name.

@RestController
public class HumanController {
    // @Resource(type = DoctorServiceImpl.class) // method 2
    @Autowired
    @Qualifier("teacherServiceImpl")
    private HumanService humanService;
    // ...
}

Method 3 : Define bean names in @Service("beanName") and inject them with @Resource(name="beanName").

@Service("teacherService")
public class TeacherServiceImpl implements HumanService { /* ... */ }
@Service("doctorService")
public class DoctorServiceImpl implements HumanService { /* ... */ }

@RestController
public class HumanController {
    @Resource(name="doctorService")
    private HumanService humanService;
    // ...
}

The article also explains that @Service registers the class as a bean, that @Autowired performs by‑type injection by default, while @Resource defaults to by‑name injection, and notes differences such as required‑attribute handling.