Spring的注解@Qualifier小结

有以下接口：

public interface EmployeeService {
    public EmployeeDto getEmployeeById(Long id);
}

有两个实现类：

@Service("service")
public class EmployeeServiceImpl implements EmployeeService {
    public EmployeeDto getEmployeeById(Long id) {
        return new EmployeeDto();
    }
}

@Service("service1")
public class EmployeeServiceImpl implements EmployeeService {
    public EmployeeDto getEmployeeById(Long id) {
        return new EmployeeDto();
    }
}

调用方法为：

@Controller
@RequestMapping("/emplayee")
public class EmployeeInfoControl {
   
    @Autowired
    EmployeeService employeeService;
     
    @RequestMapping(params = "method=showEmplayeeInfo")
    public void showEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) {
        #略
    }
}

报错

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'employeeInfoControl': 
Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: 
Could not autowire field: com.test.service.EmployeeService com.test.controller.EmployeeInfoControl.employeeService; 
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: 
No unique bean of type [com.test.service.EmployeeService] is defined: expected single matching bean but found 2: [service1, service2]

很明显了,在autoware时，由于有两个类实现了EmployeeService接口，所以Spring不知道应该绑定哪个实现类，所以抛出了如上错误。

这个时候就要用到@Qualifier注解了，qualifier的意思是合格者。通过这个标示，表明了哪个实现类才是我们所需要的，我们修改调用代码，添加@Qualifier注解，需要注意的是@Qualifier的参数名称必须为我们之前定义@Service注解的名称之一。

@Controller
@RequestMapping("/emplayee")
public class EmployeeInfoControl {
    
    @Autowired
    @Qualifier("service")
    EmployeeService employeeService;
    
    @RequestMapping(params = "method=showEmplayeeInfo")
    public void showEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) {
        #略
    }
}