說明下場景,代碼如下：

有如下接口：

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

同時有下述兩個實現類 EmployeeServiceImpl和EmployeeServiceImpl1：

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

@Service("service1")
public class EmployeeServiceImpl1 implements EmployeeService {
    public EmployeeDto getEmployeeById(Long id) {
        return new EmployeeDto();
    }
}

調用代碼如下：

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

在啟動tomcat時報如下錯誤：

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]

其實報錯信息已經說得很明確了,在autoware時，由於有兩個類實現了EmployeeService接口，所以Spring不知道應該綁定哪個實現類，所以拋出了如上錯誤。

這個時候就要用到@Qualifier註解了，qualifier的意思是合格者，通過這個標示，表明了哪個實現類才是我們所需要的，我們修改調用代碼，添加@Qualifier註解，需要註意的是@Qualifier的參數名稱必須為我們之前定義@Service註解的名稱之一！

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

轉載自：https://www.cnblogs.com/smileLuckBoy/p/5801678.html

Spring的註解@Qualifier小結