Spring @Qualifier 注解,一个service 接口,有多个实现时,如何在controller 只引入service 接口,进而实现引入具体bean

阳光穿透心脏的1/2处 2022-04-15 05:26 224阅读 0赞

参考: [https://blog.csdn.net/mazuyu408/article/details/79629846][https_blog.csdn.net_mazuyu408_article_details_79629846]

## @**Qualifier 作用** ##

在只引入service 接口的情况下在,指示spring 引入value 为那个别名的具体service 实现类

## 场景: ##

假设有一个场景,一个service 接口定义了多个 实现类,而在controller 我只想引入 service 接口,而这时,因为有个实现spring 不知道具体引入那个就会报错

接口;

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

实现1:起别名,标记为service

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

实现2:起别名,标记为service1

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

引入例子

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

## 产生的问题: ##

这样引入时的报错信息:提示 创建Bean EmployeeInfoControl失败,由于@autowired  employeeService失败,

没有类型\[com.test.service\]的唯一bean。定义:期望的单个匹配bean，但发现2:\[service1, service2\]

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]

##  解决办法: ##

前面我们不是分别给两个service实现类起了别名吗,这里实际要导入那个类型,(假设要导入的是,EmployeeServiceImpl 别名是service,可以将controller 修改如下

@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
        }
    }

或者使用@Resource 注解

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

[https_blog.csdn.net_mazuyu408_article_details_79629846]: https://blog.csdn.net/mazuyu408/article/details/79629846