Spring的注解@Qualifier小结

Bertha 。 2022-06-04 07:15 184阅读 0赞

Spring的注解@Qualifier小结  
近期在捯饬spring的注解，现将遇到的问题记录下来，以供遇到同样问题的童鞋解决~  
先说明下场景,代码如下：

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

有如下接口：

同时有下述两个实现类 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();
        }
    }

调用代码如下：

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

在启动tomcat时报如下错误：

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]

其实报错信息已经说得很明确了,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.do")public class EmployeeInfoControl { 
    
        @Autowired
        @Qualifier("service")
        EmployeeService employeeService;
    
        @RequestMapping(params = "method=showEmplayeeInfo")
        public void showEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) {
            #略
        }
    }