有如下接口：

public interfaceEmployeeService {publicEmployeeDto getEmployeeById(Long id);

}

同时有下述两个实现类 EmployeeServiceImpl和EmployeeServiceImpl1：

@Service("service")public class EmployeeServiceImpl implementsEmployeeService {publicEmployeeDto getEmployeeById(Long id) {

return newEmployeeDto();

}

}

@Service("service1")public class EmployeeServiceImpl1 implementsEmployeeService {publicEmployeeDto getEmployeeById(Long id) {

return newEmployeeDto();

}

}

调用代码如下：

@Controller

@RequestMapping("/emplayee.do")public classEmployeeInfoControl {

@Autowired

EmployeeService employeeService;

@RequestMapping(params= "method=showEmplayeeInfo")public voidshowEmplayeeInfo(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 classEmployeeInfoControl {

@Autowired

@Qualifier("service")

EmployeeService employeeService;

@RequestMapping(params= "method=showEmplayeeInfo")public voidshowEmplayeeInfo(HttpServletRequest request, HttpServletResponse response, EmployeeDto dto) {

#略

}

}