Spring的注解@Qualifier应用

最近在项目开发中用到Spring的注解@Qualifier

场景1 应用

应用场景：如下类

public abstract class AbstractEventSerivceImpl<T> {
    。。。。。。。。。。。。。。。
    }

同时下面几个类都继承了上面的类

@Service("orderPayStatusEventService")
public class OrderPayStatusEventServiceImpl extends AbstractEventSerivceImpl<PayStatusEvent> implements IHandlerEventService {

}

@Service("orderReviewStatusEventService")
public class OrderReviewStatusEventServiceImpl extends AbstractEventSerivceImpl<OrderReviewStatusEvent> implements IHandlerEventService {

    }

调用代码如下：

public class PayStatusEventReceiver {
    @Autowired
    @Qualifier("orderPayStatusEventService")
    IHandlerEventService orderPayStatusEventService;
    public void eventReceived(EventTrackerEntity  eventTrackerEntityStr){    
            orderPayStatusEventService.saveEventTracer(eventTrackerEntityStr);

}

场景2 应用

有如下接口：

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

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
    }
}