springboot-注解：@Qualifier

有如下接口：

1. package com.xi.springbootdemo.qualifier;

2.  

3. public interface EmployeeService {

4. public String getEmployeeById(Long id);

5. }

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

1. package com.xi.springbootdemo.qualifier;

2.  

3. import org.springframework.stereotype.Service;

4.  

5. @Service("service")

6. public class EmployeeServiceImpl implements EmployeeService{

7. @Override

8. public String getEmployeeById(Long id) {

9. return "0";

10. }

11. }

1. package com.xi.springbootdemo.qualifier;

2.  

3. import org.springframework.stereotype.Service;

4.  

5. @Service("service1")

6. public class EmployeeServiceImpl1 implements EmployeeService{

7. @Override

8. public String getEmployeeById(Long id) {

9. return "1";

10. }

11. }

调用代码如下：

1. package com.xi.springbootdemo.qualifier;

2.  

3. import org.springframework.beans.factory.annotation.Autowired;

4. import org.springframework.context.annotation.Conditional;

5. import org.springframework.stereotype.Controller;

6. import org.springframework.web.bind.annotation.RequestMapping;

7. import org.springframework.web.bind.annotation.RestController;

8.  

9. import javax.servlet.http.HttpServletRequest;

10. import javax.servlet.http.HttpServletResponse;

11.  

12. @RestController

13. public class EmployeeInfoControl {

14. @Autowired

15. private EmployeeService employeeService;

16.  

17. @RequestMapping("/emplayee.do")

18. public void showEmplayeeInfo(){

19. String employeeById = employeeService.getEmployeeById(1l);

20. System.out.println("employeeById值为"+employeeById);

21. }

22. }

在启动时报如下错误：
 

1. Field employeeService in com.xi.springbootdemo.qualifier.EmployeeInfoControl required a single bean, but 2 were found:

2. - service: defined in file [F:\DaoEclipseWorkplace\springbootdemo\target\classes\com\xi\springbootdemo\qualifier\EmployeeServiceImpl.class]

3. - service1: defined in file [F:\DaoEclipseWorkplace\springbootdemo\target\classes\com\xi\springbootdemo\qualifier\EmployeeServiceImpl1.class]

4.  
5.  

6. Action:

7.  

8. Consider marking one of the beans as @Primary, updating the consumer to accept multiple beans, or using @Qualifier to identify the bean that should be consumed

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！

代码如下：

1. package com.xi.springbootdemo.qualifier;

2.  

3. import org.springframework.beans.factory.annotation.Autowired;

4. import org.springframework.beans.factory.annotation.Qualifier;

5. import org.springframework.context.annotation.Conditional;

6. import org.springframework.stereotype.Controller;

7. import org.springframework.web.bind.annotation.RequestMapping;

8. import org.springframework.web.bind.annotation.RestController;

9.  

10. import javax.servlet.http.HttpServletRequest;

11. import javax.servlet.http.HttpServletResponse;

12.  

13. @RestController

14. public class EmployeeInfoControl {

15. @Autowired

16. @Qualifier("service")

17. private EmployeeService employeeService;

18.  

19. @RequestMapping("/emplayee.do")

20. public void showEmplayeeInfo(){

21. String employeeById = employeeService.getEmployeeById(1l);

22. System.out.println("employeeById值为"+employeeById);

23. }

24. }

问题解决，用浏览器访问：

http://localhost:8080/emplayee.do

打印日志如下：

employeeById值为0