springboot-注解：@Qualifier

 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：

有如下接口：

package com.xi.springbootdemo.qualifier;

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

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

package com.xi.springbootdemo.qualifier;

import org.springframework.stereotype.Service;

@Service("service")
public class EmployeeServiceImpl implements EmployeeService{
    @Override
    public String getEmployeeById(Long id) {
        return "0";
    }
}

package com.xi.springbootdemo.qualifier;

import org.springframework.stereotype.Service;

@Service("service1")
public class EmployeeServiceImpl1 implements EmployeeService{
    @Override
    public String getEmployeeById(Long id) {
        return "1";
    }
}

调用代码如下：

package com.xi.springbootdemo.qualifier;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@RestController
public class EmployeeInfoControl {
    @Autowired
    private EmployeeService employeeService;

    @RequestMapping("/emplayee.do")
    public void showEmplayeeInfo(){
        String employeeById = employeeService.getEmployeeById(1l);
        System.out.println("employeeById值为"+employeeById);
    }
}

在启动时报如下错误：
 

Field employeeService in com.xi.springbootdemo.qualifier.EmployeeInfoControl required a single bean, but 2 were found:
	- service: defined in file [F:\DaoEclipseWorkplace\springbootdemo\target\classes\com\xi\springbootdemo\qualifier\EmployeeServiceImpl.class]
	- service1: defined in file [F:\DaoEclipseWorkplace\springbootdemo\target\classes\com\xi\springbootdemo\qualifier\EmployeeServiceImpl1.class]


Action:

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：

package com.xi.springbootdemo.qualifier;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Conditional;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@RestController
public class EmployeeInfoControl {
    @Autowired
    @Qualifier("service")
    private EmployeeService employeeService;

    @RequestMapping("/emplayee.do")
    public void showEmplayeeInfo(){
        String employeeById = employeeService.getEmployeeById(1l);
        System.out.println("employeeById值为"+employeeById);
    }
}

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