@Qualifier注解的使用

朴灿烈づ我的快乐病毒、 2022-12-02 01:19 170阅读 0赞

@Qualifier这个注解很简单。就是你一个接口有多个实现类。在Spring中使用了 @Autowired自动注入的时候不知道怎么选择是哪个具体的实现类了。  
例如UserDao有2个实现类。  
\*\*![加粗样式][20200829100921204.png_pic_center]  
\*\*  
如果你是Spring容器，给你一个UserDao接口，你知道在运行的时候使用那个实现类吗。所以使用@Qualifier来具体指向一下即可。这样对于接口的扩展十分有利。  
我们具体看看代码吧

package com.zxf.test1;
    public class User { 
        private String name;
        private String pwd;
    
        public String getName() { 
            return name;
        }
    
        public void setName(String name) { 
            this.name = name;
        }
    
        public String getPwd() { 
            return pwd;
        }
    
        public void setPwd(String pwd) { 
            this.pwd = pwd;
        }
    }

package com.zxf.test1;
    public interface UserDao { 
        public User getUserByName(String u);
    }

package com.zxf.test1;
    import org.springframework.stereotype.Component;
    @Repository("uu")
    public class UserDaoImpl implements UserDao { 
        @Override
        public User getUserByName(String u) { 
            System.out.println("uu用户查找中。。。");
            return new User();
        }
    }

package com.zxf.test1;
    import org.springframework.stereotype.Component;
    @Repository("umysql")
    public class UserDaoMysqlImpl implements UserDao { 
        @Override
        public User getUserByName(String u) { 
            System.out.println("mysql用户查找中。。。");
            return new User();
        }
    }

package com.zxf.test1;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.beans.factory.annotation.Qualifier;
    import org.springframework.stereotype.Component;
    @Service
    public class My1Service { 
        @Autowired
        /* 可以在这里修改选择使用那个相同接口的不同实现类。 */
        @Qualifier("uu")
        //@Qualifier("umysql")
        UserDao userDao;
        public User login(String u,String p){ 
            System.out.println("Service 接受到请求，开始处理。");
           return userDao.getUserByName(u);
        }
    }

package com.zxf.test1;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Component;
    @Controller("mycon1")
    public class My1Controller { 
        @Autowired
        My1Service my1Service;
        public String list(){ 
            String name="zhang3";
            String pwd="123";
            User user=my1Service.login(name,pwd);
            if(user!=null){ 
                System.out.println("Hello:"+name);
                return "登录OK";
            }else { 
                return "登录失败";
            }
        }
    }

package com.zxf.test1;
    
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class Main1 { 
        public static void main(String[] args) { 
            ApplicationContext app=new ClassPathXmlApplicationContext("Spring1.xml");
            My1Controller bean = app.getBean("mycon1", My1Controller.class);
             String info=bean.list();
             System.out.println(info);
        }
    }

Spring1.xml

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xmlns:context="http://www.springframework.org/schema/context"
           xmlns:aop="http://www.springframework.org/schema/aop"
           xsi:schemaLocation="
            http://www.springframework.org/schema/context
            http://www.springframework.org/schema/context/spring-context.xsd
             http://www.springframework.org/schema/aop
              http://www.springframework.org/schema/aop/spring-aop.xsd
            http://www.springframework.org/schema/beans
            http://www.springframework.org/schema/beans/spring-beans.xsd">
        <context:component-scan base-package="com.zxf"/>
    </beans>

[20200829100921204.png_pic_center]: /images/20221123/738cd7d127f5413a957459f3bc86d66f.png