2021-05-03 09:46  阅读(134)
文章分类:Spring 入门教程 文章标签:SpringSpring 教程
©  原文作者:一点教程 原文地址:http://www.yiidian.com/spring/

可能会有这样一种情况,当你创建多个具有相同类型的 bean 时,并且想要用一个属性只为它们其中的一个进行装配,在这种情况下,你可以使用 @Qualifier 注解和 @Autowired 注解通过指定哪一个真正的 bean 将会被装配来消除混乱。下面是使用 @Qualifier 注解的一个示例。

一、编写Bean类

CustomerDao接口:

    
    package com.yiidian.dao;
    /**
     * 
     * @author http://www.yiidian.com
     *
     */
    public interface CustomerDao {
    	public void save();
    }
    

CustomerDaoMySQLImpl实现:

    
    package com.yiidian.dao.impl;
    
    import org.springframework.stereotype.Repository;
    
    import com.yiidian.dao.CustomerDao;
    /**
     * @author http://www.yiidian.com
     *
     */
    @Repository(value="customerDao1")
    public class CustomerDaoMySQLImpl implements CustomerDao {
    
    	@Override
    	public void save() {
    		System.out.println("customerDao的MySQL实现");
    	}
    	
    }
    

CustomerDaoOracleImpl实现类:

    
    package com.yiidian.dao.impl;
    
    import org.springframework.stereotype.Repository;
    
    import com.yiidian.dao.CustomerDao;
    /**
     * @author http://www.yiidian.com
     *
     */
    @Repository(value="customerDao2")
    public class CustomerDaoOracleImpl implements CustomerDao {
    
    	@Override
    	public void save() {
    		System.out.println("customerDao的Oracle实现");
    	}
    	
    }
    

CustomerService接口:

    
    package com.yiidian.service;
    /**
     * 
     * @author http://www.yiidian.com
     *
     */
    public interface CustomerService {
    
    	public void save();
    }
    

CustomerServiceImpl实现:

    
    package com.yiidian.service.impl;
    
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.stereotype.Service;
    
    import com.yiidian.dao.CustomerDao;
    import com.yiidian.service.CustomerService;
    /**
     * 
     * @author http://www.yiidian.com
     *
     */
    @Service(value="customerService")
    public class CustomerServiceImpl implements CustomerService {
    	@Autowired
    	private CustomerDao customerDao;
    
    	@Override
    	public void save() {
    		customerDao.save();
    	}
    }
    

二、配置applicationContext.xml

    
    <?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
    	xmlns:p="http://www.springframework.org/schema/p"
    	xmlns:context="http://www.springframework.org/schema/context"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="
            http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
            http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    	
    	<!-- 开启SpringIOC注解扫描 -->
    	<context:component-scan base-package="com.yiidian"></context:component-scan>
    	
    </beans>

三、编写测试类

    
    package com.yiidian.test;
    
    import org.junit.Test;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    import com.yiidian.service.CustomerService;
    /**
     * @author http://www.yiidian.com
     *
     */
    public class Demo1 {
    	
    	@Test
    	public void test1(){
    		ApplicationContext ac = new ClassPathXmlApplicationContext("applicationContext.xml");
    		CustomerService customerService = (CustomerService)ac.getBean("customerService");
    		customerService.save();
    	}
    }
    

四、运行之后,发现错误

运行测试类之后,发现后台报出以下错误:

No qualifying bean of type [com.yiidian.dao.CustomerDao] is defined: expected single matching bean but found 2: customerDao1,customerDao2

原因,CustomerServiceImpl尝试注入CustomerDao类型的对象,但是在IOC容器中存在两个CustomerDao接口的实现类对象,分别为CustomerDaoMySQLImpl和CustomerDaoOracleImpl,导致注入失败!

五、使用@Qualifier注解解决问题

在CustomerServiceImpl注入CustomerDao同时使用@Autowired和@Qualifier指定注入的对象名称。

    
    
    @Service(value="customerService")
    public class CustomerServiceImpl implements CustomerService {
    	@Autowired
    	@Qualifier("customerDao1")  //关键是@@Qualifier注解指定了名称
    	private CustomerDao customerDao;
    
    	@Override
    	public void save() {
    		customerDao.save();
    	}
    }
    

这时运行测试类,结果正确啦:

202105030946024018_1.png

源码下载:http://pan.baidu.com/s/1slwThRB

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