1_使用Mapper代理方式实现查询

短命女 2023-09-27 15:51 58阅读 0赞

项目结构:注意文件路径和文件位置!!!

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准备接口和mapper映射文件

EmpMapper接口

package com.msb.mapper;
    import com.msb.pojo.Emp;
    import java.util.List;
    /**
     * @Author: Ma HaiYang
     * @Description: MircoMessage:Mark_7001
     */
    public interface EmpMapper {
        /**
         * 该方法用于查询全部的员工信息
         * @return 全部员工信息封装的Emp对象的List集合
         */
        List<Emp> findAll();
    }

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EmpMapper.xml映射文件

<?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper
            PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
            "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.msb.mapper.EmpMapper">
        
        
        <select id="findAll" resultType="emp" >
            select * from emp
        </select>
    </mapper>

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在sqlMapConfig.xml核心配置文件中使用包扫描形式加载所有的映射文件

<mappers>
        
        <mapper class="com.msb.mapper.EmpMapper"/>
    </mappers>

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测试代码

package com.msb.test;
    import com.msb.mapper.EmpMapper;
    import com.msb.pojo.Dept;
    import com.msb.pojo.Emp;
    import org.apache.ibatis.io.Resources;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.apache.ibatis.session.SqlSessionFactoryBuilder;
    import org.junit.After;
    import org.junit.Before;
    import org.junit.Test;
    import java.io.IOException;
    import java.io.InputStream;
    import java.util.List;
    /**
     * @Author: Ma HaiYang
     * @Description: MircoMessage:Mark_7001
     */
    public class Test1 {
        private SqlSession sqlSession;
        @Before
        public void init(){
            SqlSessionFactoryBuilder ssfb =new SqlSessionFactoryBuilder();
            InputStream resourceAsStream = null;
            try {
                resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");
            } catch (IOException e) {
                e.printStackTrace();
            }
            SqlSessionFactory factory=ssfb.build(resourceAsStream) ;
            sqlSession=factory.openSession();
        }
        @Test
        public void testFindAll(){
            EmpMapper empMapper=sqlSession.getMapper(EmpMapper.class);
            List<Emp> emps = empMapper.findAll();
            emps.forEach(System.out::println);
        }
        @After
        public void release(){
            // 关闭SQLSession
            sqlSession.close();
        }
    }

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代理模式浅析

mybatis是如何通过代理模式实现查询的

这条语句的底层使用了动态代理模式，动态创建一个EmployeeMapper的一个代理对象并赋给接口引用。所以在MyBatis中不需要显式提供Mapper接口的实现类，这也是简单的地方。

[0e674ecaaa30a30f5bcb21de79526ffd.png]: https://img-blog.csdnimg.cn/img_convert/0e674ecaaa30a30f5bcb21de79526ffd.png
[6c0fa22a99d7f481f7695b34e9457e96.gif]: https://img-blog.csdnimg.cn/img_convert/6c0fa22a99d7f481f7695b34e9457e96.gif
[aa667803de871ffacd8c4610ec70a596.gif]: https://img-blog.csdnimg.cn/img_convert/aa667803de871ffacd8c4610ec70a596.gif
[90a54d5929b56aa5ccf24b23d50b7fc3.gif]: https://img-blog.csdnimg.cn/img_convert/90a54d5929b56aa5ccf24b23d50b7fc3.gif
[824f01c3d6a3a8a0079715b0e90a7f85.gif]: https://img-blog.csdnimg.cn/img_convert/824f01c3d6a3a8a0079715b0e90a7f85.gif
[Image 1]: 
[192d5dbc0c02741ade8e0eb84048a91f.gif]: https://img-blog.csdnimg.cn/img_convert/192d5dbc0c02741ade8e0eb84048a91f.gif
[fc75a189ee003a5be224c96a77a42064.gif]: https://img-blog.csdnimg.cn/img_convert/fc75a189ee003a5be224c96a77a42064.gif
[be7a02d8b9063d5642c6ffe9c7c0ee27.gif]: https://img-blog.csdnimg.cn/img_convert/be7a02d8b9063d5642c6ffe9c7c0ee27.gif