1_使用Mapper代理方式实现查询

ゝ一纸荒年。 2023-09-30 20:13 3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。

[f04e14cac43f6f75fb0b56f3a150c822.png]: https://img-blog.csdnimg.cn/img_convert/f04e14cac43f6f75fb0b56f3a150c822.png
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[27c34d068bd929d157b29e583c99deb4.gif]: https://img-blog.csdnimg.cn/img_convert/27c34d068bd929d157b29e583c99deb4.gif
[e63e56a1b8f7a7a7194225b3ba1a4a4f.gif]: https://img-blog.csdnimg.cn/img_convert/e63e56a1b8f7a7a7194225b3ba1a4a4f.gif
[ffc6140d493d9a3b03e9c291642e6cfb.gif]: https://img-blog.csdnimg.cn/img_convert/ffc6140d493d9a3b03e9c291642e6cfb.gif
[4e2f749d9297eaf41ef65b66538f348d.gif]: https://img-blog.csdnimg.cn/img_convert/4e2f749d9297eaf41ef65b66538f348d.gif
[107d23085cd44ab1f085d384ec1494b2.gif]: https://img-blog.csdnimg.cn/img_convert/107d23085cd44ab1f085d384ec1494b2.gif
[ecc5acb6f17c43a8fc616ba82a45a15f.gif]: https://img-blog.csdnimg.cn/img_convert/ecc5acb6f17c43a8fc616ba82a45a15f.gif
[88e733223e6480480f5e73005fd4e838.gif]: https://img-blog.csdnimg.cn/img_convert/88e733223e6480480f5e73005fd4e838.gif