Mybatis使用配置（2mapper代理）

项目结构：

目的：解决硬编码问题，更友好的调用封装好sql语句的接口方法
例：原生方法selectList()执行sql，还需要硬编码test.selectAll
List users = sqlSession.selectList(“test.selectAll”);

设置mapper代理步骤

---

UserMapper.xml（相当于实现UserMapper接口）

<?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">
<!--
    namespace="com.niujl.mapper.UserMapper"：名称空间地址要与定义sql语句的接口UserMapper一致
    id="selectAll"：相当于实现UserMapper接口的方法
-->
<mapper namespace="com.niujl.mapper.UserMapper">
    <select id="selectAll" resultType="com.niujl.pojo.User">
        select *
        from tb_user;
    </select>

</mapper>

UserMapper.java（sql语句接口定义）

package com.niujl.mapper;

import com.niujl.pojo.User;

import java.util.List;

public interface UserMapper {


    List<User> selectAll();

}

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
<!--        这个配置使得UserMapper.xml的resultType可以直接写类名User-->
        <package name="com.niujl.pojo"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
<!--                链接信息-->
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSL=false"/>
                <property name="username" value="root"/>
                <property name="password" value="admin"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
<!--        加载sql的映射文件-->
<!--        <mapper resource="com/niujl/mapper/UserMapper.xml"/>-->
        <package name="com.niujl.mapper"/>
    </mappers>
</configuration>

MyBatisDemo2.java（具体操作）

package com.niujl;

import com.niujl.mapper.UserMapper;
import com.niujl.pojo.User;
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 java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MyBatisDemo2 {
    public static void main(String[] args) throws IOException {
        //1、加载核心配置文件
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
//        2、获取SqlSession对象，用它来执行sql
        SqlSession sqlSession = sqlSessionFactory.openSession();
//        3、执行sql
//        List<User> users = sqlSession.selectList("test.selectAll");
//        System.out.println(users);
//        3、1获取UserMapper接口代理的对象
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = userMapper.selectAll();
        System.out.println(users);
//        4、释放资源
        sqlSession.close();
    }
}