Note: the development environment used is IDEA

1. import dependency
   enter relevant dependency information in pom.xml

<!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.47</version>
        </dependency>
        <!--mybatis-->
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>

        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>

<!--核心配置文件-->
<configuration>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>

    <!--每一个Mapper.xml都需要在Mybatis核心配置文件中注册！-->
    <mappers>
        <mapper resource="com/liu/mapper/UserMapper.xml"/>
    </mappers>

</configuration>

MyBatis tool class
MybatisUtils

package com.liu.utils;

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;

/**
 * @author liucong
 * @date 2020/9/8 - 15:08
 */
//sqlSessionFactory --> sqlSession
public class MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;

    static{
        try {
            //使用Mybatis 第一步：获取sqlSessionFactory
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
    // SqlSession 提供了在数据库执行 SQL 命令所需的所有方法。
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

1. create entity class

package com.liu.pojo;

/**
 * @author liucong
 * @date 2020/9/8 - 15:24
 */
//实体类
public class User {
    private int id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(int id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    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;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

1. write Mapper interface class

package com.liu.mapper;

import com.liu.pojo.User;

import java.util.List;

/**
 * @author liucong
 * @date 2020/9/8 - 15:31
 */
public interface UserMapper {
    //查询全部用户
    List<User> getUserList();

    //根据ID查询用户
    User getUserById(int id);

    //增加一个用户
    int addUser(User user);

    //修改用户
    int updateUser(User user);

    //删除一个用户
    int deleteUser(int id);
}

1. write mapper. XML configuration file

<?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:绑定一个对应的Dao/Mapper接口-->
<mapper namespace="com.liu.mapper.UserMapper">
    <select id="getUserList" resultType="com.liu.pojo.User">
        select * from user
    </select>

    <select id="getUserById" parameterType="int" resultType="com.liu.pojo.User">
        select * from mybatis.user where id=#{id}
    </select>

    <insert id="addUser" parameterType="com.liu.pojo.User">
        insert into mybatis.user (id, name, pwd) VALUES (#{id},#{name},#{pwd})
    </insert>

    <update id="updateUser" parameterType="com.liu.pojo.User">
        update mybatis.user set name = #{name},pwd=#{pwd} where id=#{id};
    </update>

    <delete id="deleteUser" parameterType="int">
        delete from mybatis.user where id=#{id}
    </delete>

</mapper>

1. write test class

package com.liu.mapper;

import com.liu.pojo.User;
import com.liu.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

/**
 * @author liucong
 * @date 2020/9/8 - 15:54
 */
//org.apache.ibatis.binding.BindingException: Type interface com.liu.mapper.UserMapper is not known to the MapperRegistry.
//java.lang.ExceptionInInitializerError
public class UserMapperTest {
    @Test
    public void test(){
        //第一步：获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行SQL
        //方式一：getMapper
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> userList = mapper.getUserList();

        //方式二：
//        List<User> userList = sqlSession.selectList("com.liu.mapper.UserMapper.getUserList");

        for(User user:userList){
            System.out.println(user);
        }

        //关闭SqlSession
        sqlSession.close();
    }

    @Test
    public void test2(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1);
        System.out.println(user);

        sqlSession.close();
    }

    //增删改需要提交事务
    @Test
    public void test3(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        int res=mapper.addUser(new User(4,"王五","123456"));
        if(res>0){
            System.out.println("插入成功");
        }
        //提交事务
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void test4(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.updateUser(new User(4,"wangwu","1234"));
        sqlSession.commit();

        sqlSession.close();
    }

    public void test5(){
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(4);
        sqlSession.commit();
        sqlSession.close();
    }
}

possible problem note: Maven static resource filtering problem

adds

to the pom. XML file

<!--在build中配置resources,来防止我们资源导出失败的问题-->
    <build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>