首先，附上MyBatis3官方文档链接：当当当当！！！
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MyBatis3

创建一个普通的maven工程

项目结构如下图：父工程mybatis-study—>子工程mybatis-01
父工程pom.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.example</groupId>
    <artifactId>mybatis-study</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis-01</module>
    </modules>
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.4</version>
        </dependency>
    </dependencies>
<!--    在资源中配置resources，防止资源导出失败-->
    <build>
        <resources>
            <resource>
                <directory>src/main/rescources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
</project>

子工程pom.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <artifactId>mybatis-study</artifactId>
        <groupId>org.example</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>
    <artifactId>mybatis-01</artifactId>
    <!--    在资源中配置resources，防止资源导出失败-->
    <build>
        <resources>
            <resource>
                <directory>src/main/rescources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>
    <dependencies>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <version>42.1.1</version>
        </dependency>
    </dependencies>
</project>

项目中各个包中的接口、类与配置文件

utils工具类包

Mybatis框架获取sqlSession对象的工具类，这一部分是固定的，把他封装成工具类，便与调用；

/**
 * @author ：shijinliang
 * @date ：2021/8/16 10:00
 * @description：
 */
public class MyBatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            //使用mybatis第一步，获取sqlsessionfactory对象
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    //有了sqlsessionfactory对象，就可以获取SqlSession实例
    //SqlSession完全包含面向数据库执行SQL所需的方法
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }
}

pojo包

User实体类
映射数据库表中的字段

/**
 * @author ：shijinliang
 * @date ：2021/8/17 13:48
 * @description：
 */
public class User {
    private int id;
    private String name;
    private String pwd;

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

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

    public void setName(String name) {
        this.name = name;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public String getPwd() {
        return pwd;
    }

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

    public User() {
    }
}

dao包

UserMapper接口
定义增删改查的抽象方法接口

/**
 * @author ：shijinliang
 * @date ：2021/8/17 14:01
 * @description：
 */
public interface UserMapper {
    //查询全部用户
    List<User> getUserList();

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

    //insert插入数据
    int addUser(User user);

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


    //删除用户
    int deleteUser(int id);

}

dao接口的实现类改为配置文件UserMapper.xml
SQL语句在这里编写，之后更改功能只需更改配置文件即可增加新的数据库操作；

<?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.hikvision.shijinliang.dao.UserMapper">
    <!--  id=“ ” 绑定方法  -->
    <!--  resultType为返回值类型  -->
    <select id="getUserList" resultType="com.hikvision.shijinliang.pojo.User">
        select * from "user"
    </select>

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

    <!-- 实体类中的属性可以直接取出来放在#{}中   -->
    <insert id="addUser" parameterType="com.hikvision.shijinliang.pojo.User">
        insert into "user" ( id, name, pwd ) values (#{id},#{name},#{pwd})
    </insert>

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

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

resources 资源包

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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="org.postgresql.Driver"/>
                <property name="url" value="jdbc:postgresql://127.0.0.1:5432/postgres"/>
                <property name="username" value="postgres"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/hikvision/shijinliang/dao/UserMapper.xml"/>
    </mappers>
</configuration>

CRUD参数介绍

在这里插入图片描述

namespace
namesplace中的包名要和mapper接口包名一致！
select查询语句：
id：namespace中的方法名;
resultType：SQL语句执行的返回值;
paraterType：crud方法的参数类型，是实体类的话就是实体类的全类名com.hikvision.shijinliang.User;

原文链接：https://blog.csdn.net/weixin_42880265/article/details/119757508