MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

1.导入依赖

<dependencies>
        <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.21</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
        </dependency>
    </dependencies>

    <!--<properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>-->

    <!--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/resources</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>

2.核心配置文件

(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">
<!--核心配置文件-->
<configuration>
    <!--优先使用外部文件的-->
    <properties resource="db.properties">
        <!--<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=GMT%2B8"/>
        <property name="username" value="root"/>
        <property name="password" value="123456"/>-->
    </properties>

    <typeAliases>
        <!--方式一-->
        <!--<typeAlias type="com.jiutian.pojo.User" alias="User"/>-->
        <!-- 方式二，默认别名则为实体类名，首字母可小写-->
        <package name="com.jiutian.pojo"/>
    </typeAliases>
    <!--设置环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>

        <environment id="test">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTimezone=GMT%2B8"/>
                <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>
        <!--方式一-->
        <!--<mapper resource="com/jiutian/dao/UserMapper.xml"/>-->
        <!--方式二，要求接口和其Mapper配置文件同名且在同一个包下-->
        <!--<mapper class="com.jiutian.dao.UserMapper"/>-->
        <!--方式三，要求接口和其Mapper配置文件同名且在同一个包下-->
        <package name="com.jiutian.dao"/>
    </mappers>
</configuration>

3.Mapper配置文件

<?xml version="1.0" encoding="UTF8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<!--命名空间：绑定一个指定的Dao/Mapper接口-->
<mapper namespace="com.jiutian.dao.UserMapper">
    <select id="getUserList" resultType="User">
        select * from mybatis.user
    </select>

    <insert id="addUser" parameterType="User">
        insert into mybatis.user (id,name,pwd) values (#{id},#{name},#{pwd});
    </insert>

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

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

4.工具类

//SqlSessionFactoryBuilder-->SqlSessionFactory-->SqlSession
public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory;
    static {
        String resource = "mybatis-config.xml";
        try {
            //获取sqlSessionFactory对象
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

5.测试

如果是增删改操作，需要提交事务

public class UserDaoTest {
    @Test
    public void getUserList() {
        //获得SqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try {
            //方式一  :getMapper（推荐）
            UserMapper userDao = sqlSession.getMapper(UserMapper.class);
            List<User> userList = userDao.getUserList();
            //方式二
            //List<User> userList = sqlSession.selectList("com.jiutian.dao.UserMapper.getUserList");
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            //关闭SqlSession
            sqlSession.close();
        }
    }
}