一.??初始化

首先创建一个maven的Module，然后执行下面步骤：

1. 在pom.xml中添加依赖

    <dependencies>
        <!-- Mybatis核心 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.8</version>
        </dependency>
        <!-- MySQL驱动 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.27</version>  <!-- 可以与自己电脑的mysql版本一致 -->
        </dependency>
    </dependencies>

2. 创建MyBatis核心配置文件

?在main目录下的resources目录下创建一个mybatis-config.xml文件

<?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>
    <!--设置连接数据库的环境-->
    <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/studymybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

3. 创建表

?在studymybatis数据库下创建一个user表

CREATE TABLE `studymybatis`.`user` (
  `id` INT NOT NULL AUTO_INCREMENT,
  `username` VARCHAR(20) NULL, UNIQUE,
  `password` VARCHAR(20) NULL,
  `age` INT NULL,
  `sex` CHAR(1) NULL,
  `email` VARCHAR(20) NULL,
  PRIMARY KEY (`id`),

4. 创建JavaBean对象

在main目录下的java目录下的pojo目录下创建一个User类

package pojo;

public class User {
    private Integer id;
    private String username;
    private String password;
    private Integer age;
    private Character sex;
    private String email;

    public User() {
    }

    public User(Integer id, String username, String password, Integer age, Character sex, String email) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.age = age;
        this.sex = sex;
        this.email = email;
    }

    public Integer getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Character getSex() {
        return sex;
    }

    public void setSex(Character sex) {
        this.sex = sex;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", age=" + age +
                ", sex=" + sex +
                ", email='" + email + '\'' +
                '}';
    }
}

5. 创建Mapper接口

在main目录下的java目录下的mapper目录下创建一个UserMapper接口（Mapper接口相当于DAO），在该接口中编写操作数据库的方法? ? ? ?

package mapper;

import pojo.User;

import java.util.List;

public interface UserMapper {

    int insertUser();   //添加用户信息

    void updateUser();  //修改用户信息

    void deleteUser();  //删除用户信息

    User queryUserByName();   //根据用户名查询用户信息

    List<User> queryAllUser();  //查询所有用户信息
}

6. 创建Mapper接口的映射文件

映射文件与mapper接口、接口中的方法对应，并在映射文件中编写sql语句。

注：一个表对应一个实体类对应一个mapper接口对应一个映射文件

①在resources目录下创建一个mapper目录（该目录名与存放mapper接口的包名一致，其用于存放每个接口所对应的映射文件）

②在resources目录下的mapper目录下创建一个映射文件：UserMapper.xml（该映射文件的名字与mapper接口同名）

③映射文件里的namespace要和mapper接口的全类名保持一致，这里为：mapper.UserMapper?

④映射文件里的SQL语句的id要和mapper接口中的方法名一致

⑤映射文件里查询功能的返回值类型是数据库表对应的JavaBean对象

<?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="mapper.UserMapper">

    <insert id="insertUser">
        insert into user values(null,'张三','1234',23,'男','zhang@163.com')
    </insert>

    <update id="updateUser">
        update user set age=22 where username='张三'
    </update>

    <delete id="deleteUser">
        delete from user where username='张三'
    </delete>

    <!-- 查询必须设置resultType或者resultMap，resultType：设置默认的映射关系，resultMap：设置自定义的映射关系-->
    <select id="queryUserByName" resultType="pojo.User">
        select * from user where username='张三'
    </select>

    <select id="queryAllUser" resultType="pojo.User">
        select * from user
    </select>

</mapper>

7. 在MyBatis核心配置文件引入映射文件

在mybatis-config.xml文件中添加以下内容

    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

即mybatis-config.xml文件变为：

<?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>
    
    <!--设置连接数据库的环境-->
    <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/studymybatis"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    
    <!--引入映射文件-->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>
</configuration>

8. 测试接口中的方法——操作数据库

import mapper.UserMapper;
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.Test;
import pojo.User;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

public class MybatisTest {
    @Test
    public void testInsert() throws IOException {
        //加载核心配置文件
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

        //获取SqlSessionFactoryBuilder
        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();

        //获取SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);

        //获取SqlSession（Java程序和数据库之间的会话），为true表示自动提交事务，默认为false
        SqlSession sqlSession = sqlSessionFactory.openSession(true);

        //获取Mapper接口对应的对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //操作数据库
        mapper.insertUser();
    }

    @Test
    public void testUpdate() throws IOException {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        SqlSession sqlSession = sqlSessionFactory.openSession(true);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        mapper.updateUser();
    }

    @Test
    public void testDelete() throws IOException {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        SqlSession sqlSession = sqlSessionFactory.openSession(true);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        mapper.deleteUser();
    }

    @Test
    public void testQueryByName() throws IOException {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        SqlSession sqlSession = sqlSessionFactory.openSession(true);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        User user = mapper.queryUserByName();

        System.out.println(user);
    }

    @Test
    public void testQueryAll() throws IOException {
        InputStream is = Resources.getResourceAsStream("mybatis-config.xml");

        SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
        SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
        SqlSession sqlSession = sqlSessionFactory.openSession(true);

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        List<User> list = mapper.queryAllUser();

        list.forEach(user -> System.out.println(user));
    }
}

二. 对上述配置进行优化

1. 优化核心配置文件

首先在resources目录下创建一个jdbc.properties文件

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/studymybatis
jdbc.username=root
jdbc.password=123456

然后将核心配置文件改为如下

<?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>

    <properties resource="jdbc.properties"/>

    <!--设置别名，以包为单位设置别名，这样不管该包下有多少个JavaBean，其别名都为其自身的类名-->
    <typeAliases>
        <package name="pojo"/>  <!-- name的值为实体对象类所在的包（全路径，只是这里只有一个目录pojo） -->
    </typeAliases>

    <!--设置连接数据库的环境-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <!--引入映射文件-->
    <!-- 由于mapper下可以有多个映射文件，且映射文件名与mapper接口名一致，可以直接写包名，一次引入所有映射文件 -->
    <mappers>
        <package name="mapper"/>
    </mappers>
</configuration>

将映射文件修改为

<?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="mapper.UserMapper">  <!--为mapper接口的全类名-->

    <insert id="insertUser">
        insert into user values(null,'张三','1234',23,'男','zhang@163.com')
    </insert>

    <update id="updateUser">
        update user set age=22 where username='张三'
    </update>

    <delete id="deleteUser">
        delete from user where username='张三'
    </delete>

    <!-- 查询必须设置resultType或者resultMap，resultType：设置默认的映射关系，resultMap：设置自定义的映射关系-->
    <!-- 由于在核心配置文件下设置了别名，这里resultType可以直接写成自身的类名-->
    <select id="queryUserByName" resultType="User">
        select * from user where username='张三'
    </select>

    <select id="queryAllUser" resultType="User">
        select * from user
    </select>

</mapper>

2. 编写工具类

由于操作数据库前都需要先获取SqlSession，所以可以将其编写成一个工具类SqlSessionUtils

package 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;

public class SqlSessionUtils {
    public static SqlSession getSqlSession(){
        SqlSession sqlSession = null;
        try {
            //加载核心配置文件
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            //获取SqlSessionFactoryBuilder
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //获取SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
            //获取SqlSession（Java程序和数据库之间的会话），为true表示自动提交事务，默认为false
            sqlSession = sqlSessionFactory.openSession(true);
        } catch (IOException e) {
            e.printStackTrace();
        }
        return sqlSession;
    }
}

import mapper.UserMapper;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import pojo.User;
import utils.SqlSessionUtils;
import java.util.List;

public class MybatisTest {
    @Test
    public void testInsert() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();

        //获取Mapper接口对应的对象
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //操作数据库
        mapper.insertUser();
    }

    @Test
    public void testUpdate() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        mapper.updateUser();
    }

    @Test
    public void testDelete() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        mapper.deleteUser();
    }

    @Test
    public void testQueryByName() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        User user = mapper.queryUserByName();

        System.out.println(user);
    }

    @Test
    public void testQueryAll() {
        SqlSession sqlSession = SqlSessionUtils.getSqlSession();

        UserMapper mapper = sqlSession.getMapper(UserMapper.class);

        //调用方法操作数据库
        List<User> list = mapper.queryAllUser();

        list.forEach(user -> System.out.println(user));
    }
}