1. namespace
namespace中的包名要和接口的包名一致
2.select
选择/查询语句
id:就是对应的namespace中的方法名
resultType：Sql语句执行的返回值！
paramteType：参数类型！
列子：
1.编写接口

//查询全部用户
    List<User> getUserList();

2.编写对应的sql中的语句

<!--查询语句-->
    <select id="getUserList" resultType="com.yz.pojo.User">
        select *from mybatis.user;
    </select>

3.测试

   @Test
    public  void getUserById(){
        SqlSession sqlSession=MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1);
        System.out.println(user);
        sqlSession.commit();
        sqlSession.close();
    }

    //增删改查需要提交事务

---

1.select

 <!--查询语句-->
    <select id="getUserList" resultType="com.yz.pojo.User">
        select *from mybatis.user;
    </select>
    <select id="getUserById" parameterType="int" resultType="com.yz.pojo.User">
        select *from mybatis.user where id=#{id}

2.insert（插入）

 <!--对象中的属性可以直接取出来-->
    <insert id="addUser" parameterType="com.yz.pojo.User">
    insert  into mybatis.user(id, name, pwd) values (#{id},#{name },#{pwd})
</insert>

3.update（修改）

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

4.delete（删除）

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

完整步骤：
导入依赖：
父依赖：pom.xml

<?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>
    <!--父工程-->
    <groupId>com.yz</groupId>
    <artifactId>mybatis-study</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>mybatis-01</module>
    </modules>
    <dependencies>
        <!--导入依赖-->
        <dependency>
            <!--mysql驱动-->
            <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>3.5.9</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>
    <!--    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>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
            </resource>
        </resources>
    </build>

创建数据库：

create database  `mybatis`;
USE `mybatis`;
CREATE TABLE `user`(
`id` INT(20) NOT null primary key,
`name` varchar(30) default NULL,
`pwd` varchar(30) default NUll
)engine=InnoDB default CHARSET=utf8;
insert INTO `user`(`id`,`name`,`pwd`) values 
(1,'狂神','123456'),
(2,'张三','123456'),
(3,'李四','123456')

Uer.java（实体类）

package com.yz.pojo;

public class User {
    private int id;
    private String name;
    private  String pwd;

    public User(String s, String 哈哈, String pwd) {
    }

    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 + '\'' +
                '}';
    }
}

MybatisUtils.java (工具类）

package com.yz.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;
//构建 SqlSessionFactory-->sqlSession
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();
        }
    }
    //    既然有了 SqlSessionFactory，顾名思义，我们可以从中获得 SqlSession 的实例。
//    org.apache.ibatis.session.SqlSession 提供了在数据库执行 org.apache.ibatis.jdbc.SQL 命令所需的所有方法。
// 你可以通过 SqlSession 实例来直接执行已映射的 SQL 语句。
    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

UserDao接口

package com.yz.dao;
        import com.yz.pojo.User;
        import java.util.List;
public interface UserMapper {
    //查询全部用户
    List<User> getUserList();
    //根据ID查询用户
    User getUserById(int id);
    //insert 一个用户（插入）
    int addUser(User user);
    //修改用户
    int upadteUser(User user);
    //删除用户
    int deleteUser(int id);
}

UserMapper.xml(SQL语句）

<?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.yz.dao.UserMapper">
    <!--查询语句-->
    <select id="getUserList" resultType="com.yz.pojo.User">
        select *from mybatis.user;
    </select>
    <select id="getUserById" parameterType="int" resultType="com.yz.pojo.User">
        select *from mybatis.user where id=#{id}
    </select>
    <!--对象中的属性可以直接取出来-->
    <insert id="addUser" parameterType="com.yz.pojo.User">
    insert  into mybatis.user(id, name, pwd) values (#{id},#{name },#{pwd})
</insert>
    <update id="upadteUser" parameterType="com.yz.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>

测试：UerDao.java

package com.yz.dao;
import com.yz.pojo.User;
import com.yz.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class UserDaoTest {
    @Test
    public void test() {
        //第一步:获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        try {
            //方式一:getMapper
            UserMapper userdao = sqlSession.getMapper(UserMapper.class);
            List<User> userList = userdao.getUserList();
            //方式二:
//        List<User> userList=sqlSession.selectList("com.yz.dao.UserDao.getUserList");
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {

        } finally {
//关闭sqlSession
            sqlSession.close();
        }
    }
    @Test
    public  void getUserById(){
        SqlSession sqlSession=MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        User user = mapper.getUserById(1);
        System.out.println(user);
        sqlSession.close();
    }
    //增删改查需要提交事务
@Test
    public void addUser(){
        SqlSession sqlSession=MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    int result = mapper.addUser(new User(7,"tt","12345"));
    if (result>0){
        System.out.println("插入成功！");
    }
    //提交事务
    sqlSession.commit();
    sqlSession.close();
    }
    @Test
    public  void updateUser(){
        SqlSession sqlSession=MybatisUtils.getSqlSession();
        UserMapper mapper=sqlSession.getMapper(UserMapper.class);
        mapper.upadteUser(new User(4,"呵呵呵","1234456"));
        sqlSession.commit();
        sqlSession.close();
    }
    @Test
    public void deleteUser(){
        SqlSession sqlSession=MybatisUtils.getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        mapper.deleteUser(0);
        sqlSession.commit();
        sqlSession.close();
    }
}

注意：
增删改查需要提交事务
sqlSession.commit();