Mybatis简单入门（Idea+maven）（简要）

在项目开始之前需要在Mysql中创建需要的数据库和表，并且插入数据。
最终maven项目目录如下：

1.首先创建一个maven项目，并且配置Mysql链接：

2.在pom.xml中导入相关依赖

    <dependencies>

    <!--mysql驱动-->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.47</version>
    </dependency>
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.2</version>
    </dependency>

    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.12</version>
    </dependency>

</dependencies>

3.创建并编写工具类

package com.kuang.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 MybatisUtils {

    private static SqlSessionFactory sqlSessionFactory;


    static {
        //使用mybatis 获取sqlsessionfactory对象
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);

          ///  SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);


        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    //从sqlsessionfactory中获取sqlsession的实例
    //sqlsession完全包含了面向数据库执行sql命令所需要的所有方法
    public static SqlSession getSqlSession(){

            return sqlSessionFactory.openSession();
        }
}

4.编写配置文件，在resources目录下创建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>
    <!--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/mybatis01?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="com/kuang/dao/UserMapper.xml"/>
    </mappers>
</configuration>

5.创建一个实体类，并且加入getter，setter，toString方法

6.创建一个接口

package com.kuang.dao;
import com.kuang.pojo.User;

import java.util.List;

public interface UserDao {
     List<User> getUserList();


}

7.mapper配置文件（接口实现类）

<?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">

<!--命名空间  绑定一个对应的dao接口 -->
<mapper namespace="com.kuang.dao.UserDao">

       <select id="getUserList" resultType="com.kuang.pojo.User">
--            执行sql
           SELECT  * FROM  mybatis01.user;

       </select>
</mapper>

8.创建测试类，进行测试

package com.kuang.dao;

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

import java.util.List;

public class UserDaoTest {

    @Test
    public  void  test(){
        //  获得sqlsession对象
       SqlSession sqlSession= MybatisUtils.getSqlSession();
        // 方式一：执行sql
       UserDao userDao= sqlSession.getMapper(UserDao.class);
      List<User> userList= userDao.getUserList();
      for (User user:userList){

          System.out.println(user);

      }
      //关闭sqlsession

     sqlSession.close();

    }


}

注意：如果出现空指针异常可以参考下文:
https://blog.youkuaiyun.com/qq_43133294/article/details/108072863