Mybatis【第一个Mybatis程序】

二、第一个Mybatis程序

思路：搭建环境-->导入Mybatis-->编写代码-->测试

2.1搭建环境

搭建数据库

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;

select * from user;

insert into `user` (`id`,`name`,`pwd`) VALUES
(1,'酱油','123456'),
(2,'张三','123456'),
(3,'李四','123456')

新建项目

1.新建一个普通的maven项目

2.删除src目录

3.导入maven依赖

<?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>com.jiang</groupId>
    <artifactId>Mybatis-Study</artifactId>
    <version>1.0-SNAPSHOT</version>


    <!--导入依赖-->
    <dependencies>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <!--mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.2</version>
        </dependency>
        <!--junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>


    </dependencies>

</project>

2.2创建一个模块

编写mybatis的核心配置文件

<?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核心配置文件-->
<configuration>
    <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/mybatis?useSSL=true&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

编写mybatis工具类

package com.jiang.util;

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;

//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 = null;
            inputStream = Resources.getResourceAsStream(resource);
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    //既然有了SqlSessionFactory，顾名思义，我们就可以从中获得SqlSession的实例了
    //SqlSession完全包含了面向数据库执行SQL命令所需的所有方法
    public static SqlSession getSqlSesssion(){
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return  sqlSession;
    }



}

2.3、编写代码

实体类

package com.jiang.pojo;

import lombok.Data;
import lombok.RequiredArgsConstructor;

@Data
@RequiredArgsConstructor
public class user {
    private int id;
    private String name;
    private String pwd;
}

Dao接口

package com.jiang.dao;

import com.jiang.pojo.User;

import java.util.List;

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

}

接口实现类由原来的UserDaoImpl转变为一个Mapper配置文件

<?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.jiang.dao.UserDao">
    <!--id为dao/mapper层内函数的名字，resultType返回结果-->
   <select id="getUserList" resultType="com.jiang.pojo.User">
       select * from mybatis.user;
   </select>
</mapper>

2.4、测试

MapperRegistry是什么？

核心配置文件中注册mappers

  <!--每一个Mapper.XML都需要在Mybatis核心配置文件中注册-->
    <mappers>
        <mapper resource="com/jiang/dao/UserMapper.xml"></mapper>
    </mappers>

Junit测试

package com.jiang.dao;

import com.jiang.pojo.User;
import com.jiang.util.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 sqlSesssion = MybatisUtils.getSqlSesssion();
        //执行SQL
        //方式一：getMapper
        UserDao userDao = sqlSesssion.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();

        //方式二：
        List<User> userList =     sqlSesssion.selectList("com.jiang.dao.UserDao.getUserList");


        for (User user:userList) {
            System.out.println(user);
        }

        //关闭SqlSession
        sqlSesssion.close();
    }
}

可能会遇到的问题

1.配置文件没有注册

2.绑定接口错误

3.方法名不对

4.返回类型不对

5.Maven导出资源问题

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https://www.bilibili.com/video/BV1NE411Q7Nx?p=3&spm_id_from=pageDriver