Mybatis

简介

中文文档:https://mybatis.org/mybatis-3/zh/index.html

什么是Mybatis?

持久化

持久层

为什么需要Mybatis?

帮助程序员方便地将数据存储到数据库中，可以简化传统的JDBC代码。

优点

如何获得Mybatis?

依赖

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.13</version>
</dependency>

源码

Github中Mybatis源码：https://www.githubs.cn/projects/8205602-mybatis-3

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第一个Mybatis程序

思路：搭建环境---->导入Mybatis---->编写代码---->测试！

环境搭建

数据库准备

CREATE DATABASE `mybatis`;

USE `mybatis`;

CREATE TABLE `user`(
    `id` INT NOT NULL PRIMARY KEY,
    `name` VARCHAR(20) DEFAULT NULL,
    `pwd` VARCHAR(30) DEFAULT NULL
)ENGINE = InnoDB DEFAULT CHARSET=utf8mb4;

INSERT INTO `user`(`id`, `name`, `pwd`)VALUES
(1, 'khan', '1234'),
(2, 'louis', '123'),
(3, 'Alex', '1234')

新建项目

1、创建一个maven项目，补充目录结构。

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导入mybatis

2、导入相关依赖

<dependencies>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.32</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
    <dependency>
        <groupId>org.mybatis</groupId>
        <artifactId>mybatis</artifactId>
        <version>3.5.13</version>
    </dependency>
</dependencies>

编写程序

3、配置核心配置文件，命名为mybatis-config.xml

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<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <environments default="development">
        <environment id="development">
            <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}"/>
                <property name="username" value="${root}"/>
                <property name="password" value="${zkpk}"/>
            </dataSource>
        </environment>
    </environments>
    <!--每一个mapper.xml都需要在Mybatis核心配置文件中注册-->
    <mappers>
        <mapper resource="com/louis/dao/UserMapper.xml"/>
    </mappers>
</configuration>

4、编写mybatis工具类

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package com.louis.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;

/**
 * @author XRY
 * @date 2023年05月24日10:16
 */
public class MybatisUtils {
    private  static SqlSessionFactory sqlSessionFactory;
    static{
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
    //有了SqlSessionFactory,我们就可以从中获得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();
    }
}

5、编写代码

package com.louis.pojo;

/**
 * @author XRY
 * @date 2023年05月24日10:28
 */
public class User {
    private Integer id;
    private String name;
    private String pwd;

    public User() {
    }

    public User(Integer id, String name, String pwd) {
        this.id = id;
        this.name = name;
        this.pwd = pwd;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer 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 + '\'' +
                '}';
    }
}

//dao接口
package com.louis.dao;

import com.louis.pojo.User;

import java.util.List;

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

//dao接口实现类由原来的UserDaoImpl转为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.louis.dao.UserDao">
<!--查询语句， id对应原来的方法名字-->
    <select id="getUserList" resultType="com.louis.pojo.User">
--id就相当于重写了原来的接口
        select * from mybatis.user;
    </select>
</mapper>

测试

6、测试

package com.louis.dao;

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

import java.util.List;

/**
 * @author XRY
 * @date 2023年05月24日19:00
 */
public class UserDaoTest {
    @Test
    public void test(){
        //获得sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //执行sql
        //方式一：getMapper
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> userList = userDao.getUserList();
        //        List<User> userList = sqlSession.selectList("com.louis.dao.UserDao.getUserList");
        for (User user : userList) {
            System.out.println(user);
        }
        //关闭sqlSession
        sqlSession.close();
    }
}

问题及解决方式

1、注意：在运行的时候如果出现UserMapper.xml找不到的情况，这是因为maven的过滤机制导致的，我们只需要在pom.xml文件中添加如下配置：

<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>