Mybatis_第一节：第一个Mybatis程序

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mybatis – MyBatis 3 | 简介

一、第一个Mybatis程序

1、搭建环境

1）创建数据库

• 创建mybatis数据库
• 创建user表（int id,varchar name,varchar pwd）
• 插入数据

2）新建项目

• 创建一个普通maven工程

• 删除src目录

• 导入maven依赖<pom.xml>

<!--    导入依赖-->
    <dependencies>
<!--        mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.25</version>
        </dependency>
<!--        mybatis-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>
<!--        junit-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.2</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

2、创建一个模块

1）创建新的Module

• resource下新建<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">
<!--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?serverTimezone=GMT&amp;useUnicode=true&amp;useSSL=true&amp;characterEncoding=UTF-8"/>
                <property name="username" value="ROOT"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="org/mybatis/example/BlogMapper.xml"/>
    </mappers>
</configuration>

• 连接数据库：
  点击开发工具右侧database >>mysql >>root/123456 >>url后面加：?serverTimezone=GMT （改时区）>>在Schemas中选择对应数据库 >>成功导入数据库

2）编写mybatis的工具类的

• 第一步：获取sqlSessionFactory对象<MybatisUtils.java>

• 第二步：从 SqlSessionFactory 中获取 SqlSession

package com.pf.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;

/**
 * @ description: SqlSessionFactory构建sqlSession
 * @ author: perfer.PF
 * @ time: 2022/1/14 - 23:47
 */
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。
//    SqlSession 提供了在数据库执行 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。
    /** 
    * @Description: 调用sqlSessionFactory对象
    * @Param: []
    * @return: SqlSession
    * @Author: perfer
    * @Date: 2022/1/15
    */
    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

}

之后使用数据库只需调用sqlSession实例

3、编写代码

1）实体类

package com.pf.pojo;

/**
 * @ description:实体类
 * @ author: perfer.PF
 * @ time: 2022/1/15 - 0:07
 */
public class User {
    private int id;
    private String name;
    private String pwd;

    public User(){

    }

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

2）Dao接口

• interface接口

package com.pf.dao;

import com.pf.pojo.User;

import java.util.List;

/**
 * @ description:
 * @ author: perfer.PF
 * @ time: 2022/1/15 - 0:09
 */
public interface UserDao {
    List<User> getUserList();
}

3）接口实现类

• 由原来的UserDaoImpl转化为Mapper.xml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.pf.dao.UserDao">
<!--    查询语句-->
    <select id="getUserList" resultType="com.pf.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

4、测试

1）注意点

• 配置文件没有注册

  ​ MapperRegistry是什么？ >> 核心配置文件中注册mappers

• 绑定接口错误

• 方法名不对

• 返回类型不对

• Maven导出资源

2）解决Maven资源过滤问题

• pom文件配置添加：

<build>
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>

3）junit测试

package com.pf.dao;

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

import java.util.List;

/**
 * @ description:
 * @ author: perfer.PF
 * @ time: 2022/1/15 - 0:26
 */
public class UserDaoTest {

    @Test
    public void test(){
        //获取sqlSession对象
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        //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();
    }
}

n = MybatisUtils.getSqlSession();
//执行SQL
UserDao userDao = sqlSession.getMapper(UserDao.class);
List userList = userDao.getUserList();

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

    //关闭sqlSession
    sqlSession.close();
}

}

👆👆👆以上就可以简单实现一个mybatis