准备

Java 18
mysql 8
maven
idea

mysql

准备数据

CREATE DATABASE `mybatis`;

USE `mybatis`;

CREATE TABLE `user`(
`id` int not null PRIMARY KEY,
`name` varchar(30) DEFAULT NULL,
`pwd` varchar(30) DEFAULT NULL
)ENGINE=INNODB,CHARSET=utf8;

INSERT INTO `mybatis`.`user` (`id`, `name`, `pwd`) 
VALUES 
(1, 'haha', '123'),
(2, 'lala', '123'),
(3, 'xixi', '1234');

开始

新建maven项目

这个就不用详细说了
新建maven项目，然后新建一个module作为第一个mybatis程序
整体文件目录如下
在这里插入图片描述

maven添加引用

在外面一层的pom添加引用
mysql-connect
mybatis
junit（用于测试代码）

<dependencies>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.33</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.13</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

mybatis配置文件

在resource文件夹下添加mybatis配置文件mybatis-config.xml
mappers页签中的内容可以先不写，等创建mapper后再添加

<?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=false&amp;useUnicode=true&amp;characterEncoding=UTF-8&amp;serverTime=Asia/shanghai"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="com/cpyy/mapper/UserMapper.xml"/>
    </mappers>
</configuration>

工具类

创建utils工具类，方便代码复用

package com.cpyy.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 {
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession(){
        return sqlSessionFactory.openSession();
    }

}

创建实例类

创建实体类，和mysql表中的信息保持一致
（未包含构造器等代码）

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

添加mapper

创建mapper后可以在mybatis-config.xml中补充相应内容

mapper

package com.cpyy.mapper;

import com.cpyy.pojo.User;

import java.util.List;

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

mapper.xml

mapper.xml中的namespace为上方mapper的路径

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.cpyy.mapper.UserMapper">
    <select id="getUserList" resultType="com.cpyy.pojo.User">
        select * from mybatis.user
    </select>
</mapper>

测试类

在test目录中创建测试类，可以直接进行测试

package com.cpyy.mapper;

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

import java.util.List;

public class UserMapperTest {

    @Test
    public void getUserListTest() {

        try (SqlSession sqlSession = MybatisUtils.getSqlSession()) {
            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserList();
            for (User user : userList) {
                System.out.println(user);
            }
        } catch (Exception e) {
            e.printStackTrace();

        }

    }
}

正常结果如下
在这里插入图片描述

发现问题

org.apache.ibatis.binding.BindingException: Type interface com.cpyy.mapper.UserMapper is not known to the MapperRegistry.

在这里插入图片描述
在mybatis-config.xml中没有记录mapper信息，补充即可

The error may exist in com/cpyy/mapper/UserMapper.xml

找不到文件
在target中没有对应的UserMapper.xml文件，没有进行导出

在pom文件中添加文件过滤的内容

    <build>
        <resources>
            <resource>
                <directory>src/main/resource</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>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>17</source>
                    <target>17</target>
                </configuration>
            </plugin>
        </plugins>
    </build>

参考

mybatis官方文档