Teach you step by step how to write a MyBatis entry program

1.Create file

Here I named it myself: Code_Book

and select the Maven project when building the system

2.Introduce related dependencies

pom.xml file

<?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>org.example</groupId>
    <artifactId>Code_Book</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    
    
    
    <dependencies>
        <!--引入Mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-parent</artifactId>
            <version>37</version>
        </dependency>
        
        <!--引入测试依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>

3.Create database

(1) Create a new database

(2) Create a new user table (remember the primary key to increase automatically)

(3) Enter data

4. Create database connection information configuration file

Create the db.properties file directly in the resources directory

mysql.driver = com.mysql.cj.jdbc.Driver
mysql.url = jdbc:mysql://localhost:3306/mybatis?serverTimezone=UTC&characterEncoding=utf8&useUnicode=true&useSSL=false
mysql.username = root
mysql.password = 123456

5. Create the core configuration file of Mybatis

Create the mybatis-config.xml file directly in the resources directory

<?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>
    <!--
        属性配置，一般用于配置数据库，resource用于引用数据库配置文件的位置，
        配置好后可以使用${属性名}的形式使用
    -->
    <properties resource="db.properties"/>
    <!--环境配置-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>
            </dataSource>
        </environment>
    </environments>
</configuration>

6. Create entity classes (POJO entities)

(1) First create a new software package named: com

(2) Create a package in com as Study_1

(3) Create a pojo package; in the package, create a new entity class named User.

package com.Study_1.pojo;

public class User {

    private int uid; //用户id
    private String uname; //用户姓名
    private int uage; //用户年龄


    //写出Getter方法和Setter方法

    public int getUid() {
        return uid;
    }

    public void setUid(int uid) {
        this.uid = uid;
    }

    public String getUname() {
        return uname;
    }

    public void setUname(String uname) {
        this.uname = uname;
    }

    public int getUage() {
        return uage;
    }

    public void setUage(int uage) {
        this.uage = uage;
    }
}

7. Create mapping files

(1) Create a mapper folder in the resources directory

(2) Create a mapping file in the mapper folder named: UserMapper.xml

<?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">
<!--mapper为映射的根节点-->
<mapper namespace="com.Study_1.pojo.User">
<!--id = 接口中的方法名
    parameterType为传入的参数类型
    resultType为返回实体类对象，使用包名、类名
-->

    <select id="findById" parameterType="int" resultType="com.Study_1.pojo.User">
        select * from users where uid = #{id}

    </select>
</mapper>

8. Modify the mybatis-config.xml file

That is, add mapping file path configuration

<mappers>
    <mapper resource="mapper/UserMapper.xml"/>
</mappers>

The complete mybatis-config.xml file is as follows:

<?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>
    <!--
        属性配置，一般用于配置数据库，resource用于引用数据库配置文件的位置，
        配置好后可以使用${属性名}的形式使用
    -->
    <properties resource="db.properties"/>
    <!--环境配置-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${mysql.driver}"/>
                <property name="url" value="${mysql.url}"/>
                <property name="username" value="${mysql.username}"/>
                <property name="password" value="${mysql.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--映射器-->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

</configuration>

9.Write test classes

Create a Test package in com.Study_1

Then create the UserTest class in the Test package

package com.Study_1.test;

import com.Study_1.pojo.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.*;
import org.junit.Test;

import java.io.IOException;
import java.io.Reader;
import java.sql.Connection;
import java.sql.SQLOutput;

public class UserTest {
    @Test
    public  void userFindByIdTest(){
        String resources = "mybatis-config.xml";
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(resources);
        } catch (IOException e) {
            e.printStackTrace();
        }
        SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
        SqlSession session = sqlMapper.openSession();
        User user = session.selectOne("findById",1);
        System.out.println(user.getUname());
        session.close();
    }
}