20220628_MyBatis首次使用案例

@[toc]首先创建一个供查询的数据库和表

create database mybatis;
use mybatis;
drop table if exists mybatis;

create table tb_users(
    id int primary key auto_increment,
    username varchar(20),
    password varchar(20),
    gender char(1),
    address varchar(30)
);

insert into tb_users values (1,'马大帅', '1234','M','莲花乡马家堡子');
insert into tb_users values (2,'范德彪', '5678','M','开原维多利亚玉乐广场');
insert into tb_users values (3,'罗翔', '9876','M','厚大法考');
select *
from tb_users;
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结果如图

新建一个名为mybatis_demo的maven模块
给pom.xml文件添加依赖

    <dependencies>
        <dependency>
            <!--mybatis的依赖-->
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.10</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.29</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.20</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>1.2.11</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
            <version>1.2.11</version>
        </dependency>
    </dependencies>
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在main\resources文件夹里新建一个logback.xml文件，内容如下

<?xml version="1.0" encoding="UTF-8" ?>
<configuration>
    <!--
        CONSOLE ：表示当前的日志信息是可以输出到控制台的。
    -->
    <appender name="Console" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>【%level】 %blue(%d{HH:mm:ss.SSS}) %cyan(【%thread】) %boldGreen(%logger{15}) - %msg %n</pattern>
        </encoder>
    </appender>

    <logger name="com.diy" level="DEBUG" additivity="false">
        <appender-ref ref="Console"/>
    </logger>

    <root level="DEBUG">
        <appender-ref ref="Console"/>
    </root>
</configuration>
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同样的方法建一个mybatis的核心配置文件，内容在官网拷贝，修改数据库连接信息为本地信息即可

<?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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <!--数据库链接信息-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql:///mybatis?useSSl=false"/>
                <property name="username" value="root"/>
                <property name="password" value="1234"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
    	<!--此处加载sql的映射文件-->
        <mapper resource="tb_usersMapper.xml"/>
    </mappers>
</configuration>
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mappers标签下是sql语句的映射文件，配置sql映射文件后将路径复制进去
创建本例要用的user类，在main\java路径下

package com.diy.pojo;

public class User {
    private int id;
    private String username;
    private String password;
    private char gender;
    private String address;

    public User() {
    }

    public User(int id, String username, String password, char gender, String address) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.gender = gender;
        this.address = address;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public char getGender() {
        return gender;
    }

    public void setGender(char gender) {
        this.gender = gender;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", gender=" + gender +
                ", address='" + address + '\'' +
                '}';
    }
}
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创建sql映射文件，示例也在mybatsi官网有，修改命名空间，随意
修改标签id，结果类型改成刚才创建的类的全名

<?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 namespace="mybatis.TestMapper">
    <select id="queryAll" resultType="com.diy.pojo.User">
        select * from tb_users
    </select>
</mapper>
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因为本xml和核心配置文件在一个路径下，平级，所以将本文件名复制到核心配置文件的mappers标签里即可

最后写执行程序main方法，在main\java路径下
第一步的三行代码在官网复制后修改

package com.diy.mybatis;

import com.gable.pojo.User;
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;
import java.util.List;

public class Demo {
    public static void main(String[] args) throws IOException {
        //1.加载mybatis核心配置文件，获取SqlSessionFactory对象
        String resource = "mybatis-config.xml";//在resources根目录下，直接写名字就可以
        InputStream inputStream = Resources.getResourceAsStream(resource);
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        //2.用获取到的工厂来获取SqlSession对象，就能执行sql语句了
        SqlSession sqlsess = sqlSessionFactory.openSession();

        //3.执行sql
        List<User> users = sqlsess.selectList("mybatis.TestMapper.queryAll");

        System.out.println(users);

        //4.释放资源，关掉session即可
        sqlsess.close();
    }
}
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执行效果如下
我的idea控制台输出中文有乱码，无法完美解决

总结本例思路
1.创建maven项目，或者模块mybatis，maven的pom.xml配置文件例导入相关依赖，尤其是mybatis的依赖

2.编写配置文件，日志logback的，mybatis的核心配置文件

3.编写执行程序要用到的sql语句映射文件Mapper.xml

4.创建返回结果类

5.写主程序，思路见代码

6.报错根据提示修改相关依赖的版本