Mybatis配置

 （首先，在数据库中创建一张表，用于测试Mybatis连接）

use draft;/*这是我自己的数据库*/

create table if not exists emp(
    id int primary key auto_increment comment '编号',
    name varchar(10) comment '姓名',
    age int unsigned comment '年龄'
)comment '员工表' charset = utf8;

insert into emp (id,name, age) values (1,'Mike',21),
                                      (2,'Joe',23),
                                      (3,'John',20),
                                      (4,'Eder',20),
                                      (5,'Musk',26);

1、创建maven项目

2、 导入mybatis以及需要用的依赖 

官网 https://mvnrepository.com 下载maven的各种依赖

    <!--Maven 依赖--> <!--官网 https://mvnrepository.com 下载maven所有依赖版本-->
    <dependencies>

        <!--Junit依赖-->
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.13.2</version>
            <scope>test</scope>
        </dependency>

        <!--Mysql依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.31</version>
        </dependency>

        <!--Mybatis依赖-->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.11</version>
        </dependency>

        <!--lombok依赖--><!--可以快速创建User实体类-->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.30</version>
            <scope>provided</scope>
        </dependency>

    </dependencies>

3、创建实体类"User"，成员属性最好和数据库各字段对应

package com.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Integer id;
    private String name;
    private Integer age;
}

4、创建mapper接口"UserMapper"

package com.mapper;

import com.pojo.User;

import java.util.List;

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

5、创建mybatis配置文件"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>

    <!--<settings>
        <setting name="logImpl" value="STDOUT_LOGGING"/>&lt;!&ndash;STDOUT_LOGGING 是 Mybatis自带的日志&ndash;&gt;
    </settings>-->
    <typeAliases>
        <!--<package name="com.pojo"/>--><!--默认别名是实体类名，首字母小写-->
        <typeAlias alias="user" type="com.pojo.User"/><!--起别名的两种方式都行--><!--第一种是扫描某个包，第二种是给某一个实体类起别名-->
    </typeAliases>

    <environments default="development"><!--默认使用 id="development" 的环境配置-->
        <environment id="development"><!--可以配置多个 environment -->
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED"><!--Mybatis自带的数据库连接池POOLED--><!--也可以用其他的，不过要加maven依赖-->
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/><!--数据库信息，和JDBC一样的-->
                <property name="url" value="jdbc:mysql://localhost:3306/draft"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
            </dataSource>
        </environment>
    </environments>
    <mappers><!--加载映射文件-->
        <mapper resource="mapper/UserMapper.xml"/><!--加载单个文件--><!--可以等UserMapper.xml创建好了再写路径-->
        <!--<package name="mapper"/>&lt;!&ndash;扫描mapper包下的所有映射文件&ndash;&gt;-->
    </mappers>
</configuration>

6、创建 mapper接口的配置文件"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 namespace="com.mapper.UserMapper"><!--映射到UserMapper接口-->

    <select id="getUsers" resultType="user"><!--id就是接口里的抽象方法，resultType 返回值类型-->
        select * from emp
    </select>


</mapper>

7、建一个工具类"MyUtil"，用于获取sqlsession对象

 

package com.util;

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;

//用于获取一个SqlSession对象
public class MyUtil {
    private static final SqlSessionFactory sqlSessionFactory;

    static {
        String resource = "mybatis-config.xml";
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream(resource);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

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

8、测试 

import com.mapper.UserMapper;
import com.pojo.User;
import com.util.MyUtil;
import org.apache.ibatis.session.SqlSession;

import java.util.List;

public class MyTest {
    public static void main(String[] args) {
        SqlSession sqlSession = new MyUtil().getSqlSession();
        UserMapper mapper = sqlSession.getMapper(UserMapper.class);
        List<User> users = mapper.getUsers();
        users.forEach(System.out::println);
        sqlSession.close();//记得关闭资源
    }
}

 

最后，这是我的项目结构 

Mybatis入门官网 https://mybatis.net.cn