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1.大致项目结构：

2.注意resources下mapper是新建文件夹形式

Pom.xml: 添加需要引入的依赖：

<?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>mybatis_dynamicSQL2</artifactId>
    <version>1.0-SNAPSHOT</version>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>8</source>
                    <target>8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
    <dependencies>

        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.7</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.16</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>RELEASE</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

</project>

Jdbc.properties:

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/ssm?useUnicode=true&characterEncoding=utf-8&useSSL=false&serverTimezone=GMT
jdbc.username=root
jdbc.password=123456

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>
    <!--引入配置文件-->
    <properties resource="jdbc.properties"/>
    <settings>
        <!--配置是否开启驼峰命名自动映射，即从经典数据库列名 A_COLUMN 映射到经典 Java 属性名 aColumn。默认为false-->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
    <typeAliases>
        <!--设置类型别名  这里是以包的形式，默认为类名-->
        <package name="com.mybatis.study.pojo"/>
    </typeAliases>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <!--将包内的映射器接口实现全部注册为映射器-->
        <package name="com.mybatis.study.mapper"/>
    </mappers>
    <!--https://mybatis.net.cn/configuration.html 可以去里面查-->
</configuration>

员工类Emp:

package com.mybatis.study.pojo;

public class Emp {
    private Integer id;
    private String empName;
    private Integer age;
    private String sex;

    public Emp() {
    }

    public Emp(Integer id, String empName, Integer age, String sex) {
        this.id = id;
        this.empName = empName;
        this.age = age;
        this.sex = sex;
    }

    public Integer getId() {
        return id;
    }

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

    public String getEmpName() {
        return empName;
    }

    public void setEmpName(String empName) {
        this.empName = empName;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Emp{" +
                "id=" + id +
                ", empName='" + empName + '\'' +
                ", age=" + age +
                ", sex='" + sex + '\'' +
                '}';
    }
}

Mapper:

EmpMapper:

package com.mybatis.study.mapper;

import com.mybatis.study.pojo.Emp;

import java.util.List;

public interface EmpMapper {
    /**
     * 获取所有员工
     * @return
     */
    List<Emp> selectAllEmp();
}

EmpMapper.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.mybatis.study.mapper.EmpMapper">
    <select id="selectAllEmp" resultType="emp">
        select * from t_emp
    </select>
</mapper>

工具类：utils:

SqlSession:

package com.mybatis.study.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 SqlSessionUtil {
    public static SqlSession getSqlSession(){
        SqlSession sqlSession =null;
        try {
            //获取核心配置文件的输入流
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            //获取SqlSessionFactoryBuilder
            SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
            //获取SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = sqlSessionFactoryBuilder.build(is);
            //获取SqlSession对象
            sqlSession = sqlSessionFactory.openSession(true);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return sqlSession;
    }
}

Test类：

package TestAll;

import com.mybatis.study.mapper.EmpMapper;
import com.mybatis.study.pojo.Emp;
import com.mybatis.study.utils.SqlSessionUtil;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

import java.util.List;

public class test {

    @Test
    public void testSelectAllEmp() {
        SqlSession sqlSession = SqlSessionUtil.getSqlSession();
        EmpMapper empMapper = sqlSession.getMapper(EmpMapper.class);
        List<Emp> list = empMapper.selectAllEmp();
        list.forEach(System.out::println);
    }
}

数据库表：

运行结果：