一、创建Maven工程

二、pom.xml文件

引入 MyBatis Plus 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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.4.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.md</groupId>
    <artifactId>01-hello</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>01-hello</name>
    <description>Demo project for Spring Boot</description>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
<!--MysqL版本-->
        <dependency>
            <groupId>MysqL</groupId>
            <artifactId>MysqL-connector-java</artifactId>
            <scope>5.1.9</scope>
        </dependency>

        <!--1. 加入依赖-->
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.3.1.tmp</version>
        </dependency>


        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

三、创建实体类

首先数据库中有对应的字段

通过lombok

package com.md.entity;

import lombok.Data;

/**
 * @author md
 * @Desc
 * @date 2020/10/26 15:38
 */

// 2. 使用这个注解直接生成set和get方法
@Data
public class Student {

    private Integer id;
    private String name;
    private Integer age;

}

四、Mapper接口

package com.md.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.md.entity.Student;

/**
 * @author md
 * @Desc
 * @date 2020/10/26 15:46
 */

// 3. 接口继承BaseMapper并指定类型
public interface StudentMapper extends BaseMapper<Student> {

}

五、主配置

spring.datasource.driver-class-name=com.MysqL.cj.jdbc.Driver
spring.datasource.url=jdbc:MysqL://localhost:3306/springboot?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=UTF-8

spring.datasource.username=root
spring.datasource.password=123456


# 专门用于打印日志
mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl

六、启动类

package com.md;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
// 4. mapper扫描
@MapperScan("com.md.mapper")
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class,args);
    }

}

七、测试

package com.md;

import com.md.mapper.StudentMapper;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class ApplicationTests {

    @Autowired
    private StudentMapper mapper;

    // 5. 测试，查询数据
    @Test
    void contextLoads() {
        // 不加条件全部查询，把每个对象迭代出来
        mapper.selectList(null).forEach(System.out::println);
    }

}

这样就可以把对应的数据查询出来了