修改配置文件:

<?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>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.5.RELEASE</version>


    </parent>
    <packaging>jar</packaging>

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

    <properties>
        <java.version>1.8</java.version>
        <maven-jar-plugin.version>3.1.1</maven-jar-plugin.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator</artifactId>
            <version>1.3.3</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.0.0</version>
        </dependency>


        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper-spring-boot-starter</artifactId>
            <version>1.2.10</version>
        </dependency>
        <!-- 阿里巴巴 druid数据源 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.16</version>
        </dependency>

        <!-- 阿里巴巴json包 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.58</version>
        </dependency>


    </dependencies>


    <build>
        <plugins>

            <!-- 自动生成代码插件 -->
            <plugin>
                <groupId>org.mybatis.generator</groupId>
                <artifactId>mybatis-generator-maven-plugin</artifactId>
                <version>1.3.2</version>
                <configuration>
                    <!--配置文件的位置-->
                    <configurationFile>src/main/resources/generatorConfig.xml</configurationFile>
                    <verbose>true</verbose>
                    <overwrite>true</overwrite>
                </configuration>
                <executions>
                    <execution>
                        <id>Generate MyBatis Artifacts</id>
                        <goals>
                            <goal>generate</goal>
                        </goals>
                    </execution>
                </executions>
                <dependencies>
                    <dependency>
                        <groupId>org.mybatis.generator</groupId>
                        <artifactId>mybatis-generator-core</artifactId>
                        <version>1.3.2</version>
                    </dependency>
                </dependencies>
            </plugin>

        </plugins>

        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.yml</include> <include>**/*.xml</include>
                </includes>
                <filtering>false</filtering>
            </resource>
        </resources>
    </build>


</project>

在resources文件夹里添加generatorConfig.xml文件,下载一个mysql连接jar包,放在对应位置。
官方文档

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE generatorConfiguration
        PUBLIC "-//mybatis.org//DTD MyBatis Generator Configuration 1.0//EN"
        "http://mybatis.org/dtd/mybatis-generator-config_1_0.dtd">

<generatorConfiguration>
    <!--mysql 连接数据库jar 这里选择自己本地位置;
    如果不知道maven本地仓库地址,可以使用EveryThing工具全局搜索mysql-connector-java,找到jar包位置;
    也可以手动下载一个jar放在指定位置,进行引用。
    -->
    <classPathEntry location="F:/mysql-connector-java-5.1.47.jar"/>

    <context id="testTables" targetRuntime="MyBatis3">
        <commentGenerator>
            <!-- 是否去除自动生成的注释,true:是,false:-->
            <property name="suppressAllComments" value="true"/>
        </commentGenerator>

        <!--数据库连接的信息:驱动类、连接地址、用户名、密码 -->
        <jdbcConnection driverClass="com.mysql.jdbc.Driver"
                        connectionURL="jdbc:mysql://localhost:3306/***" userId="root"
                        password="">
        </jdbcConnection>

        <!-- 默认false,把JDBC DECIMAL 和 NUMERIC 类型解析为 Integer,为 true时把JDBC DECIMAL 和
           NUMERIC 类型解析为java.math.BigDecimal -->
        <javaTypeResolver>
            <property name="forceBigDecimals" value="false"/>
        </javaTypeResolver>

        <!-- 指定javaBean生成的位置
            targetPackage:生成的类要放的包,真实的包受enableSubPackages属性控制;
            targetProject:目标项目,指定一个存在的目录下,生成的内容会放到指定目录中,如果目录不存在,MBG不会自动建目录
         -->
        <javaModelGenerator targetPackage="com.xiling.dao.model" targetProject="src/main/java">
            <!-- 在targetPackage的基础上,根据数据库的schema再生成一层package,最终生成的类放在这个package下,默认为false;如果多个数据库改为true分目录 -->
            <property name="enableSubPackages" value="false"/>
            <!-- 设置是否在getter方法中,对String类型字段调用trim()方法 -->
            <property name="trimStrings" value="true"/>
        </javaModelGenerator>

        <!--  指定mapper映射文件生成的位置
           targetPackage、targetProject同javaModelGenerator中作用一样-->
        <sqlMapGenerator targetPackage="com.**.dao.mapper" targetProject="src/main/java">
            <property name="enableSubPackages" value="false"/>
        </sqlMapGenerator>

        <!-- 指定mapper接口生成的位置
         targetPackage、targetProject同javaModelGenerator中作用一样
         -->
        <javaClientGenerator type="XMLMAPPER" targetPackage="com.***.dao" targetProject="src/main/java">
            <property name="enableSubPackages" value="false"/>
        </javaClientGenerator>

        <!-- 指定数据库表
        domainObjectName:生成的domain类的名字,当表名和domain类的名字有差异时一定要设置,如果不设置,直接使用表名作为domain类的名字;
        可以设置为somepck.domainName,那么会自动把domainName类再放到somepck包里面;
        -->
        <table tableName="******" domainObjectName="*****"></table>
     

    </context>
</generatorConfiguration>

同目录文件夹下添加mysql配置,mybatis配置文件application.yml

server:
  port: 8080

spring:       
  datasource:
    name: mysql_test
    type: com.alibaba.druid.pool.DruidDataSource
    #druid相关配置
    druid:
      #监控统计拦截的filters
      filters: stat
      driver-class-name: com.mysql.cj.jdbc.Driver
      #基本属性
      url: jdbc:mysql://localhost:3306/xxx?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&serverTimezone=UTC
      username: root
      password: xxx
      #配置初始化大小/最小/最大
      initial-size: 1
      min-idle: 1
      max-active: 20
      #获取连接等待超时时间
      max-wait: 60000
      #间隔多久进行一次检测,检测需要关闭的空闲连接
      time-between-eviction-runs-millis: 60000
      #一个连接在池中最小生存的时间
      min-evictable-idle-time-millis: 300000
      validation-query: SELECT 'x'
      test-while-idle: true
      test-on-borrow: false
      test-on-return: false
      #打开PSCache,并指定每个连接上PSCache的大小。oracle设为true,mysql设为false。分库分表较多推荐设置为false
      pool-prepared-statements: false
      max-pool-prepared-statement-per-connection-size: 20 

##
mybatis:
  mapper-locations: classpath:com/**/dao/mapper/.xml  
  #注意:一定要对应mapper映射xml文件的所在路径
  type-aliases-package: com.xiling.dao.model  # 注意:对应实体类的路径
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl

#pagehelper
pagehelper:
  helperDialect: mysql
  reasonable: true
  supportMethodsArguments: true
  params: count=countSql
  #returnPageInfo: check
    

在maven设置里这样写,运行即可。