导入依赖：

        <!-- web依赖 -->
        <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>2.2.0</version>
        </dependency>
        <dependency>
            <groupId>org.apache.velocity</groupId>
            <artifactId>velocity</artifactId>
            <version>1.7</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis.generator</groupId>
            <artifactId>mybatis-generator-core</artifactId>
            <version>1.3.3</version>
        </dependency>
        <!-- 数据库连接池 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.1.10</version>
        </dependency>
        <!-- 使用SpringBoot-JPA进行数据查询 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <!-- mysql连接-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

注意事项：

application.yml配置文件

spring:
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    username: root
    password: root
    url: jdbc:mysql://localhost:3306/learning_test
#找到mapper
mybatis:
  mapper-locations: classpath:/mapper/*.xml

主函数上面添加mapper扫描

@SpringBootApplication
@MapperScan(basePackages = "com.example.testddemo.dao")
public class TestdemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(TestdemoApplication.class, args);
    }
}