1：application.yml文件配置

server:
  port: 8088
  servlet:
    context-path: /test
spring:
  datasource:
    name: text  #????
    url: jdbc:mysql://localhost:3306/dsdd?serverTimezone=GMT&useUnicode=true&characterEncoding=utf-8&useSSL=true
    username: root  #??
    password: root  #??
    #要添加mysql-connector-java依赖
    driver-class-name: com.mysql.cj.jdbc.Driver  #????com.mysql.jdbc.Driver


mybatis-plus:
  #这个作用是扫描xml文件生效可以和mapper接口文件使用，如果不加这个就是启动类加了@MapperScan
  #或者在mapper接口添加@Mapper都无法使用xml中的sql语句和默认的BaseMapper的语句
  mapper-locations: classpath*:com/example/poi/mapper/**/xml/*Mapper.xml
  global-config:
    # 关闭MP3.0自带的banner
    banner: false
    db-config:
      #主键类型
      id-type: ASSIGN_ID
      # 默认数据库表下划线命名
      table-underline: true
  configuration:
    # 这个配置会将执行的sql打印出来，在开发或测试的时候可以用
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    # 返回类型为Map,显示null对应的字段
    call-setters-on-nulls: true

2：pom.xml文件依赖管理，web服务必须按以下依赖

<?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>2.2.7.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>poi</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>poi</name>
    <description>poi</description>
    <properties>
        <java.version>8</java.version>
    </properties>
    <dependencies>
    
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.1</version>
        </dependency>

        <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>8.0.13</version>
        </dependency>
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        
    </dependencies>

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

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

    </build>

</project>

注意：1-使用web服务controller访问必须导入以下依赖

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

注意：2-使用mybatis必须导入以下依赖

        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.1</version>
        </dependency>

注意：3-打开项目的target目录，观察里面是否有对应的××Mapper.xml文件，若没有，则在pom.xml文件中加入如下配置

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

3：项目结构图

4：启动类

package com.example.poi;

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

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

5：controller类

package com.example.poi.controller;

import com.example.poi.service.ITest;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;
import javax.servlet.http.HttpServletResponse;

/**
 * @Author xu
 * @create 2023/7/5 01
 */

@RestController
@RequestMapping("/customDemo")
public class DemoTwoController {

    @Resource
    ITest iTest;

    @GetMapping("/export")
    public void exportExcel(HttpServletResponse response) {

        String age = "20";
        String phone = iTest.getPhone(age);
    }
}

6：service和impl类

package com.example.poi.service;

import com.baomidou.mybatisplus.extension.service.IService;
import com.example.poi.entity.EntityDemo;

/**
 * @Author xu
 * @create 2023/7/14 22
 */
public interface ITest extends IService<EntityDemo> {

    String getPhone(String age);

}

package com.example.poi.service.impl;

import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.poi.entity.EntityDemo;
import com.example.poi.mapper.TestMapper;
import com.example.poi.service.ITest;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;

/**
 * @Author xu
 * @create 2023/7/14 22
 */
@Service
public class TestImpl extends ServiceImpl<TestMapper, EntityDemo> implements ITest {

    @Resource
    TestMapper testMapper;

    @Override
    public String getPhone(String age) {

        EntityDemo list = testMapper.selectName();

        this.baseMapper.selectOne(new LambdaQueryWrapper<EntityDemo>().eq(EntityDemo::getAge, age));


        return "entityDemo.getPhone()";
    }
}

7：mapper类和xml文件

package com.example.poi.mapper;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.poi.entity.EntityDemo;

/**
 * @Author xu
 * @create 2023/7/14 22
 */
//@Mapper
public interface TestMapper  extends BaseMapper<EntityDemo> {


    //@Select("select * from entity_demo where age='20'")
    EntityDemo selectName();
}

<?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.example.poi.mapper.TestMapper">

    <select id="selectName" resultType="com.example.poi.entity.EntityDemo">
        select * from entity_demo where age='20'
    </select>
</mapper>