启动类

//@MapperScan("")
//@SpringApplication
package com.example.demo;

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

@MapperScan("com.example.demo.mapper")
@SpringBootApplication
public class DemoApplication {

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

userMapper.java

//@Repository
package com.example.demo.mapper;

import com.example.demo.entity.User;
import org.springframework.stereotype.Repository;

import java.util.List;

@Repository
public interface UserMapper {
    //1.通过id查询用户信息
    User getUser(int id);
    //2.通过id删除用户信息
    int delete(int id);
    //3.更改用户信息
    int update(User user);
    //4.插入用户信息
    int save(User user);
    //5.查询所有用户信息
    List<User> selectAll();
}

userMapper.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.example.demo.mapper.UserMapper">
    <resultMap id="BaseResultMap" type="com.example.demo.entity.User">
        <result column="id" jdbcType="INTEGER" property="id" />
        <result column="name" jdbcType="VARCHAR" property="name" />
        <result column="salary" jdbcType="DOUBLE" property="salary" />
    </resultMap>
    <!--查询用户信息-->
    <select id="getUser" resultType="com.example.demo.entity.User">
        select * from water where id = #{id}
    </select>
    <!--删除用户信息-->
    <delete id="delete" parameterType="int">
        delete from water where id=#{id}
    </delete>
    <!--返回所有用户信息-->
    <select id="selectAll"  resultType="com.example.demo.entity.User">
        select * from water
    </select>

    <!--增加用户信息-->
    <insert id="save" parameterType="com.example.demo.entity.User" >
        insert into water
        <trim prefix="(" suffix=")" suffixOverrides="," >
            <if test="id != null" >
                id,
            </if>
            <if test="name != null" >
                name,
            </if>
            <if test="salary != null" >
                salary,
            </if>
        </trim>
        <trim prefix="values (" suffix=")" suffixOverrides="," >
            <if test="id != null" >
                #{id,jdbcType=INTEGER},
            </if>
            <if test="name != null" >
                #{name,jdbcType=VARCHAR},
            </if>
            <if test="salary != null" >
                #{salary,jdbcType=DOUBLE},
            </if>
        </trim>
    </insert>

    <!--根据id更改用户信息-->
    <update id="update" parameterType="com.example.demo.entity.User">
        update water
        <set >
            <if test="name != null" >
                name = #{name,jdbcType=VARCHAR},
            </if>
            <if test="salary != null" >
                salary = #{salary,jdbcType=DOUBLE},
            </if>
        </set>
        where id = #{id,jdbcType=INTEGER}
    </update>
</mapper>

userService.java

//@Service
//@Autowired
package com.example.demo.service;

import com.example.demo.entity.User;
import com.example.demo.mapper.UserMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class UserService {
    @Autowired
    private UserMapper userMapper;

    public User getUser(int id){    
        return userMapper.getUser(id);
    }

    public int delete(int id){
        return userMapper.delete(id);
    }

    public int update(User user){
        return userMapper.update(user);
    }

    public int save(User user){
        return userMapper.save(user);
    }

    public List<User>  selectAll(){
        return userMapper.selectAll();
    }
}

userController.java

//@RestController
//@RequestMapping
//@Autowired
package com.example.demo.controller;

import com.example.demo.entity.User;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;

import javax.xml.ws.Service;
import java.util.List;


@RestController
@RequestMapping("/seven")
public class UserController {
    @Autowired
    private UserService userService;
    //通过id得到用户信息
    @RequestMapping(value = "/getUser/{id}", method = RequestMethod.GET)
    public String getUser(@PathVariable int id){
        return userService.getUser(id).toString();
    }
    //通过id删除用户信息
    @RequestMapping(value = "/delete", method = RequestMethod.GET)
    public String delete(int id){
        int result = userService.delete(id);
        if(result >= 1){
            return "删除成功！";
        }else{
            return "删除失败！";
        }
    }
    //更改用户信息
    @RequestMapping(value = "/update", method = RequestMethod.GET)
    public String update(User user){
        int result = userService.update(user);
        if(result >= 1){
            return "更新成功！";
        }else{
            return "更新失败！";
        }
    }
    //插入用户信息
    @RequestMapping(value = "/insert", method = RequestMethod.GET)
    public int insert(User user){
        return userService.save(user);
    }
    //查询所有用户的信息
    @RequestMapping(value = "/selectAll")
    @ResponseBody   //理解为：单独作为响应体，这里不调用实体类的toString方法
    public List<User>  listUser(){
        return userService.selectAll();
    }
}

application.yml

spring:
  profiles:
    active: dev

application-dev.xml

#服务器端口配置
server:
  port: 8081

#数据库配置
spring:
  datasource:
    username: root
    password: root(密码)
    url: jdbc:mysql://localhost:3306/aa?useUnicode=true&characterEncoding=utf-8&nullCatalogMeansCurrent=true&useSSL=true&&serverTimezone=Asia/Shanghai
    driver-class-name: com.mysql.cj.jdbc.Driver

#mybatis配置
mybatis:
  mapper-locations: classpath:mapping/*.xml
  type-aliases-package: com.example.demo.entity

#showSQL
logging:
  level:
    com.example.demo.entity: debug