一、导入依赖

一定要注意依赖版本的问题，不然会出现各种奇怪的问题。项目的整体结构如下：

<?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>
    <!--导入的依赖-->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.5</version>
    </parent>
    <groupId>org.example</groupId>
    <artifactId>sbpro</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <!--导入的依赖-->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!--集成mybatis要导入的依赖-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.1.0</version>
        </dependency>
    </dependencies>
</project>

二、配置yml文件

server:
  port: 8081
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/reggie?serverTimezone=Asia/Shanghai&useUnicode=true&characterEncoding=utf-8&zeroDateTimeBehavior=convertToNull&useSSL=false&allowPublicKeyRetrieval=true
    username: root
    password: wkt123.5
mybatis:
  mapper-locations: classpath:mapper/*.xml
  type-aliases-package: com.kt.entity

三、实体模型

package com.kt.entity;

public class User {

    private Long id;

    //姓名
    private String name;

    //手机号
    private String phone;

    //性别 0 女 1 男
    private String sex;

    //身份证号
    private String idNumber;

    //头像
    private String avatar;

    //状态 0:禁用，1:正常
    private Integer status;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPhone() {
        return phone;
    }

    public void setPhone(String phone) {
        this.phone = phone;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getIdNumber() {
        return idNumber;
    }

    public void setIdNumber(String idNumber) {
        this.idNumber = idNumber;
    }

    public String getAvatar() {
        return avatar;
    }

    public void setAvatar(String avatar) {
        this.avatar = avatar;
    }

    public Integer getStatus() {
        return status;
    }

    public void setStatus(Integer status) {
        this.status = status;
    }
}

四、Service

package com.kt.service;

import com.kt.entity.User;

import java.util.List;

public interface UserService {
    List<User> selectAll();
}

五、ServiceImpl

package com.kt.service.impl;

import com.kt.entity.User;
import com.kt.mapper.UserMapper;
import com.kt.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class UserServiceImpl implements UserService {

    @Autowired
    private UserMapper userMapper;

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

六、Mapper

package com.kt.mapper;

import com.kt.entity.User;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

@Mapper
public interface UserMapper {
    List<User> selectAll();
}

七、Mapper.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.kt.mapper.UserMapper">

    <select id="selectAll" resultType="User">
        SELECT * FROM user
    </select>

</mapper>

八、Controller

package com.kt.controller;

import com.kt.entity.User;
import com.kt.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/test")
public class TestController {

    @Autowired
    private UserService userService;

    @RequestMapping("/hello")
    public String testGet(){
        return "hello world";
    }


    @GetMapping("testMybatis")
    public List<User> testMybatis(){
        return userService.selectAll();
    }

}

九、浏览器访问

十、遇到的问题

	at org.apache.ibatis.type.TypeAliasRegistry.resolveAlias(TypeAliasRegistry.java:120) ~[mybatis-3.5.2.jar:3.5.2]
	at org.apache.ibatis.builder.BaseBuilder.resolveAlias(BaseBuilder.java:149) ~[mybatis-3.5.2.jar:3.5.2]
	at org.apache.ibatis.builder.BaseBuilder.resolveClass(BaseBuilder.java:116) ~[mybatis-3.5.2.jar:3.5.2]
	... 79 common frames omitted
Caused by: java.lang.ClassNotFoundException: Cannot find class: User
	at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:200) ~[mybatis-3.5.2.jar:3.5.2]
	at org.apache.ibatis.io.ClassLoaderWrapper.classForName(ClassLoaderWrapper.java:89) ~[mybatis-3.5.2.jar:3.5.2]
	at org.apache.ibatis.io.Resources.classForName(Resources.java:261) ~[mybatis-3.5.2.jar:3.5.2]
	at org.apache.ibatis.type.TypeAliasRegistry.resolveAlias(TypeAliasRegistry.java:116) ~[mybatis-3.5.2.jar:3.5.2]
	... 81 common frames omitted

原因：

mapper中的返回值类型写的是实体类类名，但是application.yml中未配置 type-aliases-package: com.kt.entity

解决：

在application.yml中配置type-aliases-package: com.kt.entity；或者配置返回值为全限定名