目的：创建一个新项目idea2022-Jesus，实现CRUD，该项目作为学习模版。

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STEP 1 项目创建

   1.1 新建Spring Initializr项目

  

   1.2 选择需要的依赖 springboot有2.7.2直接选272

  

STEP 2 配置更改

   2.1更改maven配置

   2.2 检查项目配置jdk、sdk、jre版本一致

   2.3 检查pom文件，Maven-Reload project构建下载包，不报红即可

   Maven的 Plugins 报红，执行命令mvn dependency:resolve-plugins，该命令的作用是：解决依赖关系，根据POM文件，下载或者更新该项目所依赖的库文件。
   pom文件会报版本不匹配，报错搜一下更新成适配版本就行了，下面是最终可用的pom文件。
pom.xml

<?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>

    <groupId>com.example</groupId>
    <artifactId>Jesus</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>Jesus</name>
    <description>Jesus</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>


    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <mybatis.spring.boot.version>2.1.3</mybatis.spring.boot.version>
        <java.version>1.8</java.version>
        <mysql.version>8.0.29</mysql.version>
        <druid.version>1.2.6</druid.version>
        <commons.lang.version>2.6</commons.lang.version>
    </properties>



    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jdbc</artifactId>
        </dependency>

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

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context-support</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <optional>true</optional>
        </dependency>

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>${mybatis.spring.boot.version}</version>
        </dependency>

        <dependency>
            <groupId>commons-lang</groupId>
            <artifactId>commons-lang</artifactId>
            <version>${commons.lang.version}</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>${mysql.version}</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>${druid.version}</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>

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

</project>

   2.4 删除properties文件，改用yaml配置文件

application.yml

spring:
  profiles:
    active: dev

application-dev.yml

server:
  port: 8080
 
spring:
  datasource:
    username: root【数据库名】
    password: zxy000123【数据库密码】
    url: jdbc:mysql://localhost:3306/zxy【库名称】?useUnicode=true&characterEncoding=utf-8&useSSL=true&serverTimezone=UTC
    driver-class-name: com.mysql.jdbc.Driver
 
mybatis:
  mapper-locations: classpath:mapping/*Mapper.xml
  type-aliases-package: com.example.entity
#showSql
logging:
  level:
    com:
      example:
        mapper : debug

   2.5 启动一下

STEP 3 实现业务CRUD

   3.1 库中建表

CREATE TABLE `user` (
  `id` int(32) NOT NULL AUTO_INCREMENT,
  `userName` varchar(32) NOT NULL,
  `passWord` varchar(50) NOT NULL,
  `realName` varchar(32) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

   3.2 项目结构

   新建controller、entity、mapper、service文件夹在com.example.jesusu下
   新建mapping在resurces下

   3.3 实体类、controller层、service层、mapper数据访问层、分别写代码

entity—User.java

package com.example.jesus.entity;

public class User {
    private Integer id;
    private String userName;
    private String passWord;
    private String realName;

    public Integer getId() {
        return id;
    }

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

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getPassWord() {
        return passWord;
    }

    public void setPassWord(String passWord) {
        this.passWord = passWord;
    }

    public String getRealName() {
        return realName;
    }

    public void setRealName(String realName) {
        this.realName = realName;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", userName='" + userName + '\'' +
                ", passWord='" + passWord + '\'' +
                ", realName='" + realName + '\'' +
                '}';
    }
}

Controller—UserController.java

package com.example.jesus.controller;

import com.example.jesus.entity.User;
import com.example.jesus.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;



@RestController
@RequestMapping("/testBoot")
public class UserController {

    @Autowired
    private UserService userService;

    @RequestMapping("getUser/{id}")
    public String GetUser(@PathVariable int id){
        return userService.Sel(id).toString();
    }
}

Service—UserService.java

package com.example.jesus.service;

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


@Service
public class UserService {
    @Autowired
    UserMapper userMapper;
    public User Sel(int id){
        return userMapper.Sel(id);
    }
}

Mapper—UserMapper.java

package com.example.jesus.mapper;

import com.example.jesus.entity.User;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;


@Repository
public interface UserMapper {

    User Sel(int id);
}

Mapper—UserMapping.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.jesus.mapper.UserMapper">

    <resultMap id="BaseResultMap" type="com.example.entity.User">
        <result column="id" jdbcType="INTEGER" property="id" />
        <result column="userName" jdbcType="VARCHAR" property="userName" />
        <result column="passWord" jdbcType="VARCHAR" property="passWord" />
        <result column="realName" jdbcType="VARCHAR" property="realName" />
    </resultMap>

    <select id="Sel" resultType="com.example.entity.User">
        select * from user where id = #{id}
    </select>

</mapper>

   3.4 启动类增加注解

   加上注解用于给出需要扫描的mapper文件路径
   @MapperScan(“com.example.mapper”)

package com.example.jesus;

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


@MapperScan("com.example.jesus.mapper") //扫描的mapper
@SpringBootApplication
public class JesusApplication {

    public static void main(String[] args) {
        SpringApplication.run(JesusApplication.class, args);
        System.out.println("启动Jesus项目成功");
    }

}