SpringBoot+Mybatis框架实现增删改查功能

从啥也不会开始学java和相关的框架，又是一个胎教系列哈哈哈

原链接：

https://segmentfault.com/a/1190000023120991

我只在原作者基础上做了很小很小的修改，原文已经写得很好了，有点基础的建议去看原教程～！

胎教开始

• 新建项目->选择spring initializr项目

• 贴pom

<?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>2.5.3</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>


    <groupId>改成自己的包名 我用的com.nana</groupId>
    <artifactId>改成自己的项目名 我用的cloud2021</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>cloud2021</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>


    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <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>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
<!--
            <scope>runtime</scope>
-->
        </dependency>
        
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

• 把resource下的application改成yml格式->yml文件中包含：server port/spring/mybatis具体如下

// 遇到的坑：如果建立的是maven项目 小绿叶有可能不出现 一般的解决办法：https://www.pianshen.com/article/12311050998/

// 要注意： application.yml要在resources文件夹下

// 用Spring Initailzr永久解决此问题

// 严格对齐 讲究缩进

// 以下配置数据库：username&password:数据库的用户名密码

// url：一般是复制的链接的数据库地址 其中jdbc：使用jdbc驱动方式连接数据库；mysql：链接的数据类型是mysql；localhost：数据库具体地址；3306:数据库端口号；testpay数据库名；characterEncoding：编码格式；serveTimezone设置时区；useSSL = true并提供信任库以进行服务器证书验证

// driver-class-name： 一般是这个不会改

// mybatis映射

// logging记录

server:
  port: 8080  //也可以改 测试的时候写相应的端口号就行

spring:
  datasource:
    username: //换成自己的数据库
    password: //换成自己的数据库
    url: jdbc:mysql://localhost:3306/换成自己的数据名?useUnicode=true&characterEncoding=utf-8&useSSL=true&serverTimezone=UTC
    driver-class-name: com.mysql.cj.jdbc.Driver

mybatis:
  mapper-locations: classpath:mapping/*Mapper.xml
  type-aliases-package: com.nana.cloud2021.entity.User   //改成自己的包名

logging:
  level:
    com:
      example:
        mapper : debug

/

• 创建表：这个也很简单 在mybatis里创建好链接然后右键“运行sql文件”

// 删除已存在的表格 DROP TABLE IF EXISTS `表格名`

// USING BTREE：搜索用b树

// AUTO_INVCREMENT = 1 设定新表从1开始自增

// 编码是utf8

// ROW_FORMAT行记录结构类型

DROP TABLE IF EXISTS `表格名`;
CREATE TABLE `表格名`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `password` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  `address` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 1 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

/

• 写主启动类：为了让程序引用得出mysql表

//为了让程序和mysql联系起来

// @MapperScan("com.nana.cloud2021.mapper") 扫描的mapper

package 包名;

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

@MapperScan("包名.mapper") //扫描的mapper
@SpringBootApplication
public class Cloud2021Application {

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

/

• 写ENTITY层或POJO层

// 第一步：定义User类

// 第二步：写一写这个类可以进行的一些操作

// 这里面id username password address都是和数据库表相对应的

// 下面一些函数的操作在本次项目中其实没用到

package 包名.entity;


public class User {
    private Integer id;
    private String username;
    private String password;
    private String address;

    public User(Integer id, String username, String password, String address) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.address = address;
    }

    public Integer getId()
    {
        return id;
    }

    public String getUsername()
    {
        return username;
    }

    public String getPassword()
    {
        return password;
    }

    public String getAddress()
    {
        return address;
    }

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

    public void setUsername(String username)
    {
        this.username = username;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public void setAddress(String address)
    {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

/

• 写DAO层或MAPPER层

// *要用到：entity层

// 本质是数据库与程序的接口

package com.nana.cloud2021.entity;


public class User {
    private Integer id;
    private String username;
    private String password;
    private String address;

    public User(Integer id, String username, String password, String address) {
        this.id = id;
        this.username = username;
        this.password = password;
        this.address = address;
    }

    public Integer getId()
    {
        return id;
    }

    public String getUsername()
    {
        return username;
    }

    public String getPassword()
    {
        return password;
    }

    public String getAddress()
    {
        return address;
    }

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

    public void setUsername(String username)
    {
        this.username = username;
    }

    public void setPassword(String password)
    {
        this.password = password;
    }

    public void setAddress(String address)
    {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", password='" + password + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

/

• 配置MAPPER

/

// xml格式->前面写了<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"  这些，所以后面用到的这些都是与mybatis相应的格式，resultMap：结果格式；select对应mysql语句中的SELECT；相互对应

// 踩过的坑：程序找不到对应的mysql表

// 解决方法：重新建程序 把名字改得统一一点 问题主要是程序名称类型不匹配，但是实在查不出哪里不匹配

// trim标签的功能简单来说就是自定义格式拼凑SQL语句

// prefix：表示在trim包裹的SQL前添加指定内容

// suffix：表示在trim包裹的SQL末尾添加指定内容

// prefixOverrides：表示去掉（覆盖）trim包裹的SQL的指定首部内容

// suffixOverrides：表示去掉（覆盖）trim包裹的SQL的指定尾部内容

<?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="包名.mapper.UserMapper">

    <resultMap id="BaseResultMap" type="包名.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="address"/>
    </resultMap>

    <select id="Sel" resultType="包名.entity.User">
        select * from user where 1=1
        <if test="user.id != null">
            AND id = #{user.id}
        </if>
    </select>

    <insert id="Add" parameterType="包名.entity.User">
        INSERT INTO user
        <trim prefix="(" suffix=")" suffixOverrides=",">
            <if test="user.username != null">
                username,
            </if>
            <if test="user.password != null">
                password,
            </if>
            <if test="user.address != null">
                address,
            </if>
        </trim>
        <trim prefix="VALUES (" suffix=")" suffixOverrides=",">
            <if test="user.username != null">
                #{user.username,jdbcType=VARCHAR},
            </if>
            <if test="user.password != null">
                #{user.password,jdbcType=VARCHAR},
            </if>
            <if test="user.address != null">
                #{user.address,jdbcType=VARCHAR},
            </if>
        </trim>
    </insert>

    <update id="Update" parameterType="包名.entity.User">
        UPDATE user
        <set>
            <if test="user.username != null">
                username = #{user.username},
            </if>
            <if test="user.password != null">
                password = #{user.password},
            </if>
            <if test="user.address != null">
                address = #{user.address},
            </if>
        </set>
        WHERE
        id=#{user.id}
    </update>

    <delete id="Delete"  parameterType="包名.entity.User">
        DELETE FROM user WHERE id = #{user.id}
    </delete>

</mapper>

/

• 写SERVICE与SERVICEIMPL

// 一般来说SERVICE是一个接口而具体的功能实现在SERVICEIMPL中

// 即SERVICE叫接口层 SERVICEIMPL叫实现类

// SERVICE层中：是个接口所以是interface

// *要用到entity层

package 包名.service;


import 包名.entity.User;

public interface UserService {
    User Sel(User user);

    String Add(User user);

    String Update(User user);

    String Delete(User user);
}

// IMPL层中：是具体的实现类 所以是CLASS 然后implements

// 本质还是对接口函数进行实现，在这里可以给项目添加许多具体功能

// *用到了service entity mapper

package 包名.service.serviceImpl;

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

@Service
public class UserServiceImpl implements UserService
{

    @Autowired
    UserMapper userMapper;

    public User Sel(User user)
    {

        return userMapper.Sel(user);
    }

    public String Add(User user)
    {
/*        System.out.println(user.getUsername());
        user.setUsername("lj"+"====");*/
        int a = userMapper.Add(user);
        if (a == 1) {
            return "添加成功";
        } else {
            return "添加失败";
        }
    }

    public String Update(User user)
    {
        int a = userMapper.Update(user);
        if (a == 1) {
            return "修改成功";
        } else {
            return "修改失败";
        }
    }

    public String Delete(User user)
    {
        int a = userMapper.Delete(user);
        if (a == 1) {
            return "删除成功";
        } else {
            return "删除失败";
        }
    }

}

/

• 写CONTROLLER

// 处理前台发送的语句

// 用到的包entity service

// @RestControler = @ResponseBody+@Controller

// 其中Controller处理http请求

//

// @RequestMapping仅作用在处理器方法上

// @RequestMapping仅作用在类级别上

// @RequestMapping作用在类级别和处理器方法上

package 包名.controller;

import 包名.entity.User;

import 包名.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;


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

    @Autowired
    private UserService userService;

    @RequestMapping(value = "/selectUserByid", produces = "application/json;charset=UTF-8", method = RequestMethod.GET)
    @ResponseBody
    public String GetUser(User user){
        return userService.Sel(user).toString();
    }

    @RequestMapping(value = "/add", produces = "application/json;charset=UTF-8", method = RequestMethod.GET)
    public String Add(User user){
        return userService.Add(user);
    }

    @RequestMapping(value = "/update", produces = "application/json;charset=UTF-8", method = RequestMethod.GET)
    public String Update(User user){
        return userService.Update(user);
    }

    @RequestMapping(value = "/delete", produces = "application/json;charset=UTF-8", method = RequestMethod.GET)
    public String Delete(User user){
        return userService.Delete(user);
    }
}

到这里整个程序的代码就都贴上去了，先看看有没有贴错或者手滑打错，有红色bug的话可以百度改一改，然后打开网页开始测试

增：localhost:8080/test/add?username=username&password=1111&address=1111

删：localhost:8080/test/delete?id=1

改：localhost:8080/test/update?id=1&username=newname&password=1111&address=1111

查：localhost:8080/test/selectUserByid?id=1

没有问题的话还是可以得到相应反馈的。

总结一下网页端的处理过程：

这张图是从网页用户角度做的，很清晰

图源这里： https://blog.youkuaiyun.com/congweijing/article/details/82499627

总结：Controller层调用Service层的具体功能方法，Service层调用Mapper层的方法，其中调用的参数是使用Entity层进行传递的

所以从建立工程的角度上，过程是反过来的

布置完pom，小改启动类之后，先entity再mapper再service最后controller

下面这个链接讲了一下这些层之间的联系和作用，很适合胎教学习

https://zhuanlan.zhihu.com/p/109164753

以上。

欢迎大家指教讨论！