项目概述
基于 SpringBoot、MySQL 的增删查改
新建项目
- 新建数据库以及表
新建 java 项目
创建项目：
选择 Spring Initializr，选择 java 和 Maven，填写项目名字
SDK 选择 1.8，Java 选择 8
下一步，选择以下的配置：
配置 application.yml 文件
默认是application.properties,自己再新建一个application.yml即可
# 数据库地址
spring.datasource.url=jdbc:mysql:
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
# 自己的数据库名以及密码
spring.datasource.username=root
spring.datasource.password=root
# mybatis
# 对应的映射文件
mybatis.mapper-locations=classpath:mybatis/mapper
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架构
四个软件包：controller、service、mapper、entity
以及一个主应用入口：Application
- controller 对应控制器，用于对接接口的映射
- service 用于业务处理（当然目前比较简单，只作用于一个传递的功能）
- mapper 就是一些增删改查的接口
- entity 实体类，数据库中的每一张表对应于一个实体类（当然，可以有更详细的vo,bo之类的，只不过当前的demo比较简单，就一个数据库对应一个实体类啦）
- resource/mapper 用于编写实际sql的xml的地方
编写代码
先直接上所有文件
编写实体类 User
在包entity下，创建User类，然后提供与数据库对应的字段作为属性，现在使用lombok提供的注解，省略了很多构造方法
package com.lanke.player_demo.entity;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
@Data
@NoArgsConstructor
@AllArgsConstructor
@ToString
public class User {
private int id;
private String name;
private String password;
private String sex;
private int age;
private String phone;
}
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编写 mapper 接口
目前比较简单，只针对了一张表
package com.lanke.player_demo.mapper;
import com.lanke.player_demo.entity.User;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import java.util.List;
@Mapper
public interface UserMapper {
List<User> getAllUsers();
int addUser(User user);
int updUserById(User user);
User findUserById(@Param("id") int id);
int delUserById(@Param("id") int id);
}
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编写mapper.xml
文件在 Resource 目录下
<?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.lanke.player_demo.mapper.UserMapper">
<select id="getAllUsers" resultType="com.lanke.player_demo.entity.User">
select * from user
</select>
<insert id="addUser" >
insert into user
(name,password,sex,age,phone)
values (#{name},#{password},#{sex},#{age},#{phone})
</insert>
<update id="updUserById">
update user
set name = #{name},
sex = #{sex},
phone = #{phone},
age = #{age}
where id = #{id}
</update>
<select id="findUserById" resultType="com.lanke.player_demo.entity.User">
select * from user where id = #{id}
</select>
<delete id="delUserById">
delete from user where id = #{id}
</delete>
</mapper>
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注意：
- namespace命名空间，要指定你的mapper接口的完整路径
- 增删改查分别对应于四个标签 insert delete update select
- 每个sql对应于你的mapper接口中的方法，我们需要通过id去指定你当前的sql是哪个接口方法的
#{xxx} 这是mybatis提供的一种占位符，就是之前sql中学的 ？ 占位符resultType 结果类型，如果是实体类的话也需要通过指定完整的类路径
编写 service
package com.lanke.player_demo.service;
import com.lanke.player_demo.entity.User;
import com.lanke.player_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 List<User> getAllUsers(){
return userMapper.getAllUsers();
}
public int addUser(User user){
return userMapper.addUser(user);
}
public int updUserById(User user){
return userMapper.updUserById(user);
}
public User findUserById(int id){
return userMapper.findUserById(id);
}
public int delUserById(int id){
return userMapper.delUserById(id);
}
}
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编写 controller
package com.lanke.player_demo.controller;
import com.lanke.player_demo.entity.User;
import com.lanke.player_demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
import java.util.List;
@RestController
@RequestMapping("/user")
public class UserController {
@Autowired
private UserService userService;
@GetMapping("/list")
public List<User> getAllUsers(){
return userService.getAllUsers();
}
@PostMapping("/add")
public int addUser(@RequestBody User user){
return userService.addUser(user);
}
@PutMapping("/upd")
public int updUserById(@RequestBody User user){
return userService.updUserById(user);
}
@GetMapping("/find/{id}")
public User findUserById(@PathVariable("id") int id){
return userService.findUserById(id);
}
@DeleteMapping("/delete/{id}")
public int delUserById(@PathVariable("id") int id){
return userService.delUserById(id);
}
}
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@RestController 这个注解，可以将你的每个接口的返回值转换为一个json
@RequestMapping 用于指定接口的映射规则，这个的话，接着往下看就明白啦。
详情可以参阅：springbootWeb常用注解使用_springboot web 相关注解-CSDN博客
这样一个简单的增删查改就完成了。
但实际的后端开发仅仅这样是不够的，我们还需要写接口等等内容
Maven 配置
<?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>org.lanke</groupId>
<artifactId>player_demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>player_demo</name>
<description>player_demo</description>
<properties>
<java.version>1.8</java.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<spring-boot.version>2.7.6</spring-boot.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-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>2.3.0</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>com.mysql</groupId>
<artifactId>mysql-connector-j</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>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-dependencies</artifactId>
<version>${spring-boot.version}</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
<encoding>UTF-8</encoding>
</configuration>
</plugin>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<version>${spring-boot.version}</version>
<configuration>
<mainClass>org.lanke.player_demo.PlayerDemoApplication</mainClass>
<skip>true</skip>
</configuration>
<executions>
<execution>
<id>repackage</id>
<goals>
<goal>repackage</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
</project>
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MySQL 代码
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for user
-- ----------------------------
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
`id` int NOT NULL AUTO_INCREMENT COMMENT '主键ID',
`name` varchar(255) COMMENT '姓名',
`password` varchar(255) COMMENT '密码', -- 注意：通常密码不会以明文形式存储，这里仅作示例
`sex` enum('male', 'female', 'other') DEFAULT NULL COMMENT '性别', -- 使用ENUM类型限制性别输入
`age` int DEFAULT NULL COMMENT '年龄',
`phone` varchar(20) DEFAULT NULL COMMENT '电话', -- 电话号码通常不需要255个字符那么长
PRIMARY KEY (`id`) -- USING BTREE是多余的，InnoDB默认使用B-Tree索引
) ENGINE=InnoDB
AUTO_INCREMENT=1 -- 通常从1开始自增，除非有特定原因
CHARACTER SET=utf8mb4
COLLATE=utf8mb4_unicode_ci
COMMENT='用户信息表'
ROW_FORMAT=Dynamic;
-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES (1, '张三', '123456', '男', 25, '18888889999');
INSERT INTO `user` VALUES (3, 'robin', '123456', '男', 22, '14424567789');
SET FOREIGN_KEY_CHECKS = 1;
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常见问题 ：
出现依赖爆红错误
解决方法是选择/文件/使缓存失效，重启就可以了
参考资料
- springboot 如何编写增删改查后端接口，小白极速入门，附完整代码_教你写后端接口-CSDN博客
