01、新建一个springboot项目

选择依赖和版本

SpringBoot整合lombok

lombok是一个快速生成JAVAbean的一个工具工程和生成日志的工具。未来给我们提供了很大的遍历。

需要在idea中安装插件和pom.xml中进行依赖才可以使用生效：

pom.xml依赖如下：

 <dependency>     <groupId>org.projectlombok</groupId>     <artifactId>lombok</artifactId>     <optional>true</optional> </dependency> 复制代码

SpringBoot在依赖的过程，为什么有的要加版本号，有的不加？

 <dependency>     <groupId>org.springframework.boot</groupId>     <artifactId>spring-boot-starter-web</artifactId> </dependency>  <dependency>     <groupId>MySQL</groupId>     <artifactId>mysql-connector-java</artifactId>     <version>8.0.27</version> </dependency>  <dependency>     <groupId>com.baomidou</groupId>     <artifactId>MyBatis-plus-boot-starter</artifactId>     <version>3.5.2</version> </dependency>  <dependency>     <groupId>org.projectlombok</groupId>     <artifactId>lombok</artifactId>     <optional>true</optional> </dependency> 复制代码

• mysql
• mybatis-plus 都不属于springboot父工程管理，自然必须把自己的version加上去！

SpringBoot整合Mybatis-Plus和数据源

1、在pom.xml中依赖如下：

 <dependency>     <groupId>mysql</groupId>     <artifactId>mysql-connector-java</artifactId>     <version>8.0.27</version> </dependency>  <dependency>     <groupId>com.baomidou</groupId>     <artifactId>mybatis-plus-boot-starter</artifactId>     <version>3.5.2</version> </dependency> 复制代码

2、准备一个数据库表kss_user

 CREATE TABLE `kss_user` (   `id` int NOT NULL AUTO_INCREMENT,   `user_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,   `password` varchar(255) DEFAULT NULL,   `real_name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,   `gender` int DEFAULT NULL,   `birthday` date DEFAULT NULL,   `create_time` datetime DEFAULT NULL,   `update_time` datetime DEFAULT NULL,   PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci; 复制代码

3、配置数据源和mybatis配置

在项目的resource目录下的Application.yaml配置如下：

 server:   port: 8080  # 数据源配置 spring:   application:     name: pug-springboot-ssm   datasource:     type: com.zaxxer.hikari.HikariDataSource     driver-class-name: com.mysql.cj.jdbc.Driver     url: jdbc:mysql://127.0.0.1:3306/ssm_db?serverTimezone=GMT%2b8&useUnicode=true&useSSL=false&characterEncoding=UTF-8     username: root     password: 123456     hikari:       connection-timeout: 60000       validation-timeout: 3000       idle-timeout: 60000       login-timeout: 5       max-lifetime: 60000       maximum-pool-size: 30       minimum-idle: 10       read-only: false   # mybatis-plus配置 mybatis-plus:   configuration:     log-impl: org.Apache.ibatis.logging.stdout.StdOutImpl   mapper-locations:     - classpath*:/mapper/*.xml 复制代码

4、在resource新建一个mapper文件用来存放mybatis的xml文件

5、springboot整合mybatis-plus

 package com.ksd.pug;  import org.mybatis.spring.annotation.MapperScan; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication;  @SpringBootApplication @MapperScan("com.ksd.pug.mapper") public class PugSpringbootSsmApplication {      public static void main(String[] args) {         SpringApplication.run(PugSpringbootSsmApplication.class, args);     }  } 复制代码

SpringBoot实现对用户表的CRUD操作

01、pojo

 package com.ksd.pug.pojo;  import com.baomidou.mybatisplus.annotation.IdType; import com.baomidou.mybatisplus.annotation.TableId; import com.baomidou.mybatisplus.annotation.TableName; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import lombok.ToString;  import java.io.Serializable; import java.util.Date;  @Data @AllArgsConstructor @NoArgsConstructor @ToString @TableName("kss_user") public class User implements Serializable {      @TableId(type = IdType.AUTO)     private Integer id;     private String username;     private String password;     private String realName;     private Integer gender;     private Date birthday;  } 复制代码

02、mapper

 package com.ksd.pug.mapper;  import com.baomidou.mybatisplus.core.mapper.BaseMapper; import com.ksd.pug.pojo.User;  public interface UserMapper extends BaseMapper<User> { } 复制代码

03、service和serviceImpl

 package com.ksd.pug.service;  import com.baomidou.mybatisplus.extension.service.IService; import com.ksd.pug.pojo.User;  public interface IUserService extends IService<User> { } 复制代码

 package com.ksd.pug.service;  import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl; import com.ksd.pug.mapper.UserMapper; import com.ksd.pug.pojo.User; import lombok.extern.slf4j.Slf4j; import org.springframework.stereotype.Service;  @Slf4j @Service public class IUserServiceImpl extends ServiceImpl<UserMapper, User> implements IUserService { } 复制代码

04、controller

 package com.ksd.pug.controller;   import com.baomidou.mybatisplus.core.conditions.query.LambdaQueryWrapper; import com.baomidou.mybatisplus.core.metadata.IPage; import com.baomidou.mybatisplus.extension.plugins.pagination.Page; import com.ksd.pug.config.exception.BusinessException; import com.ksd.pug.config.results.Code; import com.ksd.pug.config.results.Result; import com.ksd.pug.pojo.User; import com.ksd.pug.service.IUserService; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.*;  @RestController @RequestMapping("/user") public class UserController {      @Autowired     private IUserService userService;      @PostMapping     public Result save(User user){         boolean flag = userService.saveOrUpdate(user);         return new Result(flag ? Code.SAVE_OK:Code.SAVE_ERROR);     }      @PutMapping     public Result update(User user){         boolean flag = userService.updateById(user);         return new Result(flag ? Code.UPDATE_OK:Code.UPDATE_ERROR);     }      @DeleteMapping("/{id}")     public Result delete(Integer id){         boolean flag = userService.removeById(id);         return new Result(flag ? Code.DELETE_OK:Code.DELETE_ERROR);     }      @GetMapping("/{id}")     public Result get(@PathVariable("id")Integer id) throws BusinessException {         User user = userService.getById(id);         // 模拟出现异常，使用条件控制，便于测试结果         if (id == 10) {             throw new BusinessException("查询出错了，请重试！",Code.GET_ERROR);         }         return new Result(null != user ? Code.GET_OK :Code.GET_ERROR,user);     }      @GetMapping("/{pageNo}/{pageSize}")     public Result getAll(@PathVariable Integer pageNo,@PathVariable Integer pageSize){         // 1、设置分页         Page page = new Page<>(pageNo,pageSize);         // 2、设置条件         LambdaQueryWrapper<User> lambdaQueryWrapper = new LambdaQueryWrapper<>();         // 3、查询分页返回         IPage page1 = userService.page(page, lambdaQueryWrapper);         return new Result(null != page1 ? Code.GET_OK :Code.GET_ERROR,page1);     }   } 复制代码

Mybatis-Plus的分页失效问题

 @Configuration public class MybatisPlusConfig {      /**      * 新的分页插件,一缓和二缓遵循mybatis的规则,需要设置 MybatisConfiguration#useDeprecatedExecutor = false 避免缓存出现问题(该属性会在旧插件移除后一同移除)      */      @Bean     public MybatisPlusInterceptor mybatisPlusInterceptor() {         MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();         interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.MYSQL));         return interceptor;     }  } 复制代码

Mybatis-Plus的创建时间和更新时间回填问题

1. 定义个回填配置类

 @Slf4j @Component  public class MyMetaObjectHandler implements MetaObjectHandler {      @Override     public void insertFill(MetaObject metaObject) {         log.info("start insert fill...");         //default MetaObjectHandler setFieldValByName(String fieldName, Object fieldVal, MetaObject metaObject)         this.setFieldValByName("createTime",new Date(),metaObject);         this.setFieldValByName("updateTime",new Date(),metaObject);      }      @Override     public void updateFill(MetaObject metaObject) {         this.setFieldValByName("updateTime",new Date(),metaObject);     } } 复制代码

2. 在pojo中使用@TableFiled(fill=xxx)指定回填触发方法

 package com.ksd.pug.pojo;  import com.baomidou.mybatisplus.annotation.*; import lombok.AllArgsConstructor; import lombok.Data; import lombok.NoArgsConstructor; import lombok.ToString;  import java.io.Serializable; import java.util.Date;  @Data @AllArgsConstructor @NoArgsConstructor @ToString @TableName("kss_user") public class User implements Serializable {      @TableId(type = IdType.AUTO)     private Integer id;     private String userName;     private String password;     private String realName;     private Integer gender;     private Date birthday;     @TableField(fill = FieldFill.INSERT)     private Date createTime;     @TableField(fill = FieldFill.INSERT_UPDATE)     private Date updateTime;  } 复制代码

数据库级别的解决方案

首先将字段设置为timestamp，然后设置不是null，根据当前时间戳更新，在这里注意我们的create_time是不根据当前时间戳更新的！这种方式虽然可以但是不建议！

在mysql低版本的时候可能会出现一个问题，你的sql语句无法导入，而导致这个的原因是有的他只可以设置一个timestamp（在这里提示：mysql5.7 、mysql8.0是可以的！）

Mybatis-Plus是怎么做到不写sql但是可以实现CRUD操作

• 背后绝对是拼接SQL语句，然后调用mybatis底层执行sql。

具体需要学习mp！

作者：Nakano_May
链接：
https://juejin.cn/post/7183739358883610680