SpringBoot Entity中枚举类型详细使用介绍

简介方案对比

本处列举表示类型或状态的常用方法的对比。

法1：使用数字表示（不推荐）

//1：支付宝支付；2：微信支付；3：银行卡支付
private Integer payType;

这种方法的缺点：可读性极差，排查问题也麻烦。比如：前端页面上看到了2这个类型，还要看接口文档或者问后端这是什么意思，浪费时间！

法2：使用字符串表示（不推荐）

//ALIPAY：支付宝；WECHAT_PAY：微信；BANK_CARD_PAY：银行卡支付
private String payType;

这种方式比法1好一些了，提高了数据库的可读性和排查问题速度。

缺点：难以控制不允许数据库的pay_type为空字符串这种情况；支持的类型没有限制死，前端传个其他的字符串也能存入数据库。

法3：使用枚举表示（推荐）

枚举是这种场景最好的方案（枚举本身就是为了表示可穷举类型而发明出来的！）。

定义一个枚举类

package com.example.demo.order.enums;
import lombok.Getter;
@Getter
public enum PayTypeEnum {
    ALIPAY("支付宝"),
    WECHAT_PAY("微信支付"),
    BANK_CARD_PAY("银行卡支付"),
    ;
    private final String description;
    PayTypeEnum(String description) {
        this.description = description;
    }
}

Entity中定义枚举类型字段

private PayTypeEnum payType;

优点

可读性极高，排查问题很快（比如：前端页面上看到ALIPAY这个类型，一眼就能知道是支付宝）
可以控制不允许数据库的pay_type为空字符串这种情况（因为枚举字段不可能有空字符串）
支持的类型限制死，前端传个其他的字符串无法存入数据库。

枚举用法示例

建表

CREATE TABLE `t_order` (
  `id` bigint NOT NULL COMMENT 'ID',
  `order_no` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '订单号',
  `pay_type` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '支付类型。ALIPAY：支付宝；WECHAT_PAY：微信；BANK_CARD_PAY：银行卡支付。',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='订单';

pay_type字段加了NOT NULL限制。

Entity

package com.example.demo.order.entity;
import com.baomidou.mybatisplus.annotation.TableName;
import com.example.demo.order.enums.PayTypeEnum;
import lombok.Data;
@Data
@TableName("t_order")
public class Order {
    private Long id;
    private String orderNo;
    private PayTypeEnum payType;
}

Enum

package com.example.demo.order.enums;
import lombok.Getter;
@Getter
public enum PayTypeEnum {
    ALIPAY("支付宝"),
    WECHAT_PAY("微信支付"),
    BANK_CARD_PAY("银行卡支付"),
    ;
    private final String description;
    PayTypeEnum(String description) {
        this.description = description;
    }
}

Controller

package com.example.demo.order.controller;
import com.example.demo.order.entity.Order;
import com.example.demo.order.service.OrderService;
import com.example.demo.user.entity.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RestController
@RequestMapping("/order")
public class OrderController {
    @Autowired
    private OrderService orderService;
    @PostMapping("pay")
    public void pay(@RequestBody Order order) {
        orderService.save(order);
    }
}

Service

接口

package com.example.demo.order.service;
import com.baomidou.mybatisplus.extension.service.IService;
import com.example.demo.order.entity.Order;
public interface OrderService extends IService {
}

实现

package com.example.demo.order.service.impl;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.demo.order.entity.Order;
import com.example.demo.order.mapper.OrderMapper;
import com.example.demo.order.service.OrderService;
import org.springframework.stereotype.Service;
@Service
public class OrderServiceImpl extends ServiceImpl implements OrderService {
}

Mapper

package com.example.demo.order.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.order.entity.Order;
import org.springframework.stereotype.Repository;
@Repository
public interface OrderMapper extends BaseMapper {
}

测试

1.正常操作

写入成功，枚举的name()方法的值会写到数据库。

后端结果

数据库结果

2.前端传空字符串

此时会报错，因为枚举中没有对应空字符串的。

后端结果（无法将空字符串反序列化为枚举对象）

2022-09-10 10:14:30.406 WARN 128760 --- [nio-8080-exec-8] .w.s.m.s.DefaultHandlerExceptionResolver : Resolved [org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `com.example.demo.order.enums.PayTypeEnum` from String "": not one of the values accepted for Enum class: [ALIPAY, BANK_CARD_PAY, WECHAT_PAY]; nested exception is com.fasterxml.jackson.databind.exc.InvalidFormatException: Cannot deserialize value of type `com.example.demo.order.enums.PayTypeEnum` from String "": not one of the values accepted for Enum class: [ALIPAY, BANK_CARD_PAY, WECHAT_PAY]
at [Source: (PushbackInputStream); line: 4, column: 16] (through reference chain: com.example.demo.order.entity.Order["payType"])]

数据库结果（没写入数据）

3.前端传null

后端结果（pay_type为null，写入数据库时报错）

2022-09-10 10:24:20.514 ERROR 128760 --- [io-8080-exec-10] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.dao.DataIntegrityViolationException:
### Error updating database. Cause: java.sql.SQLException: Field 'pay_type' doesn't have a default value
### The error may exist in com/example/demo/order/mapper/OrderMapper.java (best guess)
### The error may involve com.example.demo.order.mapper.OrderMapper.insert-Inline
### The error occurred while setting parameters
### SQL: INSERT INTO t_order ( id, order_no ) VALUES ( ?, ? )
### Cause: java.sql.SQLException: Field 'pay_type' doesn't have a default value
; Field 'pay_type' doesn't have a default value; nested exception is java.sql.SQLException: Field 'pay_type' doesn't have a default value] with root cause

java.sql.SQLException: Field 'pay_type' doesn't have a default value
   at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:953) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.mysql.cj.jdbc.ClientPreparedStatement.execute(ClientPreparedStatement.java:370) ~[mysql-connector-java-8.0.25.jar:8.0.25]
   at com.zaxxer.hikari.pool.ProxyPreparedStatement.execute(ProxyPreparedStatement.java:44) ~[HikariCP-3.4.5.jar:na]
......