前后端交互Long类型映射为number类型精度丢失问题

§解决前后端交互Long类型精度丢失问题

§1. 现象及原因：

在做一个SpringBoot项目，后端使用了雪花算法生成Long类型id，在前端（typescript）映射则为number类型，但是发生了精度丢失导致根据id的查询和删除发生失败。

• 数据库中：

  

• 后端发出：

  

• 前端取得：

  

  §2. 解决方法

  §2.1 将后端的Long类型手动改为String（所有赋值都要改，极不推荐）

  §2.2 加单个注解（需要对多张表的Long id都要加上该注解，不推荐）

  @JsonSerialize(using= ToStringSerializer.class)
  private Long id;
  

  §2.3 添加配置类JacksonConfig.java

  import com.fasterxml.jackson.databind.ObjectMapper;
  import com.fasterxml.jackson.databind.module.SimpleModule;
  import com.fasterxml.jackson.databind.ser.std.ToStringSerializer;
  import org.springframework.context.annotation.Bean;
  import org.springframework.context.annotation.Configuration;
  import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
  
  /**
   * 统一注解，解决前后端交互Long类型精度丢失的问题
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   */
  @Configuration
  public class JacksonConfig {
      @Bean
      public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
          ObjectMapper objectMapper = builder.createXmlMapper(false).build();
          SimpleModule simpleModule = new SimpleModule();
          simpleModule.addSerializer(Long.class, ToStringSerializer.instance);
          objectMapper.registerModule(simpleModule);
          return objectMapper;
      }
  }
  

  §3. 附雪花算法的java版本-SnowFlake.java工具类

  package com.whalelan.wiki.utils;
  
  import org.springframework.stereotype.Component;
  
  import java.text.ParseException;
  import java.text.SimpleDateFormat;
  import java.util.Date;
  
  /**
   * Twitter的分布式自增ID雪花算法（时间戳+一些机器码+递增的序列号）
   **/
  @Component
  public class SnowFlake {
  
      /**
       * 起始的时间戳
       */
      private final static long START_STMP = 1609459200000L; // 2021-01-01 00:00:00
  
      /**
       * 每一部分占用的位数
       */
      private final static long SEQUENCE_BIT = 12; //序列号占用的位数
      private final static long MACHINE_BIT = 5;   //机器标识占用的位数
      private final static long DATACENTER_BIT = 5;//数据中心占用的位数
  
      /**
       * 每一部分的最大值
       */
      private final static long MAX_DATACENTER_NUM = -1L ^ (-1L << DATACENTER_BIT);
      private final static long MAX_MACHINE_NUM = -1L ^ (-1L << MACHINE_BIT);
      private final static long MAX_SEQUENCE = -1L ^ (-1L << SEQUENCE_BIT);
  
      /**
       * 每一部分向左的位移
       */
      private final static long MACHINE_LEFT = SEQUENCE_BIT;
      private final static long DATACENTER_LEFT = SEQUENCE_BIT + MACHINE_BIT;
      private final static long TIMESTMP_LEFT = DATACENTER_LEFT + DATACENTER_BIT;
  
      private long datacenterId = 1;  //数据中心
      private long machineId = 1;     //机器标识
      private long sequence = 0L; //序列号
      private long lastStmp = -1L;//上一次时间戳
  
      public SnowFlake() {
      }
  
      public SnowFlake(long datacenterId, long machineId) {
          if (datacenterId > MAX_DATACENTER_NUM || datacenterId < 0) {
              throw new IllegalArgumentException("datacenterId can't be greater than MAX_DATACENTER_NUM or less than 0");
          }
          if (machineId > MAX_MACHINE_NUM || machineId < 0) {
              throw new IllegalArgumentException("machineId can't be greater than MAX_MACHINE_NUM or less than 0");
          }
          this.datacenterId = datacenterId;
          this.machineId = machineId;
      }
  
      /**
       * 产生下一个ID
       *
       * @return
       */
      public synchronized long nextId() {
          long currStmp = getNewstmp();
          if (currStmp < lastStmp) {
              throw new RuntimeException("Clock moved backwards.  Refusing to generate id");
          }
  
          if (currStmp == lastStmp) {
              //相同毫秒内，序列号自增
              sequence = (sequence + 1) & MAX_SEQUENCE;
              //同一毫秒的序列数已经达到最大
              if (sequence == 0L) {
                  currStmp = getNextMill();
              }
          } else {
              //不同毫秒内，序列号置为0
              sequence = 0L;
          }
  
          lastStmp = currStmp;
  
          return (currStmp - START_STMP) << TIMESTMP_LEFT //时间戳部分
                  | datacenterId << DATACENTER_LEFT       //数据中心部分
                  | machineId << MACHINE_LEFT             //机器标识部分
                  | sequence;                             //序列号部分
      }
  
      private long getNextMill() {
          long mill = getNewstmp();
          while (mill <= lastStmp) {
              mill = getNewstmp();
          }
          return mill;
      }
  
      private long getNewstmp() {
          return System.currentTimeMillis();
      }
  
      public static void main(String[] args) throws ParseException {
          // 时间戳
          // System.out.println(System.currentTimeMillis());
          // // System.out.println("爱老虎油");
          //
          // System.out.println(new Date().getTime());
          //
          // // String dateTime = "1970-01-01 08:00:00";  //时间戳0点
          // String dateTime = "2021-01-01 08:00:00";
          // SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
          // System.out.println(sdf.parse(dateTime).getTime());
  
          //雪花算法生成雪花ID示例
          SnowFlake snowFlake = new SnowFlake(1, 1);
  
          long start = System.currentTimeMillis();
          for (int i = 0; i < 10; i++) {
              System.out.println(snowFlake.nextId());
              //生成所耗用的时间
              System.out.println(System.currentTimeMillis() - start);
          }
      }
  }
  
  

方法来源

• 推荐视频课程：《Spring Boot + Vue3 前后端分离 实战wiki知识库系统》