content: package com.wenmrong.community1.community.utils;
  
  /**
   * 描述: Twitter的分布式自增ID雪花算法snowflake (Java版)
   *
   * @author yanpenglei
   * @create 2018-03-13 12:37
   **/
  public class SnowFlake {
   
      /**
       * 起始的时间戳
       */
      private final static long START_STMP = 1480166465631L;
   
      /**
       * 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;  //数据中心
      private long machineId;     //机器标识
      private long sequence = 0L; //序列号
      private long lastStmp = -1L;//上一次时间戳
   
      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();
      }
   
  
  }