package com; public class SnowflakeIdGenerator {  //================================================Algorithm's Parameter=============================================  // 體系開端時刻截 (UTC 2017-06-28 00:00:00)  private final long startTime = 1498608000000L;  // 機器id所占的位數(shù)  private final long workerIdBits = 5L;  // 數(shù)據(jù)標識id所占的位數(shù)  private final long dataCenterIdBits = 5L;  // 支撐的最大機器id(十進制)，結(jié)果是31 (這個移位算法能夠很快的計算出幾位二進制數(shù)所能表明的最大十進制數(shù))  // -1L 左移 5位 (worker id 所占位數(shù)) 即 5位二進制所能取得的最大十進制數(shù) - 31  private final long maxWorkerId = -1L ^ (-1L << workerIdBits);  // 支撐的最大數(shù)據(jù)標識id - 31  private final long maxDataCenterId = -1L ^ (-1L << dataCenterIdBits);  // 序列在id中占的位數(shù)  private final long sequenceBits = 12L;  // 機器ID 左移位數(shù) - 12 (即末 sequence 所占用的位數(shù))  private final long workerIdMoveBits = sequenceBits;  // 數(shù)據(jù)標識id 左移位數(shù) - 17(12+5)  private final long dataCenterIdMoveBits = sequenceBits + workerIdBits;  // 時刻截向 左移位數(shù) - 22(5+5+12)  private final long timestampMoveBits = sequenceBits + workerIdBits + dataCenterIdBits;  // 生成序列的掩碼(12位所對應(yīng)的最大整數(shù)值)，這兒為4095 (0b111111111111=0xfff=4095)  private final long sequenceMask = -1L ^ (-1L << sequenceBits);  //=================================================Works's Parameter================================================  /**  * 作業(yè)機器ID(0~31)  */  private long workerId;  /**  * 數(shù)據(jù)中心ID(0~31)  */  private long dataCenterId;  /**  * 毫秒內(nèi)序列(0~4095)  */  private long sequence = 0L;  /**  * 前次生成ID的時刻截  */  private long lastTimestamp = -1L;  //===============================================Constructors=======================================================  /**  * 構(gòu)造函數(shù)  *  * @param workerId     作業(yè)ID (0~31)  * @param dataCenterId 數(shù)據(jù)中心ID (0~31)  */  public SnowflakeIdGenerator(long workerId, long dataCenterId) {  if (workerId > maxWorkerId || workerId < 0) {  throw new IllegalArgumentException(String.format("Worker Id can't be greater than %d or less than 0", maxWorkerId));  }  if (dataCenterId > maxDataCenterId || dataCenterId < 0) {  throw new IllegalArgumentException(String.format("DataCenter Id can't be greater than %d or less than 0", maxDataCenterId));  }  this.workerId = workerId;  this.dataCenterId = dataCenterId;  }  // ==================================================Methods========================================================  // 線程安全的取得下一個 ID 的辦法  public synchronized long nextId() {  long timestamp = currentTime();  //假如當(dāng)時時刻小于上一次ID生成的時刻戳: 闡明體系時鐘回退過 - 這個時候應(yīng)當(dāng)拋出反常  if (timestamp < lastTimestamp) {  throw new RuntimeException(  String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));  }  //假如是同一時刻生成的，則進行毫秒內(nèi)序列  if (lastTimestamp == timestamp) {  sequence = (sequence + 1) & sequenceMask;  //毫秒內(nèi)序列溢出 即 序列 > 4095  if (sequence == 0) {  //阻塞到下一個毫秒,取得新的時刻戳  timestamp = blockTillNextMillis(lastTimestamp);  }  }  //時刻戳改動，毫秒內(nèi)序列重置  else {  sequence = 0L;  }  //前次生成ID的時刻截  lastTimestamp = timestamp;  //移位并經(jīng)過或運算拼到一起組成64位的ID  return ((timestamp - startTime) << timestampMoveBits) //  | (dataCenterId << dataCenterIdMoveBits) //  | (workerId << workerIdMoveBits) //  | sequence;  }  // 阻塞到下一個毫秒 即 直到取得新的時刻戳  protected long blockTillNextMillis(long lastTimestamp) {  long timestamp = currentTime();  while (timestamp <= lastTimestamp) {  timestamp = currentTime();  }  return timestamp;  }  // 取得以毫秒為單位的當(dāng)時時刻  protected long currentTime() {  return System.currentTimeMillis();  }  //====================================================Test Case=====================================================  public static void main(String[] args) {  SnowflakeIdGenerator idWorker = new SnowflakeIdGenerator(0, 0);  for (int i = 0; i < 100; i++) {  long id = idWorker.nextId();  //System.out.println(Long.toBinaryString(id));  System.out.println(id);  }  } }