Twitter的Snowflake 分布式自增长Id生成器

package ext.util;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.util.Date;

/**

• 名称：IdWorker.java 描述：分布式自增涨ID Java实现方案：Twitter的Snowflake 1||0—0000000000

• 0000000000 0000000000 0000000000 0 — 00000 —00000 —000000000000

• 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，

• 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），然后12位该毫秒内的当前毫秒内的计数，

• 加起来刚好64位，为一个Long型。

• 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），

• 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。 64位ID

• (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))

• @author hww
  */
  public class IdWorker {

  // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
  private final static long twepoch = 1545994638225L;
  // 机器标识位数
  private final static long workerIdBits = 5L;
  // 数据中心标识位数
  private final static long datacenterIdBits = 5L;
  // 机器ID最大值
  private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
  // 数据中心ID最大值
  private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
  // 毫秒内自增位
  private final static long sequenceBits = 12L;
  // 机器ID偏左移12位
  private final static long workerIdShift = sequenceBits;
  // 数据中心ID左移17位
  private final static long datacenterIdShift = sequenceBits + workerIdBits;
  // 时间毫秒左移22位
  private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

  private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
  /* 上次生产id时间戳 */
  private static long lastTimestamp = -1L;
  // 0，并发控制
  private long sequence = 0L;

  private final long workerId;
  // 数据标识id部分
  private final long datacenterId;

  public IdWorker() {
  this.datacenterId = getDatacenterId(maxDatacenterId);
  this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
  }

  /**

  @param workerId 工作机器ID
• @param datacenterId 序列号
  */
  public IdWorker(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;
  }

/**

• 获取下一个ID

• @return
  */
  public synchronized long nextId() {
  long timestamp = timeGen();
  if (timestamp < lastTimestamp) {
  throw new RuntimeException(String.format(
  “Clock moved backwards. Refusing to generate id for %d milliseconds”, lastTimestamp - timestamp));
  }

  if (lastTimestamp == timestamp) {
  // 当前毫秒内，则+1
  sequence = (sequence + 1) & sequenceMask;
  if (sequence == 0) {
  // 当前毫秒内计数满了，则等待下一秒
  timestamp = tilNextMillis(lastTimestamp);
  }
  } else {
  sequence = 0L;
  }
  lastTimestamp = timestamp;
  // ID偏移组合生成最终的ID，并返回ID
  long nextId = ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift)
  | (workerId << workerIdShift) | sequence;

  return nextId;
  }

private long tilNextMillis(final long lastTimestamp) {
long timestamp = this.timeGen();
while (timestamp <= lastTimestamp) {
timestamp = this.timeGen();
}
return timestamp;
}

private long timeGen() {
return System.currentTimeMillis();
}

/**

• 获取 maxWorkerId

/
protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
StringBuffer mpid = new StringBuffer();
mpid.append(datacenterId);
String name = ManagementFactory.getRuntimeMXBean().getName();
if (!name.isEmpty()) {
/
* GET jvmPid
/
mpid.append(name.split("@")[0]);
}
/
* MAC + PID 的 hashcode 获取16个低位
*/
return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
}

/**

• 数据标识id部分

*/
protected static long getDatacenterId(long maxDatacenterId) {
long id = 0L;
try {
InetAddress ip = InetAddress.getLocalHost();
NetworkInterface network = NetworkInterface.getByInetAddress(ip);
if (network == null) {
id = 1L;
} else {
byte[] mac = network.getHardwareAddress();
id = ((0x000000FF & (long) mac[mac.length - 1])
| (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
id = id % (maxDatacenterId + 1);
}
} catch (Exception e) {
System.out.println(" getDatacenterId: " + e.getMessage());
}
return id;
}

public static void main(String[] args) {
Date date = new Date();
System.out.println(date.getTime());
IdWorker idWorker = new IdWorker();
System.out.println(“idWorker=” + idWorker.nextId());
IdWorker id = new IdWorker();
for (int i = 0; i < 10; i++) {
long dd = id.nextId();
System.out.println(“dd=” + dd + " === lenth=" + String.valueOf(dd).length());
}
}
}