主键生成策略

本文参考：http://www.blogjava.net/stevenjohn/archive/2015/05/17/425127.html?utm_source=tuicool

SnowflakeIdHelper.java：

package com.xy6.snowflake;

import java.util.Date;

public final class SnowflakeIdHelper {

	private static long workerId = 0;

	private static long datacenterId = 0;

	private static SnowflakeIdWorker idWorker = new SnowflakeIdWorker(workerId, datacenterId);

	private SnowflakeIdHelper() {
	}

	public static SnowflakeIdWorker getSnowflakeIdWorker() {
		return idWorker;
	}

	public static long generateId() {
		return idWorker.nextId();
	}

	public static String generateStrId() {
		return idWorker.nextId() + "";
	}

	public static long getTimestampValue(long id) {
		long twepoch = SnowflakeIdWorker.twepoch;
		long time = id >> 22;
		return time + twepoch;
	}

	public static Date getTimestamp(long id) {
		return new Date(getTimestampValue(id));
	}

	public static long getGenerateIdStart(Date date) {
		long sequence = 0L;
		long workerIdBits = 5L;
		long datacenterIdBits = 5L;
		long sequenceBits = 12L;

		long workerIdShift = sequenceBits;
		long datacenterIdShift = sequenceBits + workerIdBits;
		long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

		long twepoch = SnowflakeIdWorker.twepoch;
		long timestamp = date.getTime();
		return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
	}

	public static long getDatacenterId() {
		return datacenterId;
	}

	public void setDatacenterId(long datacenterId) {
		SnowflakeIdHelper.datacenterId = datacenterId;
	}

	public static long getWorkerId() {
		return workerId;
	}

	public void setWorkerId(long workerId) {
		SnowflakeIdHelper.workerId = workerId;
	}

	/**
	 * 初始化方法
	 */
	public static void init(long workerId, long datacenterId) {
		SnowflakeIdHelper.workerId = workerId;
		SnowflakeIdHelper.datacenterId = datacenterId;
		idWorker = new SnowflakeIdWorker(workerId, datacenterId);
	}

	/**
	 * 初始化方法
	 */
	public void init() {
		idWorker = new SnowflakeIdWorker(workerId, datacenterId);
	}

}

SnowflakeIdWorker.java：

package com.xy6.snowflake;

import java.util.Random;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class SnowflakeIdWorker {

	protected static final Logger LOG = LoggerFactory.getLogger(SnowflakeIdWorker.class);

	private long workerId;
	private long datacenterId;
	private long sequence = 0L;

	/** 2015-01-01 00:00:00 */
	// public static long twepoch = 1420041600000L;
	public static long twepoch = 1288834974657L;

	private long workerIdBits = 5L;
	private long datacenterIdBits = 5L;
	private long maxWorkerId = -1L ^ (-1L << workerIdBits);
	private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	private long sequenceBits = 12L;

	private long workerIdShift = sequenceBits;
	private long datacenterIdShift = sequenceBits + workerIdBits;
	private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
	private long sequenceMask = -1L ^ (-1L << sequenceBits);

	private long lastTimestamp = -1L;

	private Random r = new Random();

	public SnowflakeIdWorker(long workerId, long datacenterId) {
		// sanity check for workerId
		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;
		LOG.info(String.format("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d", timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId));
	}

	public synchronized long nextId() {
		long timestamp = timeGen();

		if (timestamp < lastTimestamp) {
			LOG.error(String.format("clock is moving backwards.  Rejecting requests until %d.", lastTimestamp));
			throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
		}

		if (lastTimestamp == timestamp) {
			sequence = (sequence + 1) & sequenceMask;
			if (sequence == 0) {
				timestamp = tilNextMillis(lastTimestamp);
			}
		} else {
			// sequence = 0L;
			sequence = r.nextInt(2);
		}

		lastTimestamp = timestamp;

		return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
	}

	protected long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

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

用法：

package com.xy6.snowflake;

public class Demo2 {

	public static void main(String[] args) {
		// 716908940310347777
		System.err.println(SnowflakeIdHelper.generateId());
	}

}