IdWorker

package com.rrjc.pf.common;
	import java.net.InetAddress;
	import org.slf4j.Logger;
	import org.slf4j.LoggerFactory;
	/**
	* (a) id构成: 42位的时间前缀 + 10位的节点标识 + 12位的sequence避免并发的数字(12位不够用时强制得到新的时间前缀)
	* 注意这里进行了小改动: snowkflake是5位的datacenter加5位的机器id; 这里变成使用10位的机器id
	* (b) 对系统时间的依赖性非常强，需关闭ntp的时间同步功能。当检测到ntp时间调整后，将会拒绝分配id
	*/
	public class IdWorker {
	private final static Logger logger = LoggerFactory.getLogger(IdWorker.class);
	private final long workerId;
	private final long epoch = 1403854494756L; // 时间起始标记点，作为基准，一般取系统的最近时间
	private final long workerIdBits = 10L; // 机器标识位数
	private final long maxWorkerId = -1L ^ -1L << this.workerIdBits;// 机器ID最大值: 1023
	private long sequence = 0L; // 0，并发控制
	private final long sequenceBits = 12L; //毫秒内自增位
	private final long workerIdShift = this.sequenceBits; // 12
	private final long timestampLeftShift = this.sequenceBits + this.workerIdBits;// 22
	private final long sequenceMask = -1L ^ -1L << this.sequenceBits; // 4095,111111111111,12位
	private long lastTimestamp = -1L;
	private IdWorker(long workerId) {
	if (workerId > this.maxWorkerId || workerId < 0) {
	throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", this.maxWorkerId));
	}
	this.workerId = workerId;
	}
	public synchronized long nextId() throws Exception {
	long timestamp = IdWorker.timeGen();
	if (this.lastTimestamp == timestamp) { // 如果上一个timestamp与新产生的相等，则sequence加一(0-4095循环); 对新的timestamp，sequence从0开始
	this.sequence = this.sequence + 1 & this.sequenceMask;
	if (this.sequence == 0) {
	timestamp = this.tilNextMillis(this.lastTimestamp);// 重新生成timestamp
	}
	} else {
	this.sequence = 0;
	}
	if (timestamp < this.lastTimestamp) {
	logger.error(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
	throw new Exception(String.format("clock moved backwards.Refusing to generate id for %d milliseconds", (this.lastTimestamp - timestamp)));
	}
	this.lastTimestamp = timestamp;
	return timestamp - this.epoch << this.timestampLeftShift | this.workerId << this.workerIdShift | this.sequence;
	}
	private static IdWorker flowIdWorker = new IdWorker(getworkerHostIp());
	public static IdWorker getFlowIdWorkerInstance() {
	return flowIdWorker;
	}
	/**
	* 等待下一个毫秒的到来, 保证返回的毫秒数在参数lastTimestamp之后
	*/
	private long tilNextMillis(long lastTimestamp) {
	long timestamp = IdWorker.timeGen();
	while (timestamp <= lastTimestamp) {
	timestamp = IdWorker.timeGen();
	}
	return timestamp;
	}
	/**
	* 获得系统当前毫秒数
	*/
	private static long timeGen() {
	return System.currentTimeMillis();
	}
	/**
	*
	* @param bytes
	* @return int
	*/
	public static int getworkerHostIp() {
	try {
	byte[] bytes = InetAddress.getLocalHost().getAddress();
	return Integer.valueOf(bytes[3] & 0xFF);
	} catch (Exception e) {
	logger.error(e.getMessage(),e);
	return 1;
	}
	}
	public static void main(String[] args) throws Exception {
	IdWorker idWorker = IdWorker.getFlowIdWorkerInstance();
	System.out.println(idWorker.nextId());
	System.out.println(idWorker.nextId());
	}
	}   源地址：https://gist.github.com/xishuixixia/f0f8684805d0504289b7a40f3b327dd6