分布式的Id生成器
项目中需要一个分布式的Id生成器,twitter的Snowflake中这个既简单又高效,网上找的Java版本
package com.cqfc.id; import org.slf4j.Logger; import org.slf4j.LoggerFactory; /** * tweeter的snowflake 移植到Java: * (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 = this.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(1); 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 = this.timeGen(); while (timestamp <= lastTimestamp) { timestamp = this.timeGen(); } return timestamp; } /** * 获得系统当前毫秒数 */ private static long timeGen() { return System.currentTimeMillis(); } public static void main(String[] args) throws Exception { System.out.println(timeGen()); IdWorker idWorker = IdWorker.getFlowIdWorkerInstance(); // System.out.println(Long.toBinaryString(idWorker.nextId())); System.out.println(idWorker.nextId()); System.out.println(idWorker.nextId()); } }