/// /// 根据twitter的snowflake算法生成唯一ID /// snowflake算法 64 位 /// 0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000 /// 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。 /// 其中datacenter标识位起始是机器位，机器ID其实是线程标识，可以同一一个10位来表示不同机器 /// public class IdWorker { //机器ID private static long workerId = 1; private static long twepoch = 687888001020L; //唯一时间，这是一个避免重复的随机量，自行设定不要大于当前时间戳 private static long sequence = 0L; private static int workerIdBits = 4; //机器码字节数。4个字节用来保存机器码 public static long maxWorkerId = -1L ^ -1L << workerIdBits; //最大机器ID private static int sequenceBits = 10; //计数器字节数，10个字节用来保存计数码 private static int workerIdShift = sequenceBits; //机器码数据左移位数，就是后面计数器占用的位数 private static int timestampLeftShift = sequenceBits + workerIdBits; //时间戳左移动位数就是机器码和计数器总字节数 public static long sequenceMask = -1L ^ -1L << sequenceBits; //一微秒内可以产生计数，如果达到该值则等到下一微妙在进行生成 private long lastTimestamp = -1L; public long nextId() { lock (this) { long timestamp = timeGen(); if (this.lastTimestamp == timestamp) { //同一微妙中生成ID IdWorker.sequence = (IdWorker.sequence + 1) & IdWorker.sequenceMask; //用&运算计算该微秒内产生的计数是否已经到达上限 if (IdWorker.sequence == 0) { //一微妙内产生的ID计数已达上限，等待下一微妙 timestamp = tillNextMillis(this.lastTimestamp); } } else { //不同微秒生成ID IdWorker.sequence = 0; //计数清0 } if (timestamp < lastTimestamp) { //如果当前时间戳比上一次生成ID时时间戳还小，抛出异常，因为不能保证现在生成的ID之前没有生成过 throw new Exception(string.Format("Clock moved backwards. Refusing to generate id for {0} milliseconds", this.lastTimestamp - timestamp)); } this.lastTimestamp = timestamp; //把当前时间戳保存为最后生成ID的时间戳 long nextId = (timestamp - twepoch << timestampLeftShift) | IdWorker.workerId << IdWorker.workerIdShift | IdWorker.sequence; return nextId; } } /// /// 获取下一微秒时间戳 /// /// /// private long tillNextMillis(long lastTimestamp) { long timestamp = timeGen(); while (timestamp <= lastTimestamp) { timestamp = timeGen(); } return timestamp; } /// /// 生成当前时间戳 /// /// private long timeGen() { return (long)(DateTime.UtcNow - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds; } }
import org.slf4j.Logger;import org.slf4j.LoggerFactory;import org.springframework.stereotype.Component;public class IdWorker { protected static final Logger LOG = LoggerFactory.getLogger(IdWorker.class); private long workerId; private long datacenterId; private long sequence = 0L; private 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; public IdWorker(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; } 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(); }}