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import java.net.InetAddress; import java.net.UnknownHostException; import java.text.SimpleDateFormat; public enum IdGenerator { INSTANCE; private long workerId; //用ip地址最后几个字节标示 private long datacenterId = 0L; //可配置在properties中,启动时加载,此处默认先写成0 private long sequence = 0L; private long workerIdBits = 8L; //节点ID长度 private long sequenceBits = 12L; //序列号12位 private long workerIdShift = sequenceBits; //机器节点左移12位 private long datacenterIdShift = sequenceBits + workerIdBits; //数据中心节点左移14位 private long sequenceMask = ~(-1L << sequenceBits); //4095 private long lastTimestamp = -1L; IdGenerator() { workerId = 0x000000FF & getLastIP(); } public synchronized String nextId() { long timestamp = timeGen(); //获取当前毫秒数 //如果服务器时间有问题(时钟后退) 报错。 if (timestamp < lastTimestamp) { throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp)); } //如果上次生成时间和当前时间相同,在同一毫秒内 if (lastTimestamp == timestamp) { //sequence自增，因为sequence只有12bit，所以和sequenceMask相与一下，去掉高位 sequence = (sequence + 1) & sequenceMask; //判断是否溢出,也就是每毫秒内超过4095，当为4096时，与sequenceMask相与，sequence就等于0 if (sequence == 0) { timestamp = tilNextMillis(lastTimestamp); //自旋等待到下一毫秒 } } else { sequence = 0L; //如果和上次生成时间不同,重置sequence，就是下一毫秒开始，sequence计数重新从0开始累加 } lastTimestamp = timestamp; long suffix = (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence; SimpleDateFormat sd = new SimpleDateFormat("yyyyMMddHHMMssSSS"); String datePrefix = sd.format(timestamp); return datePrefix + suffix; } protected long tilNextMillis(long lastTimestamp) { long timestamp = timeGen(); while (timestamp <= lastTimestamp) { timestamp = timeGen(); } return timestamp; } protected long timeGen() { return System.currentTimeMillis(); } private byte getLastIP() { byte lastip = 0; try { InetAddress ip = InetAddress.getLocalHost(); byte[] ipByte = ip.getAddress(); lastip = ipByte[ipByte.length - 1]; } catch (UnknownHostException e) { e.printStackTrace(); } return lastip; } } |
测试
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import org.junit.Assert; import org.junit.Test; import java.util.Collection; import java.util.Collections; import java.util.HashSet; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.TimeUnit; public class IdGeneratorTest { @Test public void nextId() throws Exception { final IdGenerator idg = IdGenerator.INSTANCE; ExecutorService es = Executors.newFixedThreadPool(10); final HashSet idSet = new HashSet<String>(); Collection collection = Collections.synchronizedCollection(idSet); long start = System.currentTimeMillis(); System.out.println("***** start generate id ******"); for (int i = 0; i < 10; i++) es.execute(() -> { for (int j = 0; j < 100000; j++) { String id = idg.nextId(); synchronized (idSet) { idSet.add(id); } } }); es.shutdown(); es.awaitTermination(10, TimeUnit.SECONDS); long end = System.currentTimeMillis(); System.out.println("***** end generate id *****"); System.out.println("***** cost " + (end - start) + " ms!"); Assert.assertEquals(10 * 100000, idSet.size()); //idSet.forEach(o -> System.out.println(o)); } } |
经测试，在1000000次的生成中未出现重复！！
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