Java 通过手写分布式雪花SnowFlake生成ID方法详解_java

  import java.util.HashSet;  import java.util.concurrent.atomic.AtomicLong;    public class SnowFlake {        //时间 41位      private static long lastTime = System.currentTimeMillis();        //数据中心ID 5位(默认0-31)      private long datacenterId = 0;      private long datacenterIdShift = 5;        //机房机器ID 5位(默认0-31)      private long workerId = 0;      private long workerIdShift = 5;        //随机数 12位(默认0~4095)      private AtomicLong random = new AtomicLong();      private long randomShift = 12;      //随机数的最大值      private long maxRandom = (long) Math.pow(2, randomShift);        public SnowFlake() {      }        public SnowFlake(long workerIdShift, long datacenterIdShift){          if (workerIdShift < 0 ||                  datacenterIdShift < 0 ||                  workerIdShift + datacenterIdShift > 22) {              throw new IllegalArgumentException("参数不匹配");          }          this.workerIdShift = workerIdShift;          this.datacenterIdShift = datacenterIdShift;          this.randomShift = 22 - datacenterIdShift - workerIdShift;          this.maxRandom = (long) Math.pow(2, randomShift);      }        //获取雪花的ID      private long getId() {          return lastTime << (workerIdShift + datacenterIdShift + randomShift) |                  workerId << (datacenterIdShift + randomShift) |                  datacenterId << randomShift |                  random.get();      }        //生成一个新的ID      public synchronized long nextId() {          long now = System.currentTimeMillis();            //如果当前时间和上一次时间不在同一毫秒内，直接返回          if (now > lastTime) {              lastTime = now;              random.set(0);              return getId();          }    	//将最后的随机数，进行+1操作          if (random.incrementAndGet() < maxRandom) {              return getId();          }            //自选等待下一毫秒          while (now <= lastTime) {              now = System.currentTimeMillis();          }            lastTime = now;          random.set(0);          return getId();        }        //测试      public static void main(String[] args) {          SnowFlake snowFlake = new SnowFlake();          HashSet<Long> set = new HashSet<>();          for (int i = 0; i < 10000; i++) {              set.add(snowFlake.nextId());          }          System.out.println(set.size());      }    }