雪花算法生成器

雪花算法

package com.ccb.utils;

public class SnowflakeIdGenerator {
    
    
  
  // 定义雪花 ID 的各部分位数
  private static final long TIMESTAMP_BITS = 41L;
  private static final long NODE_ID_BITS = 10L;
  private static final long SEQUENCE_BITS = 12L;

  // 定义起始时间戳（可根据实际情况调整）
  private static final long EPOCH = 1609459200000L;

  // 定义最大取值范围
  private static final long MAX_NODE_ID = (1L << NODE_ID_BITS) - 1;
  private static final long MAX_SEQUENCE = (1L << SEQUENCE_BITS) - 1;

  // 定义偏移量
  private static final long TIMESTAMP_SHIFT = NODE_ID_BITS + SEQUENCE_BITS;
  private static final long NODE_ID_SHIFT = SEQUENCE_BITS;

  private final long nodeId;
  private long lastTimestamp = -1L;
  private long sequence = 0L;

  public SnowflakeIdGenerator(long nodeId) {
    
    
    if (nodeId < 0 || nodeId > MAX_NODE_ID) {
    
    
      throw new IllegalArgumentException("Invalid node ID");
    }
    this.nodeId = nodeId;
  }

  public synchronized long generateId() {
    
    
    long currentTimestamp = timestamp();
    if (currentTimestamp < lastTimestamp) {
    
    
        throw new IllegalStateException("Clock moved backwards");
    }
    if (currentTimestamp == lastTimestamp) {
    
    
      sequence = (sequence + 1) & MAX_SEQUENCE;
      if (sequence == 0) {
    
    
        currentTimestamp = untilNextMillis(lastTimestamp);
      }
    } else {
    
    
      sequence = 0L;
    }
    lastTimestamp = currentTimestamp;
    return ((currentTimestamp - EPOCH) << TIMESTAMP_SHIFT) |
           (nodeId << NODE_ID_SHIFT) |
           sequence;
  }

  private long timestamp() {
    
    
    return System.currentTimeMillis();
  }

  private long untilNextMillis(long lastTimestamp) {
    
    
    long currentTimestamp = timestamp();
    while (currentTimestamp <= lastTimestamp) {
    
    
      currentTimestamp = timestamp();
    }
    return currentTimestamp;
  }

  public static void main(String[] args) {
    
    
    // 创建一个雪花 ID 生成器实例，传入节点 ID
    SnowflakeIdGenerator idGenerator = new SnowflakeIdGenerator(1);
    // 生成 ID
    long id = idGenerator.generateId();
    System.out.println(id);
  }
}