content: package com.java2nb.common.utils;
  
  
  import java.lang.management.ManagementFactory;
  import java.net.InetAddress;
  import java.net.NetworkInterface;
  
  /**
   * <p>名称：IdWorker.java</p>
   * <p>描述：分布式自增长ID</p>
   * <pre>
   *     Twitter的 Snowflake　JAVA实现方案
   * </pre>
   * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用：
   * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
   * 在上面的字符串中，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。
   * 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），
   * 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。
   * <p>
   * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
   *
   */
  public class IdWorker {
      // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
      private final static long twepoch = 1288834974657L;
      // 机器标识位数
      private final static long workerIdBits = 5L;
      // 数据中心标识位数
      private final static long datacenterIdBits = 5L;
      // 机器ID最大值
      private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
      // 数据中心ID最大值
      private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
      // 毫秒内自增位
      private final static long sequenceBits = 12L;
      // 机器ID偏左移12位
      private final static long workerIdShift = sequenceBits;
      // 数据中心ID左移17位
      private final static long datacenterIdShift = sequenceBits + workerIdBits;
      // 时间毫秒左移22位
      private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
  
      private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
      /* 上次生产id时间戳 */
      private static long lastTimestamp = -1L;
      // 0，并发控制
      private long sequence = 0L;
  
      private final long workerId;
      // 数据标识id部分
      private final long datacenterId;
  
      public IdWorker(){
          this.datacenterId = getDatacenterId(maxDatacenterId);
          this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
      }
      /**
       * @param workerId
       *            工作机器ID
       * @param datacenterId
       *            序列号
       */
      public IdWorker(long workerId, long datacenterId) {
          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;
      }
      /**
       * 获取下一个ID
       *
       * @return
       */
      public synchronized long nextId() {
          long timestamp = timeGen();
          if (timestamp < lastTimestamp) {
              throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
          }
  
          if (lastTimestamp == timestamp) {
              // 当前毫秒内，则+1
              sequence = (sequence + 1) & sequenceMask;
              if (sequence == 0) {
                  // 当前毫秒内计数满了，则等待下一秒
                  timestamp = tilNextMillis(lastTimestamp);
              }
          } else {
              sequence = 0L;
          }
          lastTimestamp = timestamp;
          // ID偏移组合生成最终的ID，并返回ID
          long nextId = ((timestamp - twepoch) << timestampLeftShift)
                  | (datacenterId << datacenterIdShift)
                  | (workerId << workerIdShift) | sequence;
  
          return nextId;
      }
  
      private long tilNextMillis(final long lastTimestamp) {
          long timestamp = this.timeGen();
          while (timestamp <= lastTimestamp) {
              timestamp = this.timeGen();
          }
          return timestamp;
      }
  
      private long timeGen() {
          return System.currentTimeMillis();
      }
  
      /**
       * <p>
       * 获取 maxWorkerId
       * </p>
       */
      protected static long getMaxWorkerId(long datacenterId, long maxWorkerId) {
          StringBuffer mpid = new StringBuffer();
          mpid.append(datacenterId);
          String name = ManagementFactory.getRuntimeMXBean().getName();
          if (!name.isEmpty()) {
              /*
               * GET jvmPid
               */
              mpid.append(name.split("@")[0]);
          }
          /*
           * MAC + PID 的 hashcode 获取16个低位
           */
          return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
      }
  
      /**
       * <p>
       * 数据标识id部分
       * </p>
       */
      protected static long getDatacenterId(long maxDatacenterId) {
          long id = 0L;
          try {
              InetAddress ip = InetAddress.getLocalHost();
              NetworkInterface network = NetworkInterface.getByInetAddress(ip);
              if (network == null) {
                  id = 1L;
              } else {
                  byte[] mac = network.getHardwareAddress();
                  id = ((0x000000FF & (long) mac[mac.length - 1])
                          | (0x0000FF00 & (((long) mac[mac.length - 2]) << 8))) >> 6;
                  id = id % (maxDatacenterId + 1);
              }
          } catch (Exception e) {
              System.out.println(" getDatacenterId: " + e.getMessage());
          }
          return id;
      }
  
  
  }
  