技术汇总：第六章：分布式自增长ID

package util;

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))  *  * @author Polim  */ 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;     }

    public static void main(String[] args) {         IdWorker idWorker=new IdWorker(0,0);         for(int i=0;i<100;i ){             long nextId = idWorker.nextId();             System.out.println(nextId);         }     }

}