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package util;import java.lang.management.ManagementFactory;import java.net.InetAddress;import java.net.NetworkInterface;/** * 
名称：IdWorker.java
 * 
描述：分布式自增长ID
 * Twitter的 Snowflake　JAVA实现方案 * 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。 *  * 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();    }    /**     * 
     * 获取 maxWorkerId     * 
     */    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);    }    /**     * 
     * 数据标识id部分     * 
     */    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;    }}

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