Snowflake ID, distributed unique ID

 /**
 * <p> name ：IdWorker.java</p>
 * <p> describe ： Distributed self growth ID</p>
 * <pre>
 *     Twitter Of Snowflake　JAVA Implementation scheme
 * </pre>
 * The core code is IdWorker This class implementation , Its principle and structure are as follows , I use one for each 0 It means one person , use — The function of dividing parts ：
 * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
 * In the string above , The first is unused （ In fact, it can also be used as long The sign bit of ）, Next 41 Bit is millisecond time ,
 * then 5 position datacenter Identification bit ,5 Bit machine ID（ It's not an identifier , It's actually identifying the thread ）,
 * then 12 The count of the current millisecond in that millisecond , It just adds up to 64 position , For one Long type .
 * The advantage of this is , On the whole, it is sorted according to the increasing time , And the whole distributed system will not produce ID Collision （ from datacenter And machines ID Make a distinction ）,
 * And it's more efficient , After testing ,snowflake Every second can produce 26 ten thousand ID about , Fully meet the needs .
 * <p>
 * 64 position ID (42( millisecond )+5( machine ID)+5( Business coding )+12( Add up again and again ))
 *
 */

package com.rabee.common.utils.uuid;
import org.springframework.stereotype.Component;

import java.lang.management.ManagementFactory;
import java.net.InetAddress;
import java.net.NetworkInterface;

@Component
public class SnowflakeIdUtil {
    /**
     *   Time start mark point , As a benchmark , Generally, the latest time of the system （ Once it is determined that it cannot be changed ）
     */
    private final static long twepoch = 1420041600000L;
    /**
     *   Number of machine marks 
     */
    private final static long workerIdBits = 5L;
    /**
     *  Data center identification number 
     */
    private final static long datacenterIdBits = 5L;
    /**
     *  machine ID Maximum 
     */
    private final static long maxWorkerId = -1L ^ (-1L << workerIdBits);
    /**
     *  Data Center ID Maximum 
     */
    private final static long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    /**
     *  Auto increment in milliseconds 
     */
    private final static long sequenceBits = 12L;
    /**
     *  machine ID Shift to the left 12 position 
     */
    private final static long workerIdShift = sequenceBits;
    /**
     *  Data Center ID Move left 17 position 
     */
    private final static long datacenterIdShift = sequenceBits + workerIdBits;
    /**
     *  Time millisecond shift left 22 position 
     */
    private final static long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;

    private final static long sequenceMask = -1L ^ (-1L << sequenceBits);
    /**
     *  Last production id Time stamp 
     */
    private static long lastTimestamp = -1L;
    /**
     *  concurrency control 
     */
    private long sequence = 0L;

    private final long workerId;
    /**
     *  Data identification id part 
     */
    private final long datacenterId;

    public SnowflakeIdUtil(){
        this.datacenterId = getDatacenterId(maxDatacenterId);
        this.workerId = getMaxWorkerId(datacenterId, maxWorkerId);
    }
    /**
     * @param workerId
     *             Work the machine ID
     * @param datacenterId
     *             Serial number 
     */
    public SnowflakeIdUtil(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;
    }
    /**
     *  Get the next one 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) {
            //  In the current millisecond , be +1
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                //  The current millisecond count is full , The next second 
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }
        lastTimestamp = timestamp;
        // ID The offset combination generates the final ID, And back to 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>
     *  obtain  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  Of  hashcode  obtain 16 Low position 
         */
        return (mpid.toString().hashCode() & 0xffff) % (maxWorkerId + 1);
    }

    /**
     * <p>
     *  Data identification id part 
     * </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) {
        SnowflakeIdUtil sf  = new SnowflakeIdUtil();
        String id  =String.valueOf(sf.nextId());
        System.out.println(""+id+":"+id.length());
    }

}