主鍵-雪花算法

package com.test.domi.aspect;

/**
 * 基於Twitter的Snowflake算法實現分布式高效有序ID生產黑科技(sequence) SnowFlake的結構如下(每部分用-分開):<br>
 * 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - * 000000000000 <br>
 * 1位標識，由於long基本類型在Java中是帶符號的，最高位是符號位，正數是0，負數是1，所以id一般是正數，最高位是0<br>
 * 41位時間截(毫秒級)，注意，41位時間截不是存儲當前時間的時間截，而是存儲時間截的差值（當前時間截 - 開始時間截) 得到的值）<br>
 * 這里的的開始時間截，一般是我們的id生成器開始使用的時間，由我們程序來指定的（如下下面程序IdWorker類的startTime屬性）。41位的時間截，可以使用69年<br>
 * 年T = (1L << 41) / (1000L * 60 * 60 * 24 * 365) = 69<br>
 * 10位的數據機器位，可以部署在1024個節點，包括5位datacenterId和5位workerId<br>
 * 12位序列，毫秒內的計數，12位的計數順序號支持每個節點每毫秒(同一機器，同一時間截)產生4096個ID序號<br>
 * 加起來剛好64位，為一個Long型。<br>
 * SnowFlake的優點是，整體上按照時間自增排序，並且整個分布式系統內不會產生ID碰撞(由數據中心ID和機器ID作區分)，並且效率較高，經測試，SnowFlake每秒能夠產生26萬ID左右。
 *
 * @author dxw
 */
public class Sequence {

    /** 開始時間截 */
    private final long twepoch = 1288834974657L;
    /** 機器id所占的位數 */
    private final long workerIdBits = 5L;
    /** 數據標識id所占的位數 */
    private final long datacenterIdBits = 5L;
    /** 支持的最大機器id，結果是31 (這個移位算法可以很快的計算出幾位二進制數所能表示的最大十進制數) */
    private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
    /** 支持的最大數據標識id，結果是31 */
    private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
    /** 序列在id中占的位數 */
    private final long sequenceBits = 12L;
    /** 機器ID向左移12位 */
    private final long workerIdShift = sequenceBits;
    /** 數據標識id向左移17位(12+5) */
    private final long datacenterIdShift = sequenceBits + workerIdBits;
    /** 時間截向左移22位(5+5+12) */
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    /** 生成序列的掩碼，這里為4095 (0b111111111111=0xfff=4095) */
    private final long sequenceMask = -1L ^ (-1L << sequenceBits);

    /** 工作機器ID(0~31) */
    private long workerId;
    /** 數據中心ID(0~31) */
    private long datacenterId;
    /** 毫秒內序列(0~4095) */
    private long sequence = 0L;
    /** 上次生成ID的時間截 */
    private long lastTimestamp = -1L;

    /**
     * @param workerId 工作ID (0~31)
     * @param datacenterId 數據中心ID (0~31)
     */
    public Sequence(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;
    }

    /**
     * 獲得下一個ID (該方法是線程安全的)
     * @return
     */
    public synchronized long nextId() {
        long timestamp = timeGen();

        // 如果當前時間小於上一次ID生成的時間戳，說明系統時鍾回退過這個時候應當拋出異常
        if (timestamp < lastTimestamp) {// 閏秒
            long offset = lastTimestamp - timestamp;
            if (offset <= 5) {
                try {
                    wait(offset << 1);
                    timestamp = timeGen();
                    if (timestamp < lastTimestamp) {
                        throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
                    }
                } catch (Exception e) {
                    throw new RuntimeException(e);
                }
            } else {
                throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", offset));
            }
        }

        // $NON-NLS-解決跨毫秒生成ID序列號始終為偶數的缺陷$
        // 如果是同一時間生成的，則進行毫秒內序列
        if (lastTimestamp == timestamp) {
            sequence = (sequence + 1) & sequenceMask;
            // 毫秒內序列溢出
            if (sequence == 0) {
                // 阻塞到下一個毫秒,獲得新的時間戳
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {// 時間戳改變，毫秒內序列重置
            sequence = 0L;
        }

        // 上次生成ID的時間截
        lastTimestamp = timestamp;
        // System.out.println("sequence-workerId:" + workerId    + "     sequence-datacenterId:" + datacenterId);
        // 移位並通過或運算拼到一起組成64位的ID
        return ((timestamp - twepoch) << timestampLeftShift)
                | (datacenterId << datacenterIdShift) //
                | (workerId << workerIdShift) //
                | sequence;
    }

    /**
     * 阻塞到下一個毫秒，直到獲得新的時間戳
     * @param lastTimestamp 上次生成ID的時間截
     * @return 當前時間戳
     */
    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }

        return timestamp;
    }

    /**
     * 返回以毫秒為單位的當前時間
     * @return 當前時間(毫秒)
     */
    protected long timeGen() {
        return System.currentTimeMillis();
    }

}

 

package com.test.domi.aspect;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.ResourceBundle;

public class SequenceWrapper {

    private static ResourceBundle resb = ResourceBundle.getBundle("serverInfo");

    private static String workerId = null;
    private static String datacenterId = null;
    private static Sequence sequence = null;


    public static String getNextId() {
        if (null == sequence) {
            workerId = getWorkerId();
            //workerId = "21";
            System.out.println("workerId: " + workerId);
            datacenterId = getDatacenterId();
            //datacenterId = "10";
            System.out.println("datacenterId: " + datacenterId);
            sequence = new Sequence(Long.valueOf(workerId), Long.valueOf(datacenterId));
        }
        return String.valueOf(sequence.nextId());
    }



    private static String getWorkerId() {
        FileReader fileReader;
        StringBuffer sb = new StringBuffer();

        try {
            String myidPath = resb.getString("api.path.myid");
            System.out.println("讀取myidPath為:" + myidPath);
            if ( null == myidPath || "".equals(myidPath) ) {
                sb.append("0");
            } else {
                System.out.println(myidPath);
                fileReader = new FileReader(myidPath);
                int ch = 0;
                while ((ch = fileReader.read()) != -1) {
                    sb.append((char) ch);
                }
            }
        } catch (FileNotFoundException e) {
            System.out.println("api.path.myid文件沒有找到!");
            //e.printStackTrace();
            sb.append("0");
        } catch (IOException e) {
            System.out.println("讀取api.path.myid文件出錯!");
            //e.printStackTrace();
            sb.append("0");
        } catch (Exception e) {
            System.out.println("其它異常,如resb讀取api.path.myid異常");
            //e.printStackTrace();
            sb.append("0");
        }
        String result;
        result = sb.toString();
        System.out.println("result:" + result);
        return result;
    }


    private static String getDatacenterId() {
        FileReader fileReader;
        StringBuffer sb = new StringBuffer();

        try {
            String myidPath = resb.getString("api.path.myid");
            System.out.println("讀取myidPath為:" + myidPath);
            if ( null == myidPath || "".equals(myidPath) ) {
                sb.append("0");
            } else {
                fileReader = new FileReader(myidPath);
                int ch = 0;
                while ((ch = fileReader.read()) != -1) {
                    sb.append((char) ch);
                }
            }
        } catch (FileNotFoundException e) {
            System.out.println("api.path.myid文件沒有找到!");
            //e.printStackTrace();
            sb.append("0");
        } catch (IOException e) {
            System.out.println("讀取api.path.myid文件出錯!");
            //e.printStackTrace();
            sb.append("0");
        } catch (Exception e) {
            System.out.println("其它異常,如resb讀取api.path.myid異常");
            //e.printStackTrace();
            sb.append("0");
        }
        String result;
        result = sb.toString();
        System.out.println("result:" + result);
        return result;
    }

}