java 利用时间生成主键

import java.util.ArrayList;
import java.util.List;
import java.util.Random;


public final class GeneratedKeys {

    private static final Random     RANDOM                   = new Random();
    private static final int        MAX_SIZE                 = 1050;        //最多不超过1050条
    private static final List<Long> LOCAL_TIMESTAMP_KEY_POOL = new ArrayList<>(MAX_SIZE);


    /**
     * 利用本地生成时间戳，为主键
     *
     * @return
     */
    static synchronized public long localTimestampKey() {
        //若是本地主键池中大于MAX_SIZE个，那么就将其清除，防止内存溢出
        if (LOCAL_TIMESTAMP_KEY_POOL.size() > MAX_SIZE) {
            LOCAL_TIMESTAMP_KEY_POOL.subList(LOCAL_TIMESTAMP_KEY_POOL.size() - 120, LOCAL_TIMESTAMP_KEY_POOL.size()).clear();
        }

        long timeStamp = System.currentTimeMillis() * 1000 + getSlot();
        while (LOCAL_TIMESTAMP_KEY_POOL.contains(timeStamp)) {
            int i = 110000;    //在此等侍
            while (i > 0) {
                i--;
            }
            timeStamp = System.currentTimeMillis() * 1000 + getSlot();
        }
        LOCAL_TIMESTAMP_KEY_POOL.add(0, timeStamp);
        return timeStamp;
    }

    /**
     * 获取111-999 之间的数
     *
     * @author Canaan
     * @date 2019/6/9 18:33
     */
    private static int getSlot() {
        StringBuilder slot = new StringBuilder();
        for (int i = 0; i < 3; i++) {
            slot.append(RANDOM.nextInt(10));
        }
        return Integer.valueOf(slot.toString());
    }


}

 

这个不能集群使用