分布式唯一ID生成器

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * 53 bits unique id:
 *
 * |--------|--------|--------|--------|--------|--------|--------|--------|
 * |00000000|00011111|11111111|11111111|11111111|11111111|11111111|11111111|
 * |--------|---xxxxx|xxxxxxxx|xxxxxxxx|xxxxxxxx|xxx-----|--------|--------|
 * |--------|--------|--------|--------|--------|---xxxxx|xxxxxxxx|xxx-----|
 * |--------|--------|--------|--------|--------|--------|--------|---xxxxx|
 *
 * Maximum ID = 11111_11111111_11111111_11111111_11111111_11111111_11111111
 *
 * Maximum TS(TimeStamp 时间戳  32位) = 11111_11111111_11111111_11111111_111
 *
 * Maximum NT(每秒生成最多生成的ID数  16位) = ----- -------- -------- -------- ---11111_11111111_111 = 65535
 *
 * Maximum SH(分片数-机器数  5位) = ----- -------- -------- -------- -------- -------- ---11111 = 31
 *
 * It can generate 64k unique id per IP and up to 2136-02-07T06:28:15Z.
 */
public final class IdUtils {

    private static final Logger logger = LoggerFactory.getLogger(IdUtils.class);

    private static final Pattern PATTERN_LONG_ID = Pattern.compile("^([0-9]{15})([0-9a-f]{32})([0-9a-f]{3})$");

    private static final Pattern PATTERN_HOSTNAME = Pattern.compile("^.*\\D+([0-9]+)$");

    private static final long OFFSET = LocalDate.of(2000, 1, 1).atStartOfDay(ZoneId.of("Z")).toEpochSecond();

    private static final long MAX_NEXT = 0b11111_11111111_111L;

    private static final long SHARD_ID = getServerIdAsLong();

    private static long offset = 0;

    private static long lastEpoch = 0;

    public static long nextId() {
        return nextId(System.currentTimeMillis() / 1000);
    }

    private static synchronized long nextId(long epochSecond) {
        if (epochSecond < lastEpoch) {
            // warning: clock is turn back:
            logger.warn("clock is back: " + epochSecond + " from previous:" + lastEpoch);
            epochSecond = lastEpoch;
        }
        if (lastEpoch != epochSecond) {
            lastEpoch = epochSecond;
            reset();
        }
        offset++;
        long next = offset & MAX_NEXT;
        if (next == 0) {
            logger.warn("maximum id reached in 1 second in epoch: " + epochSecond);
            return nextId(epochSecond + 1);
        }
        return generateId(epochSecond, next, SHARD_ID);
    }

    private static void reset() {
        offset = 0;
    }

    private static long generateId(long epochSecond, long next, long shardId) {
        return ((epochSecond - OFFSET) << 21) | (next << 5) | shardId;
    }

    private static long getServerIdAsLong() {
        try {
            String hostname = InetAddress.getLocalHost().getHostName();
            Matcher matcher = PATTERN_HOSTNAME.matcher(hostname);
            if (matcher.matches()) {
                long n = Long.parseLong(matcher.group(1));
                if (n >= 0 && n < 8) {
                    logger.info("detect server id from host name {}: {}.", hostname, n);
                    return n;
                }
            }
        } catch (UnknownHostException e) {
            logger.warn("unable to get host name. set server id = 0.");
        }
        return 0;
    }

    public static long stringIdToLongId(String stringId) {
        // a stringId id is composed as timestamp (15) + uuid (32) + serverId (000~fff).
        Matcher matcher = PATTERN_LONG_ID.matcher(stringId);
        if (matcher.matches()) {
            long epoch = Long.parseLong(matcher.group(1)) / 1000;
            String uuid = matcher.group(2);
            byte[] sha1 = HashUtil.sha1AsBytes(uuid);
            long next = ((sha1[0] << 24) | (sha1[1] << 16) | (sha1[2] << 8) | sha1[3]) & MAX_NEXT;
            long serverId = Long.parseLong(matcher.group(3), 16);
            return generateId(epoch, next, serverId);
        }
        throw new IllegalArgumentException("Invalid id: " + stringId);
    }
}

思考：如果只是要保证每个月内的不相同，则可以把时间戳位数进一步减少。 OFFSET的值就取每月开始的epochSecond

转自廖雪峰老师的分布式唯一ID生成器