package com.doumee.core.utils;
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import org.apache.logging.log4j.util.Strings;
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import java.util.UUID;
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/**
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* A utility to generate id using various strategies.
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*
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* @author Guang YANG
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* @version 1.0
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*/
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public class ID {
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private static final SnowflakeIdGenerator snowflake = new SnowflakeIdGenerator(0);
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/**
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* Generate a random guid string of 32 byte.
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*/
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public static String nextGUID() {
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return UUID.randomUUID().toString().replace("-", Strings.EMPTY).toUpperCase();
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}
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/**
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* Generate a random uuid string of 36 byte.
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*/
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public static String nextUUID() {
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return UUID.randomUUID().toString();
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}
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/**
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* Generate a long number of 20 bit which is monotonically increasing by each call.
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*/
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public static long nextSnowflakeId() {
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return snowflake.nextId();
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}
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public static class SnowflakeIdGenerator {
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private final long workerIdBits = 10L;
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private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
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private final long sequenceBits = 12L;
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private final long workerIdShift = sequenceBits;
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private final long timestampLeftShift = sequenceBits + workerIdBits;
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private final long sequenceMask = -1L ^ (-1L << sequenceBits);
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private long workerId;
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private long sequence = 0L;
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private long lastTimestamp = -1L;
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public SnowflakeIdGenerator(long workerId) {
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if (workerId > maxWorkerId || workerId < 0) {
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throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
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}
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this.workerId = workerId;
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}
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public synchronized long nextId() {
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long timestamp = System.currentTimeMillis();
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if (timestamp < lastTimestamp) {
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throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
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}
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if (lastTimestamp == timestamp) {
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sequence = (sequence + 1) & sequenceMask;
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if (sequence == 0) {
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timestamp = tilNextMillis(lastTimestamp);
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}
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} else {
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sequence = 0L;
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}
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lastTimestamp = timestamp;
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return (timestamp << timestampLeftShift) | (workerId << workerIdShift) | sequence;
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}
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protected long tilNextMillis(long lastTimestamp) {
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long timestamp = System.currentTimeMillis();
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while (timestamp <= lastTimestamp) {
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timestamp = System.currentTimeMillis();
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}
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return timestamp;
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}
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}
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}
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