com.jchanghong.core.lang.Snowflake Maven / Gradle / Ivy
package com.jchanghong.core.lang;
import com.jchanghong.core.date.SystemClock;
import com.jchanghong.core.util.StrUtil;
import java.io.Serializable;
import java.util.Date;
/**
* Twitter的Snowflake 算法
* 分布式系统中，有一些需要使用全局唯一ID的场景，有些时候我们希望能使用一种简单一些的ID，并且希望ID能够按照时间有序生成。
*
*
* snowflake的结构如下(每部分用-分开):
*
*
* 0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000
*
*
* 第一位为未使用(符号位表示正数)，接下来的41位为毫秒级时间(41位的长度可以使用69年)
* 然后是5位datacenterId和5位workerId(10位的长度最多支持部署1024个节点）
* 最后12位是毫秒内的计数（12位的计数顺序号支持每个节点每毫秒产生4096个ID序号）
*
* 并且可以通过生成的id反推出生成时间,datacenterId和workerId
*
* 参考：http://www.cnblogs.com/relucent/p/4955340.html
*
* @author Looly
* @since 3.0.1
*/
public class Snowflake implements Serializable {
private static final long serialVersionUID = 1L;
private final long twepoch;
private final long workerIdBits = 5L;
private final long dataCenterIdBits = 5L;
//// 最大支持机器节点数0~31，一共32个
// 最大支持数据中心节点数0~31，一共32个
@SuppressWarnings({"PointlessBitwiseExpression", "FieldCanBeLocal"})
private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
@SuppressWarnings({"PointlessBitwiseExpression", "FieldCanBeLocal"})
private final long maxDataCenterId = -1L ^ (-1L << dataCenterIdBits);
// 序列号12位
private final long sequenceBits = 12L;
// 机器节点左移12位
private final long workerIdShift = sequenceBits;
// 数据中心节点左移17位
private final long dataCenterIdShift = sequenceBits + workerIdBits;
// 时间毫秒数左移22位
private final long timestampLeftShift = sequenceBits + workerIdBits + dataCenterIdBits;
@SuppressWarnings({"PointlessBitwiseExpression", "FieldCanBeLocal"})
private final long sequenceMask = -1L ^ (-1L << sequenceBits);// 4095
private final long workerId;
private final long dataCenterId;
private final boolean useSystemClock;
private long sequence = 0L;
private long lastTimestamp = -1L;
/**
* 构造
*
* @param workerId 终端ID
* @param dataCenterId 数据中心ID
*/
public Snowflake(long workerId, long dataCenterId) {
this(workerId, dataCenterId, false);
}
/**
* 构造
*
* @param workerId 终端ID
* @param dataCenterId 数据中心ID
* @param isUseSystemClock 是否使用{@link SystemClock} 获取当前时间戳
*/
public Snowflake(long workerId, long dataCenterId, boolean isUseSystemClock) {
this(null, workerId, dataCenterId, isUseSystemClock);
}
/**
* @param epochDate 初始化时间起点（null表示默认起始日期）,后期修改会导致id重复,如果要修改连workerId dataCenterId，慎用
* @param workerId 工作机器节点id
* @param dataCenterId 数据中心id
* @param isUseSystemClock 是否使用{@link SystemClock} 获取当前时间戳
* @since 5.1.3
*/
public Snowflake(Date epochDate, long workerId, long dataCenterId, boolean isUseSystemClock) {
if (null != epochDate) {
this.twepoch = epochDate.getTime();
} else{
// Thu, 04 Nov 2010 01:42:54 GMT
this.twepoch = 1288834974657L;
}
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(StrUtil.format("worker Id can't be greater than {} or less than 0", maxWorkerId));
}
if (dataCenterId > maxDataCenterId || dataCenterId < 0) {
throw new IllegalArgumentException(StrUtil.format("datacenter Id can't be greater than {} or less than 0", maxDataCenterId));
}
this.workerId = workerId;
this.dataCenterId = dataCenterId;
this.useSystemClock = isUseSystemClock;
}
/**
* 根据Snowflake的ID，获取机器id
*
* @param id snowflake算法生成的id
* @return 所属机器的id
*/
public long getWorkerId(long id) {
return id >> workerIdShift & ~(-1L << workerIdBits);
}
/**
* 根据Snowflake的ID，获取数据中心id
*
* @param id snowflake算法生成的id
* @return 所属数据中心
*/
public long getDataCenterId(long id) {
return id >> dataCenterIdShift & ~(-1L << dataCenterIdBits);
}
/**
* 根据Snowflake的ID，获取生成时间
*
* @param id snowflake算法生成的id
* @return 生成的时间
*/
public long getGenerateDateTime(long id) {
return (id >> timestampLeftShift & ~(-1L << 41L)) + twepoch;
}
/**
* 下一个ID
*
* @return ID
*/
public synchronized long nextId() {
long timestamp = genTime();
if (timestamp < lastTimestamp) {
if(lastTimestamp - timestamp < 2000){
// 容忍2秒内的回拨，避免NTP校时造成的异常
timestamp = lastTimestamp;
} else{
// 如果服务器时间有问题(时钟后退) 报错。
throw new IllegalStateException(StrUtil.format("Clock moved backwards. Refusing to generate id for {}ms", lastTimestamp - timestamp));
}
}
if (timestamp == lastTimestamp) {
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}
lastTimestamp = timestamp;
return ((timestamp - twepoch) << timestampLeftShift) | (dataCenterId << dataCenterIdShift) | (workerId << workerIdShift) | sequence;
}
/**
* 下一个ID（字符串形式）
*
* @return ID 字符串形式
*/
public String nextIdStr() {
return Long.toString(nextId());
}
// ------------------------------------------------------------------------------------------------------------------------------------ Private method start
/**
* 循环等待下一个时间
*
* @param lastTimestamp 上次记录的时间
* @return 下一个时间
*/
private long tilNextMillis(long lastTimestamp) {
long timestamp = genTime();
// 循环直到操作系统时间戳变化
while (timestamp == lastTimestamp) {
timestamp = genTime();
}
if (timestamp < lastTimestamp) {
// 如果发现新的时间戳比上次记录的时间戳数值小，说明操作系统时间发生了倒退，报错
throw new IllegalStateException(
StrUtil.format("Clock moved backwards. Refusing to generate id for {}ms", lastTimestamp - timestamp));
}
return timestamp;
}
/**
* 生成时间戳
*
* @return 时间戳
*/
private long genTime() {
return this.useSystemClock ? SystemClock.now() : System.currentTimeMillis();
}
// ------------------------------------------------------------------------------------------------------------------------------------ Private method end
}