Java 雪花算法工具类
SnowFlake(Twitter_Snowflake)的结构如下(每部分用-分开):
0 - 0000000000 0000000000 0000000000 0000000000 0 - 00000 - 00000 - 000000000000
1位标识,由于long基本类型在Java中是带符号的,最高位是符号位,正数是0,负数是1,所以id一般是正数,最高位是0。
41位时间戳(毫秒级),不是存储当前时间的时间戳,而是存储时间戳的差值(当前时间戳 - 开始时间戳);
可以使用69年,年T = (1L << 41) / (1000L * 60 * 60 * 24 * 365) = 69。
10位的数据机器位,可以部署在1024个节点,包括5位datacenterId和5位workerId。
12位毫秒内的计数序列,计数顺序号支持每个节点每毫秒(同一机器,同一时间戳)产生4096个ID。
加起来64位刚好是一个long,整体上按照时间自增排序,且分布式系统内不会产生ID碰撞(由数据中心ID和机器ID作区分),效率较高。
import lombok.extern.slf4j.Slf4j;
import java.text.MessageFormat;
@Slf4j
public class Snowflake {
private static final long TWEPOCH = 946656000000L;
private static final long WORKER_ID_BITS = 5L;
private static final long DATA_CENTER_ID_BITS = 5L;
private static final long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
private static final long MAX_DATA_CENTER_ID = ~(-1L << DATA_CENTER_ID_BITS);
private static final long SEQUENCE_BITS = 12L;
private static final long WORKER_ID_SHIFT = SEQUENCE_BITS;
private static final long DATA_CENTER_ID_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS;
private static final long TIMESTAMP_LEFT_SHIFT = SEQUENCE_BITS + WORKER_ID_BITS + DATA_CENTER_ID_BITS;
private static final long SEQUENCE_MASK = ~(-1L << SEQUENCE_BITS);
private static final long STEP_SIZE = 1024;
private static final long UINT_MAX_VALUE = 0xffffffffL;
private long workerId;
private long workerIdFlags = 0L;
private long dataCenterId;
private long dataCenterIdFlags = 0L;
private long sequence = 0L;
private long basicSequence = 0L;
private long lastTimestamp = -1L;
private final WorkMode workMode;
public enum WorkMode {
NON_SHARED, RATE_1024, RATE_4096; }
public Snowflake() {
this(0, 0, WorkMode.RATE_4096);
}
public Snowflake(long workerId, long dataCenterId) {
this(workerId, dataCenterId, WorkMode.RATE_4096);
}
public Snowflake(long workerId, long dataCenterId, WorkMode workMode) {
this.workMode = workMode;
if (workerId > MAX_WORKER_ID || workerId < 0) {
throw new IllegalArgumentException(MessageFormat.format("worker Id can't be greater than {0} or less than 0", MAX_WORKER_ID));
}
if (dataCenterId > MAX_DATA_CENTER_ID || dataCenterId < 0) {
throw new IllegalArgumentException(MessageFormat.format("datacenter Id can't be greater than {0} or less than 0", MAX_DATA_CENTER_ID));
}
this.workerId = workerId;
this.workerIdFlags = setSpecifiedBitTo1(this.workerIdFlags, this.workerId);
this.dataCenterId = dataCenterId;
this.dataCenterIdFlags = setSpecifiedBitTo1(this.dataCenterIdFlags, this.dataCenterId);
}
public long getWorkerId() {
return workerId;
}
public long getDataCenterId() {
return dataCenterId;
}
public synchronized long nextId() {
long timestamp = timeGen();
if (timestamp < this.lastTimestamp) {
if (timestamp > TWEPOCH) {
if (WorkMode.NON_SHARED == this.workMode) {
nonSharedClockBackwards(timestamp);
} else if (WorkMode.RATE_1024 == this.workMode) {
rate1024ClockBackwards(timestamp);
} else {
throw new RuntimeException(MessageFormat.format("Clock moved backwards. Refusing to generate id for {0} milliseconds", lastTimestamp - timestamp));
}
} else {
throw new RuntimeException(MessageFormat.format("Clock moved backwards. Refusing to generate id for {0} milliseconds", lastTimestamp - timestamp));
}
}
if (this.lastTimestamp == timestamp) {
this.sequence = (this.sequence + 1) & SEQUENCE_MASK;
if (this.sequence == 0) {
timestamp = tilNextMillis(this.lastTimestamp);
}
}
else {
this.sequence = this.basicSequence;
}
this.lastTimestamp = timestamp;
return ((timestamp - TWEPOCH) << TIMESTAMP_LEFT_SHIFT)
| (this.dataCenterId << DATA_CENTER_ID_SHIFT)
| (this.workerId << WORKER_ID_SHIFT)
| this.sequence;
}
protected long tilNextMillis(long lastTimestamp) {
long timestamp0;
do {
timestamp0 = timeGen();
} while (timestamp0 <= lastTimestamp);
return timestamp0;
}
protected long timeGen() {
return System.currentTimeMillis();
}
private void nonSharedClockBackwards(long timestamp) {
if (this.dataCenterIdFlags >= UINT_MAX_VALUE && this.workerIdFlags >= UINT_MAX_VALUE) {
throw new RuntimeException(MessageFormat.format("Clock moved backwards. Refusing to generate id for {0} milliseconds", lastTimestamp - timestamp));
} else {
log.warn("Clock moved backwards. Refusing to generate id for {} milliseconds", lastTimestamp - timestamp);
if (this.dataCenterIdFlags >= UINT_MAX_VALUE) {
if (++this.workerId > MAX_WORKER_ID) {
this.workerId = 0L; }
this.workerIdFlags = setSpecifiedBitTo1(this.workerIdFlags, this.workerId);
this.dataCenterIdFlags = this.dataCenterId = 0L;
} else {
if (++this.dataCenterId > MAX_DATA_CENTER_ID) {
this.dataCenterId = 0L; }
}
this.dataCenterIdFlags = setSpecifiedBitTo1(this.dataCenterIdFlags, this.dataCenterId);
this.lastTimestamp = -1L;
log.warn("Try to fix the clock moved backwards. timestamp : {}, worker Id : {}, datacenter Id : {}", timestamp, workerId, dataCenterId);
}
}
private void rate1024ClockBackwards(long timestamp) {
if (this.basicSequence > (SEQUENCE_MASK - STEP_SIZE)) {
throw new RuntimeException(MessageFormat.format("Clock moved backwards. Refusing to generate id for {0} milliseconds", lastTimestamp - timestamp));
} else {
log.warn("Clock moved backwards. Refusing to generate id for {} milliseconds", lastTimestamp - timestamp);
this.basicSequence += STEP_SIZE;
this.lastTimestamp = -1L;
log.warn("Try to fix the clock moved backwards. timestamp : {}, basicSequence : {}", timestamp, basicSequence);
}
}
private long setSpecifiedBitTo1(long value, long index) {
return value |= (1L << index);
}
private long setSpecifiedBitTo0(long value, long index) {
return value &= ~(1L << index);
}
private int getSpecifiedBit(long value, long index) {
return (value & (1L << index)) == 0 ? 0 : 1;
}
}