com.yuweix.kuafu.core.Snowflake Maven / Gradle / Ivy
package com.yuweix.kuafu.core;
import java.net.InetAddress;
import java.net.NetworkInterface;
import java.util.Enumeration;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @author yuwei
*/
public class Snowflake {
private static final long twepoch = 1288834974657L;
/**
* 机器标识位数
*/
private static final long workerIdBits = 5L;
/**
* 数据中心标识位数
*/
private static final long dataCenterIdBits = 5L;
/**
* 机器ID最大值
*/
// private static final long maxWorkerId = -1L ^ (-1L << workerIdBits);
/**
* 数据中心ID最大值
*/
// private static final long maxDataCenterId = -1L ^ (-1L << dataCenterIdBits);
/**
* 毫秒内自增位
*/
private static final long sequenceBits = 12L;
/**
* 机器ID左移位数
*/
private static final long workerIdShift = sequenceBits;
/**
* 数据中心ID左移位数
*/
private static final long dataCenterIdShift = sequenceBits + workerIdBits;
/**
* 时间毫秒左移位数
*/
private static final long timestampLeftShift = sequenceBits + workerIdBits + dataCenterIdBits;
private static final long sequenceMask = -1L ^ (-1L << sequenceBits);
private long workerId;
private long dataCenterId;
private long sequence = 0L;
private long lastTimestamp = -1L;
private Snowflake() {
this(getMachineId(), getMachineId());
}
private Snowflake(long workerId, long dataCenterId) {
this.workerId = workerId;
this.dataCenterId = dataCenterId;
}
public static Snowflake create() {
return new Snowflake();
}
public static Snowflake create(long workerId, long dataCenterId) {
return new Snowflake(workerId, dataCenterId);
}
private static volatile Snowflake DEFAULT_INSTANCE = null;
private static final Lock LOCK = new ReentrantLock();
private static Snowflake get() {
if (DEFAULT_INSTANCE == null) {
try {
LOCK.lock();
if (DEFAULT_INSTANCE == null) {
DEFAULT_INSTANCE = new Snowflake();
}
} finally {
LOCK.unlock();
}
}
return DEFAULT_INSTANCE;
}
public static long getId() {
return get().nextId();
}
/**
* 18位
*/
public synchronized long nextId() {
//时间戳
long timestamp = System.currentTimeMillis();
if (timestamp < lastTimestamp) {
throw new RuntimeException(String.format("Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
}
if (timestamp == lastTimestamp) {
//当前毫秒内，则+1
sequence = (sequence + 1) & sequenceMask;
if (sequence == 0) {
//当前毫秒内计数满了，则等待下一秒
timestamp = tillNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}
lastTimestamp = timestamp;
//ID偏移组合生成最终的ID，并返回ID
return ((timestamp - twepoch) << timestampLeftShift) | (dataCenterId << dataCenterIdShift) | (workerId << workerIdShift) | sequence;
}
private long tillNextMillis(long lastTimestamp) {
long timestamp = System.currentTimeMillis();
while (timestamp <= lastTimestamp) {
timestamp = System.currentTimeMillis();
}
return timestamp;
}
/**
* 获取机器id
*/
private static long getMachineId() {
long machineId = 0;
try {
for (Enumeration interfaces = NetworkInterface.getNetworkInterfaces(); interfaces.hasMoreElements();) {
NetworkInterface networkInterface = interfaces.nextElement();
if (networkInterface.isLoopback() || networkInterface.isVirtual() || !networkInterface.isUp()) {
continue;
}
Enumeration addresses = networkInterface.getInetAddresses();
if (addresses.hasMoreElements()) {
String ipAddress = addresses.nextElement().getHostAddress();
machineId = Math.abs(ipAddress.hashCode() % 32);
}
}
} catch (Exception e) {
e.printStackTrace();
}
return machineId;
}
}