基于Twitter 的分布式唯一ID生成工具类

import java.net.InetAddress;
import java.net.NetworkInterface;

/**
* @author zhang.xiaoming
*/
public class IDGenerater {

private static String hexStr =  "0123456789ABCDEF";

private final long twepoch = 1288834974657L;
// 机器标识位数
private final long workerIdBits = 28L;
// 数据中心标识位数
private final long datacenterIdBits = 24L;
// 机器ID最大值
private final long maxWorkerId = -1L ^ (-1L << workerIdBits);
// 数据中心ID最大值
private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
// 毫秒内自增位
private final long sequenceBits = 12L;
// 机器ID偏左移12位
private final long workerIdShift = sequenceBits;
// 数据中心ID左移40位
private final long datacenterIdShift = sequenceBits + workerIdBits;
// 时间毫秒左移26位
private final long timestampLeftShift = 26;
private final long sequenceMask = -1L ^ (-1L << sequenceBits);

private long workerId;
private long datacenterId;
private long sequence = 0L;
private long lastTimestamp = -1L;

public IDGenerater_B() {
// 用IP地址初始化 workerId datacenterId;
workerId = getMACAddress();
datacenterId = getThreadId();
if (workerId > maxWorkerId || workerId < 0) {
throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
}
if (datacenterId > maxDatacenterId || datacenterId < 0) {
throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
}
this.workerId = workerId;
this.datacenterId = datacenterId;
}

public synchronized String nextId() {
long timestamp = timeGen();
if (timestamp < lastTimestamp) {
throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
}
if (lastTimestamp == timestamp) {
//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 = tilNextMillis(lastTimestamp);
}
} else {
sequence = 0L;
}

lastTimestamp = timestamp;
// ID偏移组合生成最终的ID，并返回ID
return getResult(Long.toBinaryString(((timestamp - twepoch) << timestampLeftShift)) +Long.toBinaryString((datacenterId << datacenterIdShift+(datacenterIdBits-Long.toBinaryString(datacenterId).length())) | (workerId << workerIdShift) | sequence));
}

// 等待下一个毫秒的到来
protected long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}

protected long timeGen() {
return System.currentTimeMillis();
}

// 获取MAC地址
private  long getMACAddress(){
// 获得网络接口对象（即网卡），并得到mac地址，mac地址存在于一个byte数组中。
try {
InetAddress localhost= InetAddress.getLocalHost();
byte[] mac = NetworkInterface.getByInetAddress(localhost).getHardwareAddress();
long macSum=0l;
for(int i=0;i<mac.length;i++){
//mac[i] & 0xFF 是为了把byte转化为正整数
macSum += (mac[i] & 0xFF);
}
return macSum;
} catch (Exception e) {
e.printStackTrace();
}
return 0;
}

// 获取当前线程ID
private  long getThreadId() {
return Thread.currentThread().getId();
}

private String getResult(String ResultBinary){
String str1="";
char arr[]=new char[ResultBinary.length()/4];
for(int i=0;i<ResultBinary.length();i++){
str1+=ResultBinary.charAt(i);
if((i+1)%4==0){
arr[i/4]=bin2HexStr(str1);
str1="";
}
}
return String.valueOf(arr);
}

private char bin2HexStr(String str){
int sum = Integer.parseInt(str.charAt(0)+"")*8+Integer.parseInt(str.charAt(1)+"")*4+Integer.parseInt(str.charAt(2)+"")*2+Integer.parseInt(str.charAt(3)+"")*1;
return hexStr.charAt(sum);
}

public static void main(String[] args) {
IDGenerater IDGenerater = new IDGenerater();
for (int i = 0; i < 10; i++) {
String id = IDGenerater.nextId();
System.out.println(id);
}
}
}