永不重复的id生成器
![](https://img2018.cnblogs.com/blog/1502888/201904/1502888-20190426173517907-411442276.jpg)
(1)需要导入的包
主要用在格式化日FastDateFormat.getInstance("yyyyMMddHHmmssSSS");
<dependency>
<groupId>commons-lang</groupId>
<artifactId>commons-lang</artifactId>
<version>2.6</version>
</dependency>
(2)IdGenerator类
import org.apache.commons.lang3.time.FastDateFormat;
import java.net.InetAddress;
import java.net.UnknownHostException;
/**
* 与snowflake算法区别,返回字符串id,占用更多字节,但直观从id中看出生成时间
* 改写了生成时间的format方法
* @Project concurrency
*/
public enum IdGenerator {
INSTANCE;
private long workerId; //用ip地址最后几个字节标示
private long datacenterId = 0L; //可配置在properties中,启动时加载,此处默认先写成0
private long sequence = 0L;
private long workerIdBits = 8L; //节点ID长度
private long datacenterIdBits = 2L; //数据中心ID长度,可根据时间情况设定位数
private long sequenceBits = 12L; //序列号12位
private long workerIdShift = sequenceBits; //机器节点左移12位
private long datacenterIdShift = sequenceBits + workerIdBits; //数据中心节点左移14位
private long sequenceMask = -1L ^ (-1L << sequenceBits); //4095
private long lastTimestamp = -1L;
private static final FastDateFormat FAST_DATE_FORMAT = FastDateFormat.getInstance("yyyyMMddHHmmssSSS");
IdGenerator(){
workerId = 0x000000FF & getLastIP();
}
public synchronized String nextId() {
long timestamp = timeGen(); //获取当前毫秒数
//如果服务器时间有问题(时钟后退) 报错。
if (timestamp < lastTimestamp) {
throw new RuntimeException(String.format(
"Clock moved backwards. Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
}
//如果上次生成时间和当前时间相同,在同一毫秒内
if (lastTimestamp == timestamp) {
//sequence自增,因为sequence只有12bit,所以和sequenceMask相与一下,去掉高位
sequence = (sequence + 1) & sequenceMask;
//判断是否溢出,也就是每毫秒内超过4095,当为4096时,与sequenceMask相与,sequence就等于0
if (sequence == 0) {
timestamp = tilNextMillis(lastTimestamp); //自旋等待到下一毫秒
}
} else {
sequence = 0L; //如果和上次生成时间不同,重置sequence,就是下一毫秒开始,sequence计数重新从0开始累加
}
lastTimestamp = timestamp;
long suffix = (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;
//String datePrefix = DateFormatUtils.format(timestamp, "yyyyMMddHHmmssSSS");
String datePrefix = FAST_DATE_FORMAT.format(timestamp);
return datePrefix + suffix;
}
protected long tilNextMillis(long lastTimestamp) {
long timestamp = timeGen();
while (timestamp <= lastTimestamp) {
timestamp = timeGen();
}
return timestamp;
}
protected long timeGen() {
return System.currentTimeMillis();
}
private byte getLastIP(){
byte lastip = 0;
try{
InetAddress ip = InetAddress.getLocalHost();
byte[] ipByte = ip.getAddress();
lastip = ipByte[ipByte.length - 1];
} catch (UnknownHostException e) {
e.printStackTrace();
}
return lastip;
}
}
(3)使用举例
String id = IdGenerator.INSTANCE.nextId()