【02】ZooKeeper经典应用场景实战一
public class SnowflakeIdGenerator {
/**
* 单例
*/
public static SnowflakeIdGenerator instance =
new SnowflakeIdGenerator();
/**
* 初始化单例
*
* @param workerId 节点Id,最大8091
* @return the 单例
*/
public synchronized void init(long workerId) {
if (workerId > MAX_WORKER_ID) {
// zk分配的workerId过大
throw new IllegalArgumentException("woker Id wrong: " + workerId);
}
instance.workerId = workerId;
}
private SnowflakeIdGenerator() {
}
/**
* 开始使用该算法的时间为: 2017-01-01 00:00:00
*/
private static final long START_TIME = 1483200000000L;
/**
* worker id 的bit数，最多支持8192个节点
*/
private static final int WORKER_ID_BITS = 13;
/**
* 序列号，支持单节点最高每毫秒的最大ID数1024
*/
private final static int SEQUENCE_BITS = 10;
/**
* 最大的 worker id ，8091
* -1 的补码（二进制全1）右移13位, 然后取反
*/
private final static long MAX_WORKER_ID = ~(-1L << WORKER_ID_BITS);
/**
* 最大的序列号，1023
* -1 的补码（二进制全1）右移10位, 然后取反
*/
private final static long MAX_SEQUENCE = ~(-1L << SEQUENCE_BITS);
/**
* worker 节点编号的移位
*/
private final static long WORKER_ID_SHIFT = SEQUENCE_BITS;
/**
* 时间戳的移位
*/
private final static long TIMESTAMP_LEFT_SHIFT = WORKER_ID_BITS + SEQUENCE_BITS;
/**
* 该项目的worker 节点 id
*/
private long workerId;
/**
* 上次生成ID的时间戳
*/
private long lastTimestamp = -1L;
/**
* 当前毫秒生成的序列
*/
private long sequence = 0L;
/**
* Next id long.
*
* @return the nextId
*/
public Long nextId() {
return generateId();
}
/**
* 生成唯一id的具体实现
*/
private synchronized long generateId() {
long current = System.currentTimeMillis();
if (current < lastTimestamp) {
// 如果当前时间小于上一次ID生成的时间戳，说明系统时钟回退过，出现问题返回-1
return -1;
}
if (current == lastTimestamp) {
// 如果当前生成id的时间还是上次的时间，那么对sequence序列号进行+1
sequence = (sequence + 1) & MAX_SEQUENCE;
if (sequence == MAX_SEQUENCE) {
// 当前毫秒生成的序列数已经大于最大值，那么阻塞到下一个毫秒再获取新的时间戳
current = this.nextMs(lastTimestamp);
}
} else {
// 当前的时间戳已经是下一个毫秒
sequence = 0L;
}
// 更新上次生成id的时间戳
lastTimestamp = current;
// 进行移位操作生成int64的唯一ID
//时间戳右移动23位
long time = (current - START_TIME) << TIMESTAMP_LEFT_SHIFT;
//workerId 右移动10位
long workerId = this.workerId << WORKER_ID_SHIFT;
return time | workerId | sequence;
}
/**
* 阻塞到下一个毫秒
*/
private long nextMs(long timeStamp) {
long current = System.currentTimeMillis();
while (current <= timeStamp) {
current = System.currentTimeMillis();
}
return current;
}
}