Java生成唯一的ID

public class UIDGenerator {
private static Date date = new Date();
private static StringBuilder buf = new StringBuilder();
private static int seq = 0;
private static final int ROTATION = 99999;
public static synchronized long next(){
if (seq > ROTATION) seq = 0;
buf.delete(0, buf.length());
date.setTime(System.currentTimeMillis());
String str = String.format("%1$tY%1$tm%1$td%1$tk%1$tM%1$tS%2$05d", date, seq++);
return Long.parseLong(str);
}
}