java单例模式生成数据库主键

/**
*
* 生成主键的工具类
* 主键的格式为：当前时间+0~9
*
*/
public class IdUtils {

private static IdUtils instance = null;
private static final long COUNT_SUM = 10;
private static long lastTime = System.currentTimeMillis();
private static short currentCount = 0;

private IdUtils() {
}

public static synchronized IdUtils getInstance() {
if (instance == null) {
instance = new IdUtils();
}
return instance;
}

/**
* 用来产生唯一id
*
* @return
*/
public synchronized String getUID() {
if (currentCount == COUNT_SUM) {
boolean done = false;
while (!done) {
long nowTime = System.currentTimeMillis();
if (nowTime == lastTime) {
try {
Thread.sleep(1);// 可以保证当前得到的时间和上一次的时间不一致
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
continue;
} else {
lastTime = nowTime;
currentCount = 0;
done = true;
}
}
}
return lastTime + "" + (currentCount++);
}

}

public class demo {

public static void main(String[]args){
for(int i=0;i<20;i++){
System.out.println(IdUtils.getInstance().getUID());
}
}
}