private static AtomicInteger uniqueId = new AtomicInteger(0);

public static String nextId() {
return Integer.toString(uniqueId.incrementAndGet());
}

private static final long ONE_STEP = 10;
private static final long BASE = 1129703383453l;

private static final Lock LOCK = new ReentrantLock();

private static long lastTime = System.currentTimeMillis();
private static short lastCount = 0;

/**
* a time (as returned by {@link System#currentTimeMillis()}) at which
* the VM that this UID was generated in was alive
* @serial
*/
private final long time;

/**
* 16-bit number to distinguish UID instances created
* in the same VM with the same time value
* @serial
*/
private final short count;

/**
* Generates a UID that is unique over time with
* respect to the host that it was generated on.
*/
public UID() {
LOCK.lock();
try {
if (lastCount == ONE_STEP) {
boolean done = false;
while (!done) {
long now = System.currentTimeMillis();
if (now == lastTime) {
// pause for a second to wait for time to change
try {
Thread.currentThread().sleep(1);
}
catch (java.lang.InterruptedException e) {
} // ignore exception
continue;
}
else {
lastTime = now;
lastCount = 0;
done = true;
}
}
}
time = lastTime;
count = lastCount++;
}
finally {
LOCK.unlock();
}
}