Source:Capturing browser logs with Selenium WebDriver using Java
int[] vals = new int[n];
for(int i = 0; i < n; i++) {
vals[i] = i;
}
// fischer yates shuffle
for(int i = n-1; i > 0; i--) {
int idx = rand.nextInt(i + 1);
int t = vals[idx];
vals[idx] = vals[i];
vals[i] = t;
}