* Saves the buffered groups to file
* @param filename - The groupdata file to write to
*/
public static void save(String filename) {
synchronized (managers) {
new DataWriter(filename) {
public void write(DataOutputStream stream) throws IOException {
//clear empty worlds
Iterator<OfflineGroupManager> iter = managers.values().iterator();
while (iter.hasNext()) {
if (iter.next().groupmap.isEmpty()) {