public void setAdminUsers(List<String> usernames) {
        if (adminList == null) {
            adminList = new ArrayList<>();
        }
        else {
            adminList.clear();
        }
        List<JID> admins = new ArrayList<>();
        for (String username : usernames) {
            admins.add(XMPPServer.getInstance().createJID(username, null));
        }
        adminList.addAll(admins);
        provider.setAdmins(admins);
    }
Sets the list of admin users based off of a list of usernames.  Clears list first.

@param usernames List of usernames to set as admins.
xmppserver/src/main/java/org/jivesoftware/openfire/admin/AdminManager.java