public static void setBlacklistedIPs(Set<String> blocked) {
        if (blocked == null) {
            throw new NullPointerException();
        }
        blockedIPs = blocked;
        if (blockedIPs.isEmpty()) {
            JiveGlobals.deleteProperty(ConnectionSettings.Client.LOGIN_BLOCKED);
        }
        else {
            // Iterate through the elements in the map.
            StringBuilder buf = new StringBuilder();
            Iterator<String> iter = blocked.iterator();
            if (iter.hasNext()) {
                buf.append(iter.next());
            }
            while (iter.hasNext()) {
                buf.append(", ").append(iter.next());
            }
            JiveGlobals.setProperty(ConnectionSettings.Client.LOGIN_BLOCKED, buf.toString());
        }
    }
Sets the list of IP address that are not allowed to connect to the server. This list is used for both anonymous
and non-anonymous users, and always takes precedence over a whitelist.

@param blocked the list of IP address that are not allowed to connect to the server. Can be empty, but not null.
xmppserver/src/main/java/org/jivesoftware/openfire/session/LocalClientSession.java