PacketHandler

public class PacketHandler {

    public static int networkId = 0;

    private static final String NETWORK_PROTOCOL_VERSION = "1";
    public static final SimpleChannel CHANNEL = NetworkRegistry.newSimpleChannel(
            new ResourceLocation(Main.MOD_ID, "main"),
            () -> NETWORK_PROTOCOL_VERSION,
            NETWORK_PROTOCOL_VERSION::equals,
            NETWORK_PROTOCOL_VERSION::equals
    );

    public static void register() {
        CHANNEL.registerMessage(networkId++,
                PacketUpdateContainer.class,
                PacketUpdateContainer::encode,
                PacketUpdateContainer::decode,
                PacketUpdateContainer::handle,
                Optional.of(NetworkDirection.PLAY_TO_SERVER)
        );
    }

    public static void sendToServer(Object message) {
        CHANNEL.sendToServer(message);
    }
}