fxgl-multiplayer

name	fxgl-multiplayer
description	Add multiplayer and networking to an FXGL game — create TCP or WebSocket servers and clients via NetService, replicate entity spawns/positions/destruction across clients using MultiplayerService and NetworkComponent, synchronise player input, send and receive custom protocol messages, handle connect/disconnect events, and download files asynchronously. Use this skill when building a multiplayer game, a client-server architecture, a real-time entity sync system, or any network-connected feature in FXGL.
triggers	["multiplayer","network","NetService","MultiplayerService","NetworkComponent","TCP server","WebSocket","entity replication","server client","online game"]
compatibility	Java 17+, FXGL 21.x. Network requires open ports and matching client/server FXGL versions.
category	fxgl/multiplayer
tags	["fxgl","java","javafx","multiplayer"]
metadata	{"author":"fxgl-skills","version":"1.0","fxgl-version":"21.1"}
allowed-tools	["Read","Write","Edit","Bash"]

FXGL Multiplayer & Networking

Architecture

FXGL uses an authoritative server model:

• The server runs the game loop, processes input, and broadcasts world state.
• Clients send input events and render received state.
• MultiplayerService handles entity spawn/destroy/position replication.

Setup

// Both server and client need this in initSettings
settings.addEngineService(MultiplayerService.class);

Server Side

// Create TCP server
Server<Bundle> server = getNetService().newTCPServer(55555);

server.setOnConnected(conn -> {
    System.out.println("Client connected: " + conn.getConnectionNum());
    // Sync existing world state to the new client
    getService(MultiplayerService.class).addEntityReplicationSender(server, conn);
});

server.setOnDisconnected(conn -> {
    System.out.println("Client disconnected: " + conn.getConnectionNum());
    // Remove their player entity
});

// Listen for input from clients
server.setOnMessage((conn, bundle) -> {
    String type = bundle.getString("type");
    if ("input".equals(type)) {
        String action = bundle.getString("action");
        boolean active = bundle.getBoolean("active");
        handleClientInput(conn.getConnectionNum(), action, active);
    }
});

// Start listening
server.startAsync();

Client Side

// Connect to server
Client<Bundle> client = getNetService().newTCPClient("localhost", 55555);

client.setOnConnected(conn -> {
    System.out.println("Connected to server");
    getService(MultiplayerService.class).addEntityReplicationReceiver(conn, getGameWorld());
});

client.setOnMessage((conn, bundle) -> {
    
});


   {
        ();
    bundle.put(,   );
    bundle.put(, actionName);
    bundle.put(, isActive);
    client.getConnection().send(bundle);
}

client.connectAsync();