Multiplayer Platformer

A basic, but difficult, platformer game with levels stored in JSON for easy editing. The server uses sockets to communicate information between itself and all connected clients. First networking project!

Features

• Real-time multiplayer over TCP sockets — up to 10 players per server
• Levels defined entirely in JSON (levels.json), including walls, death boxes, checkpoints, trampolines, ice, and finish lines
• Players advance to the next level together once everyone reaches the finish line
• In-game chat between players
• Zoom and pan camera controls

Tech Stack

• Java 21
• Maven
• org.json for level parsing
• Java Swing for the client GUI
• Raw java.net.Socket / ServerSocket for client-server communication

Getting Started

Build

mvn package

This produces two runnable jars in target/:

• SimpleMultiplayerGameServer-server.jar — the game server
• SimpleMultiplayerGameServer-client.jar — the game client

Run the server

java -jar target/SimpleMultiplayerGameServer-server.jar

The server listens on port 8888.

Run a client

java -jar target/SimpleMultiplayerGameServer-client.jar

Enter the server's IP address and port (8888) in the client window to connect.

Controls

Action	Key(s)
Move	WASD / Arrow keys
Jump	W / Up / Space
Zoom	Mouse scroll
Pan camera	Mouse drag
Chat	Enter

Editing Levels

Levels live in src/main/resources/levels.json as an array of levels, each an array of objects. Every object has a type along with the fields it needs:

• Spawn — x, y starting position for the level
• Wall, Checkpoint, FinishLine, DeathBox, Trampoline, Ice — x, y, w, h, color, and an optional equation for moving platforms
• Tip — x, y, w, h, message shown when a player enters the area

Add a new level by appending another array to the top-level JSON array — no code changes required.

Project Structure

src/main/java/
├── client/
│   ├── game/       # Game loop, rendering, server connection handling
│   ├── objects/    # Player, Box, Level, and other game objects
│   └── utility/    # Shared helpers (messages, vectors, ping)
└── server/         # GameServer and per-client connection handling
src/main/resources/
└── levels.json     # Level definitions