A production-grade, real-time multi-client chat system built from scratch using raw Java Sockets — no frameworks, no shortcuts. Powered by Groq AI for toxicity detection and smart replies.

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👨‍💻 Authors

Devanshu Sharma

Sanmati Jain

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✨ Features

Feature	Description
🔌 Raw TCP Chat	Multi-client real-time chat using Java ServerSocket — zero frameworks
🧵 Thread per Client	Dedicated ClientHandler thread for each connected user
🏠 Multiple Rooms	Create, join, and leave chat rooms dynamically
🤖 AI Toxicity Detection	Groq AI (Llama 3.3 70B) scans every message before broadcast
💡 Smart Replies	/ai command generates 3 context-aware reply suggestions
🌐 Browser Support	WebSocket → TCP proxy bridges browser clients to Java server
📡 REST API	Full HTTP API for rooms, history, stats
💬 Private Messaging	Direct messages between users via /pm command

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🏗️ Architecture

Browser Clients
      │  WebSocket (ws://localhost:3001)
      ▼
 ┌─────────────┐
 │  proxy.js   │  Node.js WebSocket → TCP Bridge
 └──────┬──────┘
        │  TCP (port 9291)
        ▼
 ┌──────────────────────────────────────┐
 │         Java Chat Server             │
 │  ┌─────────────┐  ┌───────────────┐ │
 │  │ ChatServer  │  │  RestApiServer│ │
 │  │  port 9291  │  │   port 8281   │ │
 │  └──────┬──────┘  └───────────────┘ │
 │         │                           │
 │  ┌──────▼──────┐  ┌───────────────┐ │
 │  │ClientHandler│  │  AIService    │ │
 │  │(per thread) │  │  Groq API     │ │
 │  └─────────────┘  └───────────────┘ │
 └──────────────────────────────────────┘

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📁 Project Structure

chat-system/
├── 📄 pom.xml
├── 📄 README.md
├── 📂 frontend/
│   ├── 🌐 index.html          ← Single page UI
│   ├── ⚡ proxy.js             ← WebSocket → TCP bridge
│   └── 🔁 restart_servers.ps1
├── 📂 src/main/java/com/chat/
│   ├── 🚀 Main.java
│   ├── 📂 chat/
│   │   ├── ChatServer.java     ← ServerSocket server
│   │   ├── ClientHandler.java  ← Thread per client
│   │   └── CommandProcessor.java
│   ├── 📂 server/
│   │   └── RestApiServer.java  ← HTTP API (port 8281)
│   ├── 📂 services/
│   │   ├── MessageService.java
│   │   └── AIService.java      ← Groq AI integration
│   ├── 📂 models/
│   ├── 📂 exceptions/
│   └── 📂 utils/
│       └── ApiConfig.java
└── 🧪 tcp_test.js

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🚀 Quick Start

Prerequisites

• Java 17+
• Maven 3.8+
• Node.js 18+
• Free Groq API key → console.groq.com (no card needed)

1. Clone the repo

git clone https://github.com/Devanshu11976/Chat-System.git
cd Chat-System/chat-system

2. Set your Groq API key

# PowerShell
$env:GROQ_API_KEY="your_groq_key_here"

# Mac / Linux
export GROQ_API_KEY="your_groq_key_here"

3. Build & run the Java server

# Build
mvn package

# Run (PowerShell)
$env:CHAT_SOCKET_PORT='9291'
$env:CHAT_REST_PORT='8281'
java -cp "target\classes;lib\json-20231013.jar" com.chat.Main

4. Start the WebSocket proxy

# Open a new terminal
cd frontend
$env:WS_PORT='3001'
$env:CHAT_PORT='9291'
node proxy.js

5. Open the frontend

Open frontend/index.html in your browser

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🌐 REST API Endpoints

Method	Endpoint	Description
GET	/api/rooms	List all chat rooms
GET	/api/rooms/{roomId}	Room details + members
GET	/api/rooms/{roomId}/history	Message history
GET	/api/users	Online users
GET	/api/stats	Server statistics
GET	/api/moderation/log	AI toxicity log

Example

curl http://localhost:8281/api/rooms
curl http://localhost:8281/api/stats

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💬 Chat Commands

Command	Description
/join <room>	Join or create a room
/leave	Leave current room
/msg <text>	Send message to room
/pm <username> <text>	Private message
/ai <context>	Get 3 AI smart reply suggestions
/users	List users in current room
/rooms	List all active rooms
/quit	Disconnect

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🤖 AI Features

Toxicity Detection

Every message is analyzed by Groq AI (Llama 3.3 70B) before broadcast:

Score	Action	Display
0 – 30	✅ Allow	Normal message
31 – 60	⚠️ Warn	Flagged with warning tag
61 – 100	🚫 Block	Hidden + sender notified

3 blocked messages → automatic disconnect

Smart Replies (/ai)

Generates 3 context-aware reply suggestions with tone labels: friendly · professional · casual · funny

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🔌 Ports Reference

Service	Default Port	Env Variable
Java TCP Chat Server	9291	CHAT_SOCKET_PORT
Java REST API	8281	CHAT_REST_PORT
Node WebSocket Proxy	3001	WS_PORT

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🧪 Testing

# Run the automated TCP test
node tcp_test.js

This script connects via TCP, sets a username, creates the autotest room, sends a message, and verifies server responses automatically.

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🐛 Troubleshooting

Port already in use

# Find and kill the process
netstat -ano | findstr :9291
taskkill /PID <pid> /F

Frontend not connecting

• Make sure proxy.js is running on port 3001
• Check WS_URL constant in frontend/index.html matches proxy port
• Verify REST API is up: curl http://localhost:8281/api/rooms

"Unknown command" in chat

• Check proxy.log — proxy forwards raw text to TCP
• Ensure command format is exact, e.g. /join general not /join/general

AI not responding

• Verify GROQ_API_KEY env variable is set
• App has automatic fallback to keyword-based moderation if Groq is unavailable

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🛠️ Tech Stack

Layer	Technology
Chat Server	Java 17 · ServerSocket · ConcurrentHashMap
Threading	Thread per client · AtomicInteger · synchronized
REST API	com.sun.net.httpserver.HttpServer
JSON	org.json
WS Bridge	Node.js · ws library
AI	Groq API · Llama 3.3 70B
Build	Maven

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📜 License

MIT © 2026 Devanshu Sharma & Sanmati Jain

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Built with ❤️ using raw Core Java — no frameworks, no shortcuts.

"If you can't explain it without a framework, you don't understand it."

💜 Made with love by Dev & San