🚀 Multi-Threaded File Server

A Java implementation of a multi-threaded TCP file server that allows multiple clients to connect simultaneously and download files using a simple set of commands presented in a terminal interface.

Overview

This project implements a multi-threaded TCP file server in Java that allows multiple clients to connect simultaneously and request files from a shared directory. The server handles each client connection in a dedicated thread, ensuring efficient and parallel file serving.

Synchronization is achieved using the synchronized keyword on all shared data structures, preventing race conditions and ensuring data consistency across concurrent threads.

This project was developed as part of the Concurrent and Network Programming module (IRISI 2 — University Cadi Ayyad, 2025–2026). The goal was to apply fundamental concepts of concurrent programming such as threads, synchronization, and TCP socket communication to build a real distributed file-sharing application.

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Features

• Multiple simultaneous client connections
• Dedicated thread per client (ClientHandler)
• LIST command — list all available files on the server
• GET <filename> command — download any file (text or binary)
• QUIT command — cleanly disconnect from the server
• Synchronized shared state (connected clients, operation log, download counter)
• Automatic server statistics printed every 20 seconds
• Graceful handling of abrupt client disconnections
• Multi-client test class to simulate a concurrent load

Project Structure

MultiThreaded-File-Server/
├── src/
│   ├── FileServer.java        # Main server — listens on port 12346
│   ├── ClientHandler.java     # Handles one client per thread
│   ├── FileClient.java        # Console client application
│   ├── SharedState.java       # Synchronized shared resources
│   └── MultiClientTest.java   # Concurrent load test (3 clients)
├── shared/                    # Files available for download
│   ├── notes.txt
│   ├── hello.txt
│   ├── course.pdf
│   └── binary.dat
├── downloads/                 # Files downloaded by the client
└── README.md

How It Works

The server listens on port 12346 using a ServerSocket. For each incoming connection, a new Thread running a ClientHandler instance is created. All threads share a single SharedState object, which tracks connected clients, logs operations, and counts downloads — all protected with synchronized methods.

Communication Protocol

Command	Description	Server Response
LIST	Request the list of available files	File names, one per line
GET <filename>	Download a file	File size (long) + raw bytes
QUIT	Disconnect cleanly	Connection closed

Architecture

Getting Started

Prerequisites

• Java 11 or higher
• IntelliJ IDEA (recommended) or any Java IDE

1. Clone the repository:

git clone https://github.com/m-belefqih/MultiThreaded-File-Server.git
cd MultiThreaded-File-Server

2. Run the Server

# Compile
javac -d out/production/MultiThreaded-File-Server/*.java
 
# Start the server
java -cp out/production/MultiThreaded-File-Server FileServer

Expected output:

File server started on port 12346...
Waiting for clients...

3. Run a Client

Open a new terminal and run:

java -cp out/production/MultiThreaded-File-Server FileClient

Expected output:

Connected to file server successfully.
################ Commands ################
# LIST:           List available files   #
# GET <filename>: Download a file        #
# QUIT:           Disconnect from server #
##########################################
Enter your commands:
>

Example Session

> LIST
--- Files on Server ---
notes.txt
hello.txt
course.pdf
binary.dat
-----------------------
 
> GET course.pdf
Downloading course.pdf (102400 bytes)...
Download complete: downloads/course.pdf
 
> QUIT
Closing connection.

📸 Demo — 3 Simultaneous Clients

The screenshot below shows the system running with 1 server + 3 clients connected simultaneously, demonstrating concurrent file downloads and real-time server statistics.

What the screenshot shows:

• Top-left — Server console: 3 clients connected, live stats updated automatically
• Top-right — Client 1: LIST → GET notes.txt ✅ → GET test.pdf ❌ (not found)
• Bottom-left — Client 2: LIST → GET binary.dat ✅
• Bottom-right — Client 3: LIST → QUIT ✅