🌐 Java TCP/IP Concurrent Servers

A backend Java project featuring a suite of three TCP/IP server applications, demonstrating progression in socket programming, multi-threading, and remote file management.

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🎯 Project Overview

This project focuses on building robust client-server architectures using Java. The main objective is to handle multiple client connections simultaneously without blocking the main server thread, ensuring a smooth and responsive network application. The repository includes three distinct server programs, culminating in a fully functional remote file server with state-based authentication.

🛠️ Programs Included

The repository is structured around three server implementations, each adding a layer of complexity:

1. Basic Concurrent Server

• Foundation: Upgrades a standard sequential server to a concurrent architecture.
• Thread-per-client: Uses Java's Thread class and Runnable interfaces to spawn a new thread for every incoming connection, allowing multiple clients to interact with the server simultaneously without bottlenecks.

2. Advanced Command Server

• Complex I/O: Builds upon the basic concurrent model to handle more complex data processing and continuous client-server message exchange.
• Resource Management: Ensures sockets and streams are properly managed and closed across multiple active threads to prevent resource leaks.

3. Authenticated Remote File Server

• Authentication System: The flagship implementation. The server requires a valid username and password session (e.g., javier / secreta) before granting access to its features.
• State Machine Logic: Operates on a strict state diagram (Waiting for Connection -> Authenticating -> Ready for Commands -> Disconnected) to ensure secure request handling.
• Remote File System Access: Once authenticated, clients can interact with the server's filesystem to:
  • List: View the contents of the server's current directory.
  • Read: Request and display the contents of a specific file over the network.
  • Exit: Gracefully terminate the session.

⚙️ How to Compile & Run

1. Clone the repository:

   git clone [https://github.com/carlopezc/Java-Concurrent-Servers.git](https://github.com/carlopezc/Java-Concurrent-Servers.git)
   cd Java-Concurrent-Servers

2. Compile the .java files (replace program3 with the actual folder name):

   javac src/program3/*.java

3. Start the Server in one terminal:

   java -cp src program3.ServerMain

4. Start one or more Clients in separate terminals to test concurrency:

   java -cp src program3.ClientMain