Concurrent P2P Image Sharing (Java)

Coursework project for Concurrent Programming (UCM), 2024–2025. A client–server directory plus peer-to-peer (P2P) image transfer system built with Java, TCP sockets, and a Swing GUI.

Authors

• Alejandro Parreño Minaya — @aparreno14
• Diego Ostos Arellano

What this project does

• Clients connect to a central server to register and publish a list of available images.
• When a client requests an image, the server matches requester ↔ owner.
• The actual file is transferred directly between clients (P2P) over TCP.

Architecture (high level)

Server (directory / broker)

• Listens on a fixed TCP port (see src/server/Server.java).

• Maintains:

  • active users and their published image lists
  • input/output streams per user

• Spawns dedicated listener threads to handle multiple clients concurrently.

• Provides a Swing GUI to display connected users and server logs.

Client

• Swing GUI client.

• Talks to the server for:

  • registration
  • listing available images
  • requesting an image

• For P2P transfers:

  • Emitter opens a temporary TCP port and serves the requested file to the peer.
  • Receiver connects to that temporary port and downloads the image.

Message protocol (overview)

The system uses a custom message protocol (serializable objects) with message kinds such as:

• CONEXION / CONF_CONEXION
• LISTA_PRODUCTOS / CONF_LISTA_PRODUCTOS
• PEDIR
• EMITIR
• PREPARADO_CS → server (emitter announces P2P port)
• PREPARADO_SC → requester (server forwards P2P port)
• IMAGEN_NO_EXISTE
• CERRAR_CONEXION / CONF_CERRAR_CONEXION

Data folders (important)

This project expects local folders under data/:

• Images you want to share should be placed under: data/<userId>/
• Downloaded images are saved under: data/<userId>/descargas/

Tip: create those folders for each user you test with.

How to run (Eclipse recommended)

This project was developed with Windows + Eclipse.

1. Import the project in Eclipse (existing project from filesystem).

2. Run the server:

   • Run src/server/Launcher.java (starts the GUI + server loop).

3. Run two clients (in separate runs):

   • Run src/cliente/Cliente.java twice.

4. Use the GUI to:

   • connect/register with different userIds
   • publish images (by placing files in data/<userId>/)
   • request an image from the global list and download it via P2P

Notes:

• Local testing assumes localhost.
• Make sure your firewall allows local TCP connections (server port + temporary P2P ports).

Repository structure

• src/server/ — server logic + GUI
• src/cliente/ — client GUI + P2P emitter/receiver threads
• src/mensajes/ — message classes and enums
• src/tablas/ — shared tables (users/streams/products) with concurrency control
• src/semaforos/, src/locks/ — synchronization primitives used by the tables

License

GPL — see LICENSE.

Disclaimer

This is an educational project developed for a university course.