Messengr

A multi-user TCP chat application built in Java.

Messengr is a real-time chat system with support for multiple chat rooms, private messaging, and admin controls. Built to demonstrate socket programming, multithreading, and client-server architecture in Java.

Features

• Multi-user support — Multiple clients can connect simultaneously
• Chat rooms — Create and join named rooms for organized discussions
• Private messaging — Direct messages between individual users
• Real-time communication — Messages delivered instantly across all clients
• Admin commands — User management (kick, view stats)
• Auto-reconnection — Client automatically reconnects on dropped connections
• Message history — Shows recent messages when joining a room
• Configurable — Server behavior controlled via server.properties

Technical Implementation

Architecture

• Client-Server model using TCP sockets
• Thread-per-client design with an ExecutorService thread pool
• Concurrent data structures (ConcurrentHashMap, AtomicBoolean) for thread safety
• Custom protocol for routing different message types (room messages, private messages, commands, system notifications)

Key Java Concepts

• Socket programming (ServerSocket / Socket)
• Multithreading with ExecutorService
• Concurrent collections
• Resource management with try-with-resources
• Graceful shutdown handling

Getting Started

Prerequisites

• Java 8+

Running the Application

1. Start the server:

mvn clean package
java -cp target/messengr.jar com.rednetty.messengr.server.Server

2. Connect a client (in a new terminal):

java -cp target/messengr.jar com.rednetty.messengr.client.ClientApp

3. Connect additional clients by opening more terminals and repeating step 2.

Configuration

Edit src/main/resources/server.properties to adjust server settings:

server.port=7234
server.max_clients=100
security.admin_password=${ADMIN_PASSWORD:changeme}

Set the ADMIN_PASSWORD environment variable before starting the server to configure the admin password securely.

Chat Commands

Command	Description
/help	Show available commands
/users	List users in current room
/rooms	List all available rooms
/join <room>	Join a room
/create <room>	Create a new room
/msg <user> <message>	Send a private message
/status	Show connection status
/quit	Exit

Admin commands (require server password):

Command	Description
/kick <user>	Remove a user from the server
/stats	View server statistics

Project Structure

src/main/java/com/rednetty/messengr/
├── client/
│   └── ClientApp.java      # Terminal-based chat client
├── server/
│   ├── Server.java         # Main server (accepts connections, manages rooms/users)
│   ├── ClientHandler.java  # Per-client thread: reads/routes messages
│   ├── ChatRoom.java       # Room state and broadcast logic
│   └── ChatMessage.java    # Message data model
└── shared/
    └── User.java           # Shared user model

Known Limitations

• Server runs on localhost; remote connections require firewall configuration
• No persistent message storage (history is in-memory only)
• Basic authentication (password-based admin access)

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Built as a deep dive into concurrent network programming in Java.