Java Chat Room — CSC-1004 Course Project

A multithreaded console chat room implemented in Java using Socket programming. This project is submitted as part of CSC-1004: Computational Laboratory Using Java, The Chinese University of Hong Kong, Shenzhen (CUHK-SZ).

Course context: the assignment requires a Java chat room with multithreading, chat-room functions, chat-record storage, and proper message display. 3

Features

• TCP client–server architecture on localhost:6666
• Automatic 5-digit client ID assignment (e.g. 01234)
• Custom username input during handshake
• Real-time broadcasting to all connected clients
• Separate sender/receiver threads on the client side
• Server-side multithreading: one ClientHandler per connection
• Online user list sent to newly joined clients
• Join/leave system notifications for all users
• Timestamped messages (HH:mm:ss)
• Server-side chat history persisted to chat_history.txt
• Recent history delivered to new clients (last 50 messages)
• Client /save command exports chat history to desktop
• Commands: /help, /exit, /save (client); /users, /history (server-side)

Tech Stack

• Java SE (Sockets, DataInputStream/DataOutputStream, Threads)
• Vector for thread-safe active client storage
• AtomicInteger for unique ID generation
• File I/O for history persistence

Project Structure

src/main/java/org/example/ ├── Main.java # Launcher: choose 1=Server, 2=Client ├── Server.java # ServerSocket, broadcast, history, ClientHandler ├── Client.java # Console client, sender/receiver threads, /save pom.xml # Maven project file chat_history.txt # Auto-created server-side history file

Requirements

• JDK 11+ (JDK 17/21 recommended)
• Maven (optional) or any Java IDE

Run with Maven

Terminal 1 - start server

mvn exec:java -Dexec.mainClass=org.example.Main

choose 1

Terminal 2/3/... - start clients

mvn exec:java -Dexec.mainClass=org.example.Main

choose 2

Run with plain javac

Compile

javac src/main/java/org/example/*.java -d out

Server terminal

java -cp out org.example.Main

choose 1

Client terminal(s)

java -cp out org.example.Main

choose 2

Usage

1. Start the server first.
2. Start one or more clients.
3. Enter a username when prompted.
4. Chat normally; messages are broadcast with timestamps.
5. Client commands:
   • /save save chat history to desktop as my_chat_history.txt
   • /help show command list
   • /exit leave the chat room
6. Server-side client commands:
   • /users list online users
   • /history show recent server history

Notes for CSC-1004

• Multithreading: server spawns one thread per client; client uses one receiver thread + main sender thread.
• Socket I/O: ServerSocket/Socket with DataInputStream/DataOutputStream.
• Storage: in-memory history plus append-only chat_history.txt.
• Suitable for local multi-client demonstration and video recording.

Repository: https://github.com/berserkross/Java_Chat_Room