💬 Real-Time Room Chat Application

This repository contains the backend implementation for a scalable, room-based chat application demonstrating advanced Spring Boot features, including WebSockets and MongoDB persistence.

🚀 Key Technologies

• Framework: Spring Boot 4.0.0 (Java)
• Database: MongoDB (using Spring Data MongoDB for persistence)
• Real-time Protocol: WebSocket using STOMP (Simple Text Oriented Messaging Protocol)
• Messaging: Spring's SimpMessagingTemplate for programmatic message broadcasting.

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⚙️ Backend Architecture and Components

The application is built around three core layers: Configuration, Persistence, and Real-time Communication.

1. 🌐 WebSocket & STOMP Configuration (WebSocketConfig)

This class establishes the plumbing for real-time communication.

• Native WebSocket Endpoint: Defines the entry point for native WebSocket clients (like Postman or other servers).
  • Connection URL: ws://localhost:8080/ws-chat
• Message Broker: Configures the in-memory broker used for broadcasting messages.
  • Broker Prefix: /topic (e.g., messages are broadcast to /topic/room/{id}).
• Application Prefix: Designates the path for messages intended for Java application logic.
  • Application Prefix: /app (e.g., client sends messages to /app/sendMessage/{id}).

2. 🗄️ Persistence Layer (MongoDB)

This layer manages the permanent storage of room and message data.

• Spring Data MongoDB: Used to abstract database interaction.
• Repository Pattern: A standard Spring Data Repository interface is used (e.g., RoomRepository) which provides methods like findByRoomId() and save().
• Data Integrity: The Message objects are stored as embedded documents within the main Room document, demonstrating a practical MongoDB data model for chat persistence.

3. 🎯 Controller & Message Handling (ChatController)

This is the core business logic layer where incoming messages are processed.

Component	Annotation/Method	Function
Routing	@MessageMapping("/sendMessage/{roomId}")	Maps incoming STOMP SEND frames (from /app) to this Java method.
Variable Extraction	@DestinationVariable String roomId	Extracts the dynamic room ID from the message destination URL for use in database lookups.
Persistence	roomRepository.save(room)	Updates the room document in MongoDB with the new message record.
Broadcasting	messagingTemplate.convertAndSend()	Manually sends the saved Message object to the correct broker destination (/topic/room/{roomId}). This ensures persistence completes before broadcasting.

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🧪 Testing the API (Postman STOMP Guide)

To test the full server pipeline, use the native WebSocket endpoint (/ws-chat). A Room with ID 123 must exist in your MongoDB for this test to succeed.

Step 1: Establish Connection

Connect to the native endpoint: ws://localhost:8080/ws-chat

Step 2: Subscribe (Listen)

Send the SUBSCRIBE frame to the broker channel:

SUBSCRIBE
id:sub-1
destination:/topic/room/123
ack:auto


^@

Send the SEND frame to the application handler to trigger the save and broadcast logic:

SEND
destination:/app/sendMessage/123
content-type:application/json

{"roomId": "123", "content": "Test message from API", "sender": "Postman Tester"}
^@