⚙️ The backend implements a real-time chat system using Spring Boot + WebSockets (STOMP) + REST APIs + JPA.

Messages can include text or files, support read/unread status, and are persisted in the database.

This is the backend for a real-time chat application.
It’s built with Spring Boot and provides secure APIs and WebSocket connections for instant communication. The backend takes care of authentication, message delivery, and storing chat history so the frontend (React + TailwindCSS) can focus on the user experience.

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✨ What this backend does

• Handles real-time messaging through WebSockets with <200ms latency
• Provides REST APIs for authentication, user management, and sessions
• Uses JWT tokens for secure login and multi-device access
• Stores messages and sessions in a PostgreSQL database
• Scales to support thousands of concurrent users
• Works seamlessly with the React frontend (separate repo)

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🛠 Tech Stack

• Spring Boot (REST + WebSocket)
• PostgreSQL for persistence
• JWT for authentication
• Maven for dependency management
• Docker for containerization
• Render / AWS for deployment

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1. Message Entity

Represents a chat message stored in the database.

Fields

• id → Primary key (auto-generated).

• sender → User who sends the message.

• recipient → User who receives the message (nullable for public messages).

• content → Text content of the message.

• fileName → Optional file name if a file is attached.

• timestamp → Time the message was sent.

• messageType → Enum (TEXT, IMAGE, FILE, etc.).

• isRead → Whether recipient has read the message.

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2. MessageController

Provides both REST endpoints and WebSocket endpoints for chat.

Method	Endpoint	Description
GET	/api/messages/history/{userId}/{user2Id}	Get chat history between two users.
DELETE	/api/messages/history/{user1Id}/{user2Id}	Clear chat history between two users.
DELETE	/api/messages/{messageId}	Delete a single message (only by sender).

WebSocket Endpoints

• /app/chat.send → Send message (STOMP).

• /app/chat.typing → Send typing indicator.

WebSocket Subscriptions

/user/{userId}/queue/messages → Private user queue for receiving messages.

/user/{userId}/queue/typing → Private queue for typing status.

/topic/chat → Public chat broadcast.

/topic/delete → Notify clients when a message is deleted.

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3. MessageService

Business logic for handling chat.

Key Methods:

• saveMessage(Message msg) → Saves a new message to DB.

• deleteMessage(Long messageId, Long userId) → Deletes a message if current user is sender.

• clearChatHistory(Long user1Id, Long user2Id) → Deletes all messages between two users.

• userCanAccessMessage(Long messageId, Long userId) → Verifies if user can access a message.

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4. Messaging Flow

Sending a Message

User sends message via WebSocket → /app/chat.send.

MessageController builds a Message object and persists it.

Saved message is mapped into a MessageDTO (with generated ID).

Message is delivered to:

Recipient’s private queue → /user/{recipientId}/queue/messages.

Sender’s own queue → /user/{senderId}/queue/messages.

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Receiving Messages

Clients subscribe to /user/{id}/queue/messages to receive private messages.

Clients subscribe to /topic/chat for public messages.

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Typing Indicator

Client sends typing status via /app/chat.typing.

Recipient receives it on /user/{recipientId}/queue/typing.

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Deleting a Message

Sender issues DELETE : /api/messages/{messageId}.

MessageService verifies ownership.

If deleted → backend broadcasts /topic/delete with {id: messageId} so UIs can remove it in real-time.

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5. User Entity

Represents a chat message stored in the database.

Fields:

• id → Primary key (auto-generated).

• username → Unique username for login and display.

• email → Unique email address.

• password → Hashed password (nullable for OAuth users).

• role → Role of the user (e.g., USER, ADMIN).

• googleId → Optional field for Google OAuth authentication.

• createdAt → Date when the user was registered.

• updatedAt → Date of the last profile update.

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5. User Controller

Method	Endpoint	Description
GET	/api/users/{id}	Get user by ID.
GET	/api/users/username/{username}	Get user by username.
GET	/api/users/email/{email}	Get user by email.
GET	/api/users/search?username={username}	Search users by username (case-insensitive).
POST	/api/users/register	Register a new user.
POST	/api/users/oauth/google	Register/Login user via Google OAuth.
PUT	/api/users/{id}	Update user details.
DELETE	/api/users/{id}	Delete user account.

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6. User Service

Contains the business logic for user management.

Key Methods

• loadUserByUsername(String username) → Loads a user for authentication (used by Spring Security).

• getUserIdByUsername(String username) → Retrieves user ID by username.

• registerUser(User user) → Registers a new user with validation.

• findByEmail(String email) → Finds user by email.

• findByUsername(String username) → Finds user by username.

• findByGoogleId(String googleId) → Finds user registered via Google.

• updateUser(Long id, User user) → Updates existing user details.

• deleteUser(Long id) → Deletes a user account.

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🚀 Getting Started

Clone the repo and build the project:

git clone https://github.com/your-username/realtime-chat-backend.git
cd realtime-chat-backend
./mvnw clean install