Spring Boot SSE Example

A demonstration of Server-Sent Events (SSE) implementation using Spring Boot, showcasing real-time event streaming to web clients.

Features

• Real-time Event Streaming: Server-sent events via HTTP SSE protocol
• Multiple Event Types: Heartbeat, notifications, and custom events
• Concurrent Connections: Thread-safe handling of multiple SSE clients
• Interactive Web Client: HTML test interface for SSE demonstration
• Hot Reload: Spring Boot DevTools for development efficiency

Quick Start

Prerequisites

• Java 17 or higher
• No additional installation required (uses Gradle wrapper)

Running the Application

1. Clone and navigate to the project directory
2. Start the application:

   ./gradlew bootRun

3. Open your browser to http://localhost:8080/test.html

API Endpoints

SSE Stream

GET /api/events
Content-Type: text/event-stream

Establishes an SSE connection and streams real-time events.

Trigger Custom Event

POST /api/trigger-event
Content-Type: application/json
Body: "Your custom message"

Broadcasts a custom event to all connected SSE clients.

Health Check

GET /api/

Returns server status message.

Event Types

• connected: Sent when a client first connects
• heartbeat: Periodic server heartbeat (every 30 seconds)
• notification: Sample notifications (every 15 seconds)
• custom: User-triggered events via POST endpoint

Testing

Command Line Testing

# Stream SSE events (press Ctrl+C to stop)
curl -N http://localhost:8080/api/events

# Send custom event
curl -X POST -H "Content-Type: application/json" \
     -d '"Hello from curl!"' \
     http://localhost:8080/api/trigger-event

Web Interface Testing

Visit http://localhost:8080/test.html for an interactive web interface that demonstrates:

• Connecting/disconnecting from SSE stream
• Real-time event display
• Sending custom events

Architecture

┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
│   Web Client    │────│ EventController │────│  EventService   │
│                 │    │                 │    │                 │
│ EventSource API │◄───│ SseEmitter      │◄───│ Periodic Tasks  │
└─────────────────┘    └─────────────────┘    └─────────────────┘

• EventController: REST endpoints for SSE and event triggering
• EventService: Connection management and event broadcasting
• SseEmitter: Spring's SSE implementation for streaming events

Development

Build Commands

./gradlew build          # Build the application
./gradlew test           # Run tests
./gradlew bootRun        # Run development server

Configuration

• Port: 8080 (configurable in application.properties)
• CORS: Enabled for all origins (development mode)
• DevTools: Automatic restart and live reload enabled

Use Cases

This example demonstrates SSE patterns suitable for:

• Real-time notifications
• Live dashboards
• Chat applications
• System monitoring displays
• Live data feeds

License

This project is provided as an educational example.