boot-r2dbc-notify-listen

Spring Boot R2DBC Notify/Listen Example

This project demonstrates how to implement PostgreSQL's NOTIFY/LISTEN feature using Spring Boot and R2DBC. It showcases real-time notifications between database and application using PostgreSQL's pub/sub capabilities.

---

Features

• Reactive PostgreSQL connectivity using R2DBC
• Implementation of PostgreSQL NOTIFY/LISTEN mechanism
• Real-time event notifications
• Reactive endpoints for publishing and receiving notifications

---

Prerequisites

• JDK 21
• Maven
• Docker and Docker Compose
• PostgreSQL (or use provided Docker Compose)

---

Getting Started

1. Start PostgreSQL using Docker Compose:

   docker-compose up -d

2. Build the application:

   ./mvnw clean package

3. Run the application:

   ./mvnw spring-boot:run

---

Architecture

sequenceDiagram
    participant Client
    participant Application
    participant Listener
    participant PostgreSQL

    Note over Application: Application starts
    Application->>PostgreSQL: Connect to database
    Application->>PostgreSQL: LISTEN channel_name
    
    Note over Client: Trigger notification
    Client->>Application: POST /api/notify
    Application->>PostgreSQL: NOTIFY channel_name, 'message'
    PostgreSQL-->>Listener: Notification event
    Listener-->>Application: Process notification
    Application-->>Client: Notification processed

    Note over Client: Subscribe to events
    Client->>Application: WebSocket connection
    Application-->>Client: Stream notifications

Loading

---

Usage

1. To publish a notification:

   curl -X POST http://localhost:8080/api/notify \
        -H "Content-Type: application/json" \
        -d '{"channel": "events", "message": "Hello World!"}'

2. To subscribe to notifications:

   • Connect to WebSocket endpoint: ws://localhost:8080/notifications
   • Or use Server-Sent Events endpoint: http://localhost:8080/notifications/sse

---

Configuration

Key configuration properties in application.properties:

# R2DBC PostgreSQL Configuration
spring.r2dbc.url=r2dbc:postgresql://localhost:5432/postgres
spring.r2dbc.username=postgres
spring.r2dbc.password=postgres

# Notification Channel Configuration
app.notification.channel=events

---

How It Works

1. The application establishes a connection to PostgreSQL using R2DBC
2. It sets up LISTEN on specified channels
3. When a notification is published:
   • Application executes NOTIFY command
   • PostgreSQL broadcasts to all listeners
   • Listeners receive and process notifications
4. Connected clients receive notifications via WebSocket/SSE

---

Contributing

Feel free to submit issues and enhancement requests!