PostgreSQL Notify and Listen support using reactive spring boot

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.

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Features

• Reactive PostgreSQL connectivity using R2DBC

• Implementation of PostgreSQL NOTIFY/LISTEN mechanism

• Real-time event notifications

• Reactive endpoints for publishing and receiving notifications

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Prerequisites

• JDK 21

• Maven

• Docker and Docker Compose

• PostgreSQL (or use provided Docker Compose)

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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

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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

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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

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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

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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

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Contributing

Feel free to submit issues and enhancement requests!