feat : Implement Notify and Listen Support (#1639)

* feat : Implement Notify and Listen Support

* removes flyway support as it is not necessary

* polish

* implements notification and listener

* remove junk

SUMMARY.md

@@ -43,6 +43,7 @@
 * [r2dbc](r2dbc/README.md)
   * [r2dbc-jooq](r2dbc/boot-jooq-r2dbc-sample/README.md)
   * [PostgreSQL JSON and enum column support](r2dbc/boot-r2dbc-json-column/README.md)
+  * [PostgreSQL Notify and Listen support using reactive spring boot](r2dbc/boot-r2dbc-notify-listen/README.md)
   * [r2dbc-boot](r2dbc/boot-r2dbc-sample/README.md)
   * [reactive-cache](r2dbc/boot-r2dbc-reactive-cache/README.md)
 * [scheduler](scheduler/README.md)

pom.xml

@@ -50,6 +50,7 @@
         <module>jpa/multitenancy/schema</module>
         <module>r2dbc/boot-jooq-r2dbc-sample</module>
         <module>r2dbc/boot-r2dbc-json-column</module>
+        <module>r2dbc/boot-r2dbc-notify-listen</module>
         <module>r2dbc/boot-r2dbc-sample</module>
         <module>r2dbc/boot-r2dbc-reactive-cache</module>
         <module>scheduler/boot-scheduler-jobrunr</module>

r2dbc/boot-r2dbc-notify-listen/.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1,19 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+wrapperVersion=3.3.2
+distributionType=only-script
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.9.9/apache-maven-3.9.9-bin.zip

r2dbc/boot-r2dbc-notify-listen/README.md

@@ -0,0 +1,107 @@
+# 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:
+   ```bash
+   docker-compose up -d
+   ```
+
+2. Build the application:
+   ```bash
+   ./mvnw clean package
+   ```
+
+3. Run the application:
+   ```bash
+   ./mvnw spring-boot:run
+   ```
+---
+## Architecture
+
+```mermaid
+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
+```
+---
+## Usage
+
+1. To publish a notification:
+   ```bash
+   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`:
+
+```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!

r2dbc/boot-r2dbc-notify-listen/docker/docker-compose-app.yml

@@ -0,0 +1,17 @@
+version: '3.8'
+services:
+
+  boot-r2dbc-sample:
+    build: ..
+    ports:
+      - "18080:8080"
+      - "18787:8787"
+    restart: always
+    depends_on:
+      - postgresqldb
+    environment:
+      - SPRING_PROFILES_ACTIVE=docker
+      - SPRING_DATASOURCE_DRIVER_CLASS_NAME=org.postgresql.Driver
+      - SPRING_DATASOURCE_URL=jdbc:postgresql://postgresqldb:5432/appdb
+      - SPRING_DATASOURCE_USERNAME=appuser
+      - SPRING_DATASOURCE_PASSWORD=secret

r2dbc/boot-r2dbc-notify-listen/docker/docker-compose.yml

@@ -0,0 +1,42 @@
+services:
+
+  postgresqldb:
+    image: postgres:17.2-alpine
+    hostname: postgresqldb
+    extra_hosts: [ 'host.docker.internal:host-gateway' ]
+    environment:
+      - POSTGRES_USER=appuser
+      - POSTGRES_PASSWORD=secret
+      - POSTGRES_DB=appdb
+    ports:
+      - "5432:5432"
+    networks:
+      - boot-r2dbc-network
+
+  pgadmin:
+    image: dpage/pgadmin4
+    extra_hosts: [ 'host.docker.internal:host-gateway' ]
+    environment:
+      - [email protected]
+      - PGADMIN_DEFAULT_PASSWORD=admin
+      - PGADMIN_CONFIG_SERVER_MODE=False
+      - PGADMIN_CONFIG_MASTER_PASSWORD_REQUIRED=False
+    ports:
+      - "5050:80"
+    depends_on:
+      postgresqldb:
+        condition: service_started
+    volumes:
+      - ./docker_pgadmin_servers.json:/pgadmin4/servers.json
+    entrypoint:
+      - "/bin/sh"
+      - "-c"
+      - "/bin/echo 'postgresqldb:5432:*:appuser:secret' > /tmp/pgpassfile && chmod 600 /tmp/pgpassfile && /entrypoint.sh"
+    restart: unless-stopped
+    networks:
+      - boot-r2dbc-network
+
+
+networks:
+  boot-r2dbc-network:
+    driver: bridge

r2dbc/boot-r2dbc-notify-listen/docker/docker_pgadmin_servers.json

@@ -0,0 +1,14 @@
+{
+    "Servers": {
+        "1": {
+            "Name": "Docker Compose DB",
+            "Group": "Servers",
+            "Port": 5432,
+            "Username": "appuser",
+            "Host": "postgresqldb",
+            "SSLMode": "prefer",
+            "MaintenanceDB": "appdb",
+            "PassFile": "/tmp/pgpassfile"
+        }
+    }
+}