Problem Statement 1: Implement Publisher Subscriber Notification System

This project implements a publisher-subscriber notification system using Java and Spring Boot. It allows subscribers to subscribe to topics, receive notifications for subscribed topics, and unsubscribe from topics.

Live Link: https://publishersubscriber.onrender.com/api

Note : The first request to this URL might take up to 50 seconds to respond. This is because I am using a free instance that automatically shuts down after a period of inactivity.
However, after the first request is completed, all subsequent requests will respond normally.

Setup

1. Clone the repository:

git clone https://github.com/AryanP45/PublisherSubscriber.git

2. Open the project in your preferred Java IDE. (IntelliJ IDEA)

3. Build the project using Maven.

API Documentation

Postman Collection: Link to API Collection

The system provides the following APIs:

1. Subscribe

This API allows subscribers to subscribe to a topic.
Note: Creates a new topic if it doesn't exist.

• Endpoint: POST /api/subscribe
  Try with live link: https://publishersubscriber.onrender.com/api/subscribe
• Request Body:

  {
    "topicId": "string",
    "subscriberId": "string"
  }

• Responses:
  • 200 OK: Successfully subscribed.
  • 409 Conflict: Subscriber already subscribed to the topic.
  • 500 Internal Server Error: Error occurred while subscribing.

2. Notify

This API sends notifications to all subscribers of a particular topic.

• Endpoint: GET /api/notify
  Try with live link: https://publishersubscriber.onrender.com/api/notify
• Query Parameters:
  • topicId: The ID of the topic to notify subscribers.
• Responses:
  • 200 OK: Successfully notified subscribers.
  • 404 Not Found: No subscribers have subscribed to the topic or topic not found.
  • 500 Internal Server Error: Error occurred while notifying.

3. Unsubscribe

This API allows subscribers to unsubscribe from a topic.

• Endpoint: POST /api/unsubscribe
  Try with live link: https://publishersubscriber.onrender.com/api/unsubscribe
• Request Body:

  {
    "topicId": "string",
    "subscriberId": "string"
  }

• Responses:
  • 200 OK: Successfully unsubscribed.
  • 404 Not Found: Topic or subscriber not found.
  • 500 Internal Server Error: Error occurred while unsubscribing.

4. Get All Topics and Subscribers

This API retrieves all topics along with their subscribers.

• Endpoint: GET /api/all
  Try with live link: https://publishersubscriber.onrender.com/api/all
• Responses:
  • 200 OK: Successfully retrieved all topics with subscribers.

Driver Function

A driver function has been implemented to demonstrate the flow of the application. Below is a simple example:

public class Driver {

    public static void main(String[] args) {
        NotificationService notificationService = new NotificationService();

        // Subscribe
        String subscribeResult = notificationService.subscribe("topic1", "subscriber1");
        System.out.println("Subscribe Result: " + subscribeResult);

        // Notify
        String notifyResult = notificationService.notify("topic1");
        System.out.println("Notify Result: " + notifyResult);

        // Unsubscribe
        String unsubscribeResult = notificationService.unsubscribe("topic1", "subscriber1");
        System.out.println("Unsubscribe Result: " + unsubscribeResult);
    }
}

output:

Subscribe Result: subscribed Successfully
Notification sent to subscriber with ID : subscriber1
Notify Result: Notified 1 Subscribers
Unsubscribe Result: Unsubscribed

Edge Cases

• Null topic ID or subscriber ID is handled in all APIs.
• API responses provide appropriate error messages for edge cases such as subscriber already subscribed, topic not found, etc.
• Unit tests have been implemented to cover various scenarios, including edge cases.

Contributors

• Aryan Patil (@aryanp45)

If any query, contact: aryanitinpatil@gmail.com