Pull Request

What does this PR do?

This PR introduces a microservice-based architecture that includes a polling-publisher and a subscriber-service communicating via Apache Kafka. It demonstrates an in-memory data flow mechanism using Kafka topics.

The PR includes:

Kafka producer REST endpoint for sending messages
Kafka consumer that listens automatically and processes messages
Spring Boot configuration for both microservices
Initial testing and local setup for message flow validation

Fixes #2673

Type of change

[x] New feature (non-breaking change)
[x] Documentation update

How has this been tested?

Manually tested Kafka message publishing via /send endpoint
Verified automatic listening and processing in subscriber microservice
Logs and terminal output confirm end-to-end communication

Additional context

Both microservices are designed for local Kafka communication using port 9092. Make sure the Kafka broker is running before testing

Jun 01 '25 18:06 quantdevv

PR Summary

This PR introduces a microservice-based architecture using Kafka for communication between a polling publisher and a subscriber service. It includes REST endpoints, Kafka producers and consumers, Spring Boot configurations, and testing for message flow validation.

Changes

File	Summary
`polling-publisher/README.md`	This file provides a comprehensive guide to the Polling Publisher-Subscriber pattern, explaining its intent, architecture, real-world examples, and implementation using Spring Boot and Kafka. It also covers when to use this pattern, its benefits and trade-offs, and related design patterns.
`polling-publisher/etc/polling-publisher.urm.puml`	New file.
`polling-publisher/polling-service/etc/polling-service.urm.puml`	New file.
`polling-publisher/polling-service/pom.xml`	This file configures the Maven project for the polling service microservice, defining dependencies and build settings. It includes Spring Boot, Kafka, and testing dependencies.
`polling-publisher/polling-service/src/main/java/com/iluwatar/polling/App.java`	This is the main application class for the polling service microservice. It uses Spring Boot annotations to enable the application context and scheduling.
`polling-publisher/polling-service/src/main/java/com/iluwatar/polling/DataRepository.java`	This class defines an in-memory repository for storing and retrieving data. It uses a `HashMap` for data storage and provides methods for saving, retrieving, deleting, and finding all data.
`polling-publisher/polling-service/src/main/java/com/iluwatar/polling/DataSourceService.java`	This service is responsible for managing data, including adding, retrieving, and removing data. It uses a `DataRepository` and a scheduler to periodically generate and add new data.
`polling-publisher/polling-service/src/main/java/com/iluwatar/polling/KafkaProducer.java`	This class handles sending messages to Kafka. It uses Spring's `KafkaTemplate` to publish messages to specified topics.
`polling-publisher/polling-service/src/main/java/com/iluwatar/polling/PollingController.java`	This REST controller provides a `/send` endpoint for manually sending messages to Kafka and a health check endpoint.
`polling-publisher/polling-service/src/main/java/com/iluwatar/polling/PollingScheduler.java`	This class schedules the data polling and publishing tasks using Spring's `@Scheduled` annotation. It retrieves data from the `DataSourceService` and sends it to Kafka.
`polling-publisher/polling-service/src/main/resources/application.yml`	This file contains the Spring Boot configuration for the polling service, including Kafka broker settings, consumer group ID, and port number.
`polling-publisher/polling-service/src/test/java/com/iluwatar/polling/AppTest.java`	This file contains a test case to verify the application context loading.
`polling-publisher/polling-service/src/test/java/com/iluwatar/polling/DataRepositoryTest.java`	This test suite verifies the functionality of the `DataRepository` class, including saving, retrieving, deleting, and finding all data.
`polling-publisher/polling-service/src/test/java/com/iluwatar/polling/DataSourceServiceTest.java`	This test suite contains test cases for the `DataSourceService`, covering adding, retrieving, removing, and getting all data.
`polling-publisher/pom.xml`	This is the main pom file for the polling-publisher module. It aggregates the `polling-service` and `subscriber-service` modules and defines common dependencies.
`polling-publisher/subscriber-service/etc/subscriber-service.urm.puml`	New file.
`polling-publisher/subscriber-service/pom.xml`	This file configures the Maven project for the subscriber service microservice, defining dependencies and build settings. It includes Spring Boot, Kafka, and testing dependencies.
`polling-publisher/subscriber-service/src/main/java/com/iluwatar/subscriber/App.java`	This is the main application class for the subscriber service microservice. It uses Spring Boot annotations to enable the application context.
`polling-publisher/subscriber-service/src/main/java/com/iluwatar/subscriber/KafkaConsumer.java`	This class consumes messages from Kafka topics. It uses Spring's `@KafkaListener` annotation to listen for messages on the `updates` and `API` topics.
`polling-publisher/subscriber-service/src/main/resources/application.yml`	This file contains the Spring Boot configuration for the subscriber service, including Kafka broker settings, consumer group ID, and port number.
`polling-publisher/subscriber-service/src/test/java/com/iluwatar/subscriber/AppTest.java`	This file contains a test case to verify the application context loading.
`pom.xml`	The `polling-publisher` module was added to the list of modules.