Table of Contents

• Spring Kafka Project
  • Introduction
• Consumer Application
  • Consumer Configuration Overview
    • Listening to Kafka Topics
    • Consumer Factory Configurations
    • ConcurrentKafkaListenerContainerFactory
• Producer Application
  • Overview
  • Key Components
    • LibraryEventProducer
    • Producer Interface
• Domain
  • LibraryEvent
  • Book
• Setup and Configuration
  • Docker Compose

Spring Kafka Project

This project is a demo for learning about Spring for Apache Kafka.

Consumer

Located under consumer/, this service is a Spring Boot application that listens to Kafka topics and processes incoming messages.

Consumer Configuration Overview

The ConsumerConfig class is a @Configuration bean, annotated also with @EnableKafka. The @EnableKafka enables spring's application context to register the consumers annotated with the @KafkaListener annotation:

   public static final String LIBRARY_EVENTS = "library-events";

   @KafkaListener(topics = {LIBRARY_EVENTS})
   @Override
   public void consume(ConsumerRecord<Integer, String> consumerRecord) throws JsonProcessingException, MyRetriableException {

      LibraryEvent libraryEvent = new ObjectMapper().readValue(consumerRecord.value(), LibraryEvent.class);
      if (libraryEvent.getLibraryEventId() == null)
         throw new IllegalArgumentException(LIBRARY_EVENT_ID_CANNOT_BE_NULL);
      else if (libraryEvent.getLibraryEventId() == 0)
         throw new MyRetriableException(LIBRARY_EVENT_ID_0);
      log.info("Consumer Record: {}", consumerRecord);
   }

Consumer Factory Configurations

The following configurations are specified in the application.properties file.

• Bootstrap Servers: kafka:29092 - The Kafka broker addresses.
• Key Deserializer: org.apache.kafka.common.serialization.IntegerDeserializer - Deserializer for the key that is used when consuming messages.
• Value Deserializer: org.apache.kafka.common.serialization.StringDeserializer - Deserializer for the value that is used when consuming messages.
• Group ID: library-events-listener-group

This method defines a ConcurrentKafkaListenerContainerFactory bean that configures the Kafka listener containers and allows the creation of multiple concurrent consumer threads for each @KafkaListener

@Bean
public ConcurrentKafkaListenerContainerFactory<Integer, String> kafkaListenerContainerFactory(ConsumerFactory<Integer, String> consumerFactory) {
    ConcurrentKafkaListenerContainerFactory<Integer, String> factory = new ConcurrentKafkaListenerContainerFactory<>();
    factory.setConsumerFactory(consumerFactory);
    factory.setCommonErrorHandler(errorHandler());
    return factory;
}

Producer Application

Found in producer/, the Producer Application serves as a Kafka message producer. It publishes library event messages to Kafka topics, handling serialization and response handling through callbacks. Key components include:

• LibraryEventProducer: Sends library events to Kafka, implementing error handling and successful message callbacks.
• Producer: Defines the generic producer interface, encapsulating the production of messages.

Domain

Both applications share a common domain context with two primary entities:

• LibraryEvent: Represents an event in the library, containing identifiers and associated book details.
• Book: Contains book details like ID, name, and author.

Setup and Configuration

Check the docker-compose file in the root project and start from there to build & run