🚀 Learning Apache Kafka

A hands-on Spring Boot project for learning Apache Kafka — covering producers, consumers, custom serialization, and REST-based message publishing.

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📖 About

This project is a practical learning resource for integrating Apache Kafka with Spring Boot. It demonstrates how to configure a Kafka producer and consumer from scratch, serialize/deserialize custom Java objects using JSON, and expose a REST API to publish messages to a Kafka topic.

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✨ Features

• ⚙️ Custom Kafka Producer — Configured with KafkaTemplate and JsonSerializer for sending custom Message objects
• 👂 Kafka Consumer / Listener — Uses @KafkaListener with ConcurrentKafkaListenerContainerFactory to consume messages from a topic
• 🔄 JSON Serialization — Custom objects serialized/deserialized using Spring Kafka's JsonSerializer & JsonDeserializer
• 🌐 REST API — POST /api/v1/messages endpoint to publish messages to the syscomz Kafka topic
• 🏃 CommandLineRunner — On startup, automatically sends 100 test messages to Kafka to verify the setup
• 🔧 Trusted Package Configuration — Consumer factory explicitly trusts com.syscomz for safe deserialization

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🗂️ Project Structure

learning-apache-kafka/
├── src/
│   └── main/
│       ├── java/com/syscomz/
│       │   ├── KafkaApplication.java        # Entry point + CommandLineRunner (sends 100 messages on startup)
│       │   ├── KafkaListeners.java          # @KafkaListener consumer for the "syscomz" topic
│       │   ├── Message.java                 # Custom message record/model
│       │   ├── MessageController.java       # REST controller — POST /api/v1/messages
│       │   ├── MessageRequest.java          # Request DTO
│       │   └── config/
│       │       ├── KafkaProducerConfig.java # Producer factory + KafkaTemplate bean
│       │       └── KafkaConsumerConfig.java # Consumer factory + listener container factory
│       └── resources/
│           └── application.properties       # Kafka bootstrap server config
├── pom.xml
└── README.md

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🛠️ Tech Stack

Technology	Version	Purpose
Java	17	Programming Language
Spring Boot	3.0.3	Application Framework
Spring Web	2.7.6	REST API
Spring Kafka	3.0.3	Kafka Integration
Apache Maven	Latest	Build Tool

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⚡ Getting Started

Prerequisites

• ☕ Java 17+
• 🐳 Docker (recommended for running Kafka locally)
• 📦 Apache Maven or use the included mvnw wrapper

1. Start Apache Kafka

The easiest way is via Docker:

docker run -d --name kafka \
  -p 9092:9092 \
  -e KAFKA_CFG_ZOOKEEPER_CONNECT=zookeeper:2181 \
  bitnami/kafka:latest

Or use a docker-compose.yml with Zookeeper + Kafka.

2. Clone the Repository

git clone https://github.com/bdostumski/learning-apache-kafka.git
cd learning-apache-kafka

3. Run the Application

./mvnw spring-boot:run

On startup, CommandLineRunner will automatically send 100 messages to the syscomz topic. Watch the console for consumer output:

Listener received data: Hello kafka 0 :)
Listener received data: Hello kafka 1 :)
...

4. Publish a Message via REST

curl -X POST http://localhost:8080/api/v1/messages \
  -H "Content-Type: application/json" \
  -d '{"message": "Hello from REST!"}'

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🔌 API Reference

Method	Endpoint	Description	Body
POST	/api/v1/messages	Publish a message to Kafka	{ "message": "your text" }

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⚙️ Configuration

Property	Default	Description
spring.kafka.bootstrap-servers	localhost:9092	Kafka broker address

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📚 Key Concepts Explored

• Kafka Topics — Messages are published to and consumed from the syscomz topic
• Producer Configuration — ProducerFactory with StringSerializer (key) + JsonSerializer (value)
• Consumer Configuration — ConsumerFactory with StringDeserializer + JsonDeserializer with trusted packages
• Listener Container Factory — ConcurrentKafkaListenerContainerFactory for concurrent message processing
• Custom Object Messaging — Sending and receiving a custom Message record with a timestamp

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📄 License

This project is open source and available for learning purposes.

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Made with ❤️ for learning Apache Kafka with Spring Boot