Kafka Chat Application (Spring Boot Backend)

This is a backend-only chat application built using Spring Boot and Apache Kafka (KRaft mode). The application allows sending and receiving chat messages via REST API endpoints.

Kafka is run using Docker.

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Features

• Send messages to a Kafka topic.
• Consume messages from the Kafka topic.
• Fully backend-driven (REST APIs only).
• Works with Kafka in KRaft mode (no Zookeeper needed).
• Uses JSON serialization for messages.

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Tech Stack

• Java 17+
• Spring Boot
• Apache Kafka (KRaft mode)
• Docker (for Kafka broker)
• Maven (for dependency management)

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Project Structure

src/
└── main/
    └── java/
        └── org/
            └── example/
                └── chatapplication/
                    ├── config/
                    │   └── KafkaConfig.java
                    ├── controller/
                    │   └── ChatController.java
                    ├── producer/
                    │   └── ChatProducer.java
                    ├── consumer/
                    │   └── ChatConsumer.java
                    └── model/
                        └── Messages.java

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Setup Instructions

1. Clone the repository

git clone https://github.com/TornovDutta/ChatApplication.git
cd ChatApplication

2. Start Kafka using Docker

docker-compose up -d

3. Start Spring Boot backend

mvn spring-boot:run

4. Test the REST API

• Send messages
• View consumed messages

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Docker Compose for Kafka (KRaft Mode)

version: '3.8'

services:
  kafka:
    image: apache/kafka:4.0.1
    container_name: kafka
    environment:
      KAFKA_PROCESS_ROLES: broker,controller
      KAFKA_NODE_ID: 1
      KAFKA_LISTENERS: PLAINTEXT://:9092,CONTROLLER://:9093
      KAFKA_ADVERTISED_LISTENERS: PLAINTEXT://localhost:9092
      KAFKA_CONTROLLER_QUORUM_VOTERS: 1@localhost:9093
      KAFKA_CONTROLLER_LISTENER_NAMES: CONTROLLER
      KAFKA_LOG_DIRS: /var/lib/kafka/data
      KAFKA_AUTO_CREATE_TOPICS_ENABLE: 'true'
      KAFKA_OFFSETS_TOPIC_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_REPLICATION_FACTOR: 1
      KAFKA_TRANSACTION_STATE_LOG_MIN_ISR: 1
      CLUSTER_ID: MkU3OEVBNTcwNTJENDM2Qk
    ports:
      - "9092:9092"
    volumes:
      - kafka_data:/var/lib/kafka/data

volumes:
  kafka_data:

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Application Properties (application.properties)

spring.application.name=chat-application
server.port=8080

spring.kafka.bootstrap-servers=localhost:9092

# Producer
spring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.StringSerializer
spring.kafka.producer.value-serializer=org.springframework.kafka.support.serializer.JsonSerializer
spring.kafka.producer.acks=all

# Consumer
spring.kafka.consumer.group-id=chat-group
spring.kafka.consumer.auto-offset-reset=earliest
spring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.StringDeserializer
spring.kafka.consumer.value-deserializer=org.springframework.kafka.support.serializer.JsonDeserializer
spring.kafka.consumer.properties.spring.json.trusted.packages=*

# Logging
logging.level.org.springframework.kafka=INFO
logging.level.org.apache.kafka=INFO

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REST API Endpoints

Method	Endpoint	Parameters	Description
GET	/api/message	None	Returns all messages consumed from Kafka.
POST	/api/message	Messages JSON object in request body	Sends a message to Kafka.

Example Request (POST)

POST http://localhost:8080/api/message
Content-Type: application/json

{
    "sender": "Tornov",
    "content": "Hello Kafka",
    "time": "2025-10-12T22:00:00"
}

Example Response (GET)

{

  "sender": "Tornov",
  "content": "Hello Kafka",
  "time": "2025-10-12T22:00:00"

}

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Notes

• Kafka runs on port 9092.
• Spring Boot backend runs on port 8080.
• Messages are sent as plain strings to the Kafka topic chat_topic.
• No frontend included , fully backend and REST API driven.