Image source from Cloudkarafka

In this tutorial/lab, you will experience a very simple and quick hands-on experience with:

Java
Springboot
Apache Kafka
Zookeeper

Requirements

Homebrew
Testing with Postman. To learn more, you can watch this video.
Understanding the core concept of Kafka

Installment

Install Java 8

$ brew tap adoptopenjdk/openjdk
$ brew cask install adoptopenjdk8

Install Kafka

$ brew install kafka

Open the 1st terminal to start Zookeeper

$ zookeeper-server-start /usr/local/etc/kafka/zookeeper.properties

Open the 2nd terminal to start Kafka

$ kafka-server-start /usr/local/etc/kafka/server.properties

Open the 3rd terminal to create a Kafka topic

$ kafka-topics --bootstrap-server localhost:9092 --topic <enter-a-topic> --create --partitions 1 --replication-factor 1

Create a Maven project with Springboot

Open start.spring.io
Choose Spring Web & Spring for Apache Kafka dependencies
Open your project in IDE (I prefer to use IntelliJ)

Configure Kafka Producer and Consumer

Add this to application.properties in src/main/resources folder, and modify the highlights:

spring.datasource.url=jdbc:mysql://localhost:3306/<your-db-name>?allowPublicKeyRetrieval=true&useSSL=false&serverTimezone=UTC
spring.datasource.username=<your-db-username>
spring.datasource.password=<your-db-password>

app.topic=<same-topic-created-in-terminal>

spring.kafka.bootstrap-servers=localhost:9092
spring.kafka.groupId=<any-group-id>

spring.kafka.consumer.bootstrap-servers=localhost:9092
spring.kafka.consumer.group-id=<any-group-id>
spring.kafka.consumer.auto-offset-reset=earliest
spring.kafka.consumer.key-deserializer=org.apache.kafka.common.serialization.StringDeserializer
spring.kafka.consumer.value-deserializer=org.apache.kafka.common.serialization.StringDeserializer

spring.kafka.producer.bootstrap-servers=localhost:9092
spring.kafka.producer.value-serializer=org.apache.kafka.common.serialization.StringSerializer
spring.kafka.producer.key-serializer=org.apache.kafka.common.serialization.StringSerializer

Open a new terminal, and create a topic:

kafka-topics --bootstrap-server localhost:9092 --topic <same-topic-in-application.properties> --create --partitions 1 --replication-factor 1

Initialize Kafka Producer & Receiver Service

Inside the package com.example, create these folders: $ mkdir controller model repository service
Create Producer and Receiver Services: $ touch service/KafkaConsumer.java service/KafkaProducer.java
Add this to KafkaConsumer:

package <enter-your-package-here>;

import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Service;
import java.util.ArrayList;
import java.util.List;
@Service
public class KafkaConsumer {
    public static List<String> messages = new ArrayList<>();
    private final static String topic = "<same-topic-in-resources>";
    private final static String groupId = "<same-group-id>";

    @KafkaListener(topics = topic, groupId = groupId)
    public void listen(String message) {
        messages.add(message);
    }
}

Add this code to KafkaProducer:

package <enter-your-package-here>;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.kafka.core.KafkaTemplate;
import org.springframework.stereotype.Service;

@Service
public class KafkaProducer {

    @Autowired
    private KafkaTemplate<String, String> kafkaTemplate;

    @Value("${app.topic}")
    private String topic;

    public void produce(String message) {
        kafkaTemplate.send(topic, message);
    }
}

Create Kafka API

Create a Kafka controller file: $ touch controller/kafkaController.java and add this:

package server.controller;

import org.springframework.web.bind.annotation.*;

import server.service.KafkaConsumer;
import server.service.KafkaProducer;

import org.springframework.beans.factory.annotation.Autowired;

import java.util.List;

@RestController
public class KafkaController {
  @Autowired
  private KafkaConsumer consumer;

  @Autowired
  private KafkaProducer producer;

  @PostMapping("/send")
  public void send(@RequestBody String data) {
    producer.produce(data);
  }
  @GetMapping("/receive")
  public List<String> receive() {
    return consumer.messages;
  }

  public KafkaConsumer getConsumer() {
    return consumer;
  }

  public KafkaProducer getProducer() {
    return producer;
  }

  public void setConsumer(KafkaConsumer consumer) {
    this.consumer = consumer;
  }

  public void setProducer(KafkaProducer producer) {
    this.producer = producer;
  }
}

NOTE: There are also models and repository, which you use to configure with your database, but we don’t need it in this tutorial.

Final Project Structure

Testing

There are 2 ways to send the message from the producer: Postman & Terminal.

Open the 3rd terminal that you used to create the topic earlier

$ kafka-console-consumer --bootstrap-server localhost:9092 --topic <enter-your-topic> --from-beginning

1. Postman

Use POST/ method and enter localhost:8080/send with the JSON body:

{
   "message": "Hello from Postman"
}

2. Terminal
Open the 4th terminal, and type:

$ kafka-console-producer --broker-list localhost:9092 --topic <enter-your-topic>
> Hello from the terminal

Check the terminal, you will see the message that you sent via postman and terminal in real-time.

Done & Congratulations!

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