This repository is to save a message producer and cosumer project and a payment project.

• Apache Kafka (Kafdrop)
• Docker (Docker-Compose)
• Zookeeper
• Postman
• SpringBoot
• Java
• WSL (Linux on Windows)

Also, if you don't have IntelliJ license, you can create and run SpringBoot projects using the 'Sping Initializr Java Support' and 'Spring Boot Tools' extension in VS Code. They were built by Microsoft.

The objective with this project is to show how we can produce and consume messages using Apache Kafka with Kafdrop interface.

We will follow this flow at below:

The first step is run the docker-compose where the Zookeeper, Kafka and Kafdrop are ran.

If you have WSL installed with docker and docker-compose dependencies installed, just run in the command line docker-compose up -d. The -d is used to say to Docker to run it in the background and keep the command line free.

You will see in the Docker Desktop something like this:

To see the Kafdrop interface, you can access it in your browser at localhost:19000

Next, to run the project you need to be in the producer directory and to click in the play button and in another vscode you need to be in the consumer directory and do the same. It will create a topic at Kafdrop named by 'str-topic' as we can see in the image above.

With all things running fine, we finally can send a request to the producer that will be serialized and saved at Apache Kafka topic.

The endpoint was wrote in the StringProducerResource.java. As we can see in the code below, the request is a POST and the enpoint is /producer.

@RestController
@RequestMapping(value = "/producer")
public class StringProducerResource {

    private final StringProducerService producerService;

    @PostMapping
    public ResponseEntity<?> sendMessage(@RequestBody String message) {
        producerService.sendMessage(message);
        return ResponseEntity.status(HttpStatus.CREATED).build();
    }
}

So, the complete URL will be: localhost:8000/producer because the producer are listen in the door 8000 and it will accept a raw JSON.

The Producer is waiting a key named message and a value (string). The raw JSON must be like:

If the request was returned as 'CREATED' the request was OK.

To see the message consumed by the consumer, you can open the Kafdrop, click in the str-topic, see messages, and you will see the messages in the topics:

As the message in Kafdrop was saved, the consumer can take the massage from there if it knows which topic, partition and offset the message is in. As we created just 2 partitions in KafkaAdminConfig.java (.partitions(2)) as we can see in the code below, the message can be save in the partition 0 or 1, depending on the Kafka system or if you set it.

    @Bean
    public KafkaAdmin.NewTopics topics() {
        return new KafkaAdmin.NewTopics(
                TopicBuilder.name("str-topic").partitions(2).replicas(1).build()
        );
    }

To see the message being consumed by the Consumer, we can send another message:

{
    "message":"Apache Kafka repository"
}

Taking a look on the terminal where the Consumer is running, we can see the message be consumed

This project is very similar with the Producer and Consumer project. The difference is in the JSON message. Here, I prepared the software to receive a complete JSON object.

The main objective is to manage more than one informations received by requests and to create a Collection on Postman.

The body to be sent in the request needs to have the fields:

• id
• idUser
• idProduct
• cardNumber

Now, the request must be like this:

{
    "id":111,
    "idUser":22222,
    "idProduct":3,
    "cardNumber":"4444 5555 6666 7777 8888"
}

The request must use another endpoint: /payments

So, the complete URL will be: localhost:19000/payments

If the payment was sent (request), the consumer from the payment-service software should confirm if the data (JSON Body) is correct and validate the payment.

Now, we can see the requests done in the payment-topic on Kafdrop in the localhost:19000. The last one was saved on the Partition 0 and offset 2