Kafka integration basics in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when a Spring Boot Kafka listener receives a message?

Consider a Spring Boot Kafka listener configured to listen to topic "orders". When a message "Order123" is sent to this topic, what will the listener method print?

Spring Boot

import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;

@Component
public class OrderListener {

    @KafkaListener(topics = "orders")
    public void listen(String message) {
        System.out.println("Received: " + message);
    }
}

A Received: Order123

B No output, listener not triggered

C Received: null

D Order123

💡 Hint

The listener method prints a prefix before the message content.

The listener method prints "Received: " followed by the message content it receives from the Kafka topic.

📝 Syntax

intermediate

Which Kafka producer configuration property sets the Kafka server address?

In Spring Boot Kafka producer configuration, which property key correctly sets the Kafka broker address to localhost:9092?

A spring.kafka.producer.broker-address=localhost:9092

B spring.kafka.bootstrap-servers=localhost:9092

C spring.kafka.producer.server=localhost:9092

D spring.kafka.producer.bootstrap-servers=localhost:9092

💡 Hint

The property includes 'producer' and 'bootstrap-servers'.

The correct property to set Kafka broker address for producer is 'spring.kafka.producer.bootstrap-servers'.

🔧 Debug

advanced

Why does this Kafka listener fail to receive messages?

Given the following listener code, why does it not receive messages from the topic payments?

Spring Boot

import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;

@Component
public class PaymentListener {

    @KafkaListener(topic = "payments")
    public void listen(String message) {
        System.out.println("Payment received: " + message);
    }
}

A The listener method must return a value.

B The annotation property should be 'topics' not 'topic'.

C The class must implement an interface to receive messages.

D The method parameter type should be ConsumerRecord, not String.

💡 Hint

Check the spelling of the annotation property for topic subscription.

The @KafkaListener annotation requires the property 'topics' (plural) to specify the topic list. Using 'topic' causes the listener not to subscribe.

❓ state_output

advanced

What is the value of the message count after processing 3 messages?

A Spring Boot Kafka listener increments a counter each time it receives a message. After receiving 3 messages, what is the value of the counter?

Spring Boot

import org.springframework.kafka.annotation.KafkaListener;
import org.springframework.stereotype.Component;

@Component
public class CountingListener {

    private int messageCount = 0;

    @KafkaListener(topics = "events")
    public void listen(String message) {
        messageCount++;
    }

    public int getMessageCount() {
        return messageCount;
    }
}

A 0

B 1

C 3

D Cannot determine without synchronization

💡 Hint

The counter increments once per message received.

Each message increments messageCount by 1. After 3 messages, messageCount is 3.

🧠 Conceptual

expert

Which option best describes the role of Kafka consumer groups in Spring Boot?

In Spring Boot Kafka integration, what is the main purpose of assigning consumers to the same consumer group?

A To allow multiple consumers to share the load by dividing topic partitions among them

B To ensure all consumers receive every message from the topic

C To enable consumers to produce messages to the same topic

D To prevent consumers from connecting to the Kafka broker simultaneously

💡 Hint

Think about how Kafka distributes messages to consumers in a group.

Consumers in the same group share partitions of a topic so messages are load balanced and processed once per group.