Event streaming concept in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka producer code snippet?

Consider this Kafka producer code in Java that sends a message to a topic named test-topic. What will be printed on the console?

Kafka

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");
props.put("value.serializer", "org.apache.kafka.common.serialization.StringSerializer");

Producer<String, String> producer = new KafkaProducer<>(props);
ProducerRecord<String, String> record = new ProducerRecord<>("test-topic", "key1", "Hello Kafka");
producer.send(record, (metadata, exception) -> {
    if (exception == null) {
        System.out.println("Sent to partition " + metadata.partition());
    } else {
        System.out.println("Error sending message");
    }
});
producer.close();

A Sent to partition 0

B Error sending message

C Sent to partition 1

D No output

💡 Hint

Assume the topic test-topic has only one partition.

The message is sent successfully to the only partition (partition 0) of the topic, so the callback prints "Sent to partition 0".

🧠 Conceptual

intermediate

What does Kafka's consumer group ensure?

In Kafka, what is the main purpose of a consumer group?

A To allow multiple consumers to read the same message independently

B To distribute partitions among consumers for parallel processing

C To store messages permanently in Kafka topics

D To encrypt messages during transmission

💡 Hint

Think about how Kafka balances workload among consumers.

A consumer group allows Kafka to assign partitions to consumers so they can process messages in parallel without duplication.

🔧 Debug

advanced

Why does this Kafka consumer code fail to receive messages?

Look at this Kafka consumer code snippet. It never prints any consumed messages. What is the cause?

Kafka

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "group1");
props.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
props.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");

KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props);
consumer.subscribe(Collections.singletonList("my-topic"));

while (true) {
    ConsumerRecords<String, String> records = consumer.poll(Duration.ofMillis(100));
    for (ConsumerRecord<String, String> record : records) {
        System.out.println("Received: " + record.value());
    }
}

A The consumer does not call consumer.close(), causing resource leak

B The consumer group ID is missing, causing subscription failure

C The consumer never commits offsets, so it reads no messages

D The consumer does not call poll() correctly to fetch messages

💡 Hint

Check the poll method usage and its parameters.

The poll method requires a timeout duration. If the argument is incorrect or missing, the consumer will not fetch messages.

📝 Syntax

advanced

Which Kafka Streams code snippet compiles without error?

Which of these Kafka Streams Java code snippets correctly creates a stream from topic input-topic?

A

StreamsBuilder builder = new StreamsBuilder();
KStream<String, String> stream = builder.stream("input-topic");

B

StreamsBuilder builder = new StreamsBuilder()
KStream<String, String> stream = builder.stream("input-topic")

C

StreamsBuilder builder = new StreamsBuilder();
KStream<String, String> stream = builder.stream(input-topic);

D

StreamsBuilder builder = new StreamsBuilder();
KStream<String, String> stream = builder.stream('input-topic');

💡 Hint

Check for correct Java syntax and string literals.

Option A uses correct Java syntax with semicolons and double quotes for string literals. Others have syntax errors.

🚀 Application

expert

How many partitions will be assigned to each consumer in this group?

A Kafka topic has 6 partitions. There are 3 consumers in the same consumer group subscribed to this topic. How many partitions will each consumer get assigned?

A Each consumer gets 3 partitions

B Each consumer gets 1 partition

C Each consumer gets 2 partitions

D All consumers get all 6 partitions

💡 Hint

Partitions are divided evenly among consumers in a group.

Kafka assigns partitions evenly among consumers in a group. 6 partitions divided by 3 consumers means each gets 2 partitions.