Consumer configuration in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka consumer configuration code?

Consider the following Kafka consumer configuration snippet in Java. What will be the value of props.getProperty("enable.auto.commit") after execution?

Kafka

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test-group");
props.put("enable.auto.commit", "false");
props.put("auto.commit.interval.ms", "1000");
String autoCommit = props.getProperty("enable.auto.commit");

A "true"

B "false"

C null

D Throws NullPointerException

💡 Hint

Check the value assigned to the key "enable.auto.commit" in the properties.

The property "enable.auto.commit" is explicitly set to "false" in the properties. So, calling getProperty returns "false".

❓ Predict Output

intermediate

What will be the output of this Kafka consumer poll timeout code?

Given the following Kafka consumer poll call, what is the type and meaning of the returned value?

Kafka

Consumer<String, String> consumer = new KafkaConsumer<>(props);
ConsumerRecords<String, String> records = consumer.poll(Duration.ofMillis(500));
System.out.println(records.count());

A Throws TimeoutException

B Always zero because poll timeout is too short

C Number of partitions assigned to the consumer

D Number of records fetched in 500 milliseconds

💡 Hint

The poll method returns records fetched within the timeout duration.

The poll method waits up to the specified timeout to fetch records. The count() method returns how many records were fetched.

❓ Predict Output

advanced

What error does this Kafka consumer configuration cause?

Analyze the following Kafka consumer configuration snippet. What error will occur when creating the consumer?

Kafka

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test-group");
props.put("enable.auto.commit", "maybe");
KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props);

A IllegalArgumentException due to invalid enable.auto.commit value

B TimeoutException on consumer creation

C NullPointerException because group.id is missing

D No error, consumer created successfully

💡 Hint

The enable.auto.commit property expects "true" or "false" only.

The property "enable.auto.commit" must be "true" or "false". Setting it to "maybe" causes an IllegalArgumentException.

🧠 Conceptual

advanced

How many partitions will the consumer subscribe to after this code?

Given a Kafka topic with 4 partitions, what is the number of partitions assigned to the consumer after this subscription code?

Kafka

consumer.subscribe(Collections.singletonList("my-topic"));
Set<TopicPartition> assigned = consumer.assignment();
int count = assigned.size();
System.out.println(count);

A 0

B 4

C 1

D Throws IllegalStateException

💡 Hint

Partitions are assigned only after poll() is called.

The assignment set is empty until consumer.poll() is called to trigger partition assignment.

❓ Predict Output

expert

What is the output of this Kafka consumer manual commit code?

Consider the following code snippet for manual offset commit. What will be printed?

Kafka

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("group.id", "test-group");
props.put("enable.auto.commit", "false");
props.put("auto.offset.reset", "earliest");
KafkaConsumer<String, String> consumer = new KafkaConsumer<>(props, new StringDeserializer(), new StringDeserializer());
consumer.subscribe(List.of("my-topic"));
ConsumerRecords<String, String> records = consumer.poll(Duration.ofMillis(1000));
for (ConsumerRecord<String, String> record : records) {
    System.out.println(record.offset() + ":" + record.value());
}
consumer.commitSync();
System.out.println("Committed offsets");

A Prints nothing and then 'Committed offsets'

B Prints records but never prints 'Committed offsets'

C Prints all records with offsets and values, then 'Committed offsets'

D Throws CommitFailedException

💡 Hint

Manual commit commits offsets after processing records.

The code polls records, prints each offset and value, then commits offsets synchronously and prints confirmation.