Producer API basics in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka Producer code snippet?

Consider the following Kafka Producer code in Java. What will be printed to 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", "value1");

try {
    RecordMetadata metadata = producer.send(record).get();
    System.out.println("Sent to partition: " + metadata.partition());
} catch (Exception e) {
    System.out.println("Send failed");
}
producer.close();

A Send failed

B Sent to partition: 0

C Sent to partition: 1

D Compilation error

💡 Hint

By default, Kafka assigns messages to partition 0 if no custom partitioner is set and the topic has one partition.

The code sends a message to the topic "test-topic" which by default has one partition (partition 0). The send is synchronous using get(), so the metadata returned shows partition 0.

🧠 Conceptual

intermediate

Which property controls the Kafka Producer's acknowledgment behavior?

In Kafka Producer configuration, which property determines how many acknowledgments the producer requires the leader to receive before considering a request complete?

A acks

B batch.size

C retries

D linger.ms

💡 Hint

Think about the property that controls message durability guarantees.

The acks property controls the number of acknowledgments the leader broker must receive before the producer considers the send successful. Other options control retries, batch size, and delay.

🔧 Debug

advanced

What error does this Kafka Producer code raise?

Examine the following Kafka Producer code snippet. What error will it raise when run?

Kafka

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

Producer<String, String> producer = new KafkaProducer<>(props);

ProducerRecord<String, String> record = new ProducerRecord<>("test-topic", "key1", "value1");
producer.send(record);
producer.close();

A ClassNotFoundException for StringSerializer

B NullPointerException at send()

C No error, message sent successfully

D org.apache.kafka.common.KafkaException: Failed to construct kafka producer

💡 Hint

Check if all required serializer properties are set.

The value.serializer property is missing, so Kafka cannot create the producer properly and throws a KafkaException during construction.

📝 Syntax

advanced

Which option correctly creates a Kafka Producer with String key and value?

Choose the correct Java code snippet that creates a Kafka Producer with String key and value serializers.

A

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("key.serializer", new StringSerializer());
props.put("value.serializer", new StringSerializer());
Producer<String, String> producer = new KafkaProducer<>(props);

B

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("key.serializer", StringSerializer.class.getName());
props.put("value.serializer", StringSerializer.class.getName());
Producer<String, String> producer = new KafkaProducer<>(props);

C

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);

D

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("key.serializer", "StringSerializer");
props.put("value.serializer", "StringSerializer");
Producer<String, String> producer = new KafkaProducer<>(props);

💡 Hint

The serializer properties require the full class name as a string.

The correct way is to provide the full class name as a string. Options B and C use wrong types, and D uses incomplete class names causing errors.

🚀 Application

expert

How many messages are sent in this Kafka Producer loop?

Given the following Kafka Producer code, how many messages will be sent to the topic?

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);

for (int i = 0; i < 5; i++) {
    ProducerRecord<String, String> record = new ProducerRecord<>("test-topic", "key" + i, "value" + i);
    producer.send(record);
    if (i == 2) {
        break;
    }
}
producer.close();

A 3

B 5

C 2

D 0

💡 Hint

Consider the effect of the break statement inside the loop.

The loop runs from i=0 to i=4 but breaks when i==2, so it sends messages for i=0,1,2 only, totaling 3 messages.