Java producer client 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 Java Kafka producer code snippet. 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");

KafkaProducer<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 Sent to partition: 0

B Send failed

C Sent to partition: 1

D Compilation error

💡 Hint

By default, Kafka assigns messages to partition 0 if no custom partitioner is set and only one partition exists.

The code sends a message to the topic "test-topic". If the topic has only one partition (partition 0), the message will be sent there. The code prints the partition number, so the output is "Sent to partition: 0".

🧠 Conceptual

intermediate

Which property is required to specify the Kafka broker address in a Java producer client?

When configuring a Kafka producer in Java, which property key must be set to specify the Kafka broker address?

A bootstrap.servers

B broker.address

C kafka.broker

D server.address

💡 Hint

It usually contains the word 'bootstrap'.

The correct property to specify Kafka broker addresses is bootstrap.servers. It tells the producer where to connect initially.

🔧 Debug

advanced

What error does this Kafka producer code raise?

Examine the following Java 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

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

A NullPointerException

B ClassNotFoundException for StringSerializer

C No error, message sent successfully

D org.apache.kafka.common.KafkaException: Missing value serializer

💡 Hint

Check if all required serializer properties are set.

The producer requires both key.serializer and value.serializer properties. Missing value.serializer causes a KafkaException indicating the serializer is missing.

📝 Syntax

advanced

Which option fixes the syntax error in this Kafka producer code?

Identify the option that fixes the syntax error in the following Java Kafka producer snippet:

KafkaProducer producer = new KafkaProducer(props);
ProducerRecord record = new ProducerRecord<>("topic", "key", "value")
producer.send(record);
producer.close();

A Remove diamond operator and add semicolon after ProducerRecord line

B Add diamond operator in constructor and semicolon after ProducerRecord line

C Add semicolon after producer.send(record) line only

D No changes needed, code is correct

💡 Hint

Check missing semicolons and proper generic usage.

The ProducerRecord line is missing a semicolon. Also, the KafkaProducer constructor should use diamond operator <> for type safety. Option B fixes both issues.

🚀 Application

expert

How many messages are sent by this Kafka producer code?

Given the following Java 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");

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

A 0

B 5

C 3

D 2

💡 Hint

Look at the loop and the break statement carefully.

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