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.

Practice

1. What is the main purpose of the Kafka Producer API?

easy

A. To send messages to Kafka topics

B. To read messages from Kafka topics

C. To manage Kafka cluster configurations

D. To monitor Kafka broker health

Solution

1. Step 1: Understand Kafka Producer role

   The Producer API is designed to send data to Kafka topics, acting as the message sender.

2. Step 2: Differentiate from other Kafka APIs

   Reading messages is done by the Consumer API, not the Producer API.

3. Final Answer:

   To send messages to Kafka topics -> Option A

4. Quick Check:

   Producer API = send messages [OK]

Hint: Producer API sends data; Consumer API reads data [OK]

Common Mistakes:

• Confusing Producer with Consumer API
• Thinking Producer manages cluster
• Assuming Producer monitors brokers

2. Which of the following is the correct way to create a Kafka Producer in Java?

easy

A. Producer<String> producer = new Producer(props);

B. KafkaProducer producer = new KafkaProducer<>(props);

C. KafkaProducer producer = new KafkaProducer();

D. KafkaProducer producer = KafkaProducer.create(props);

Solution

1. Step 1: Recall KafkaProducer constructor usage

   The KafkaProducer class requires properties and type parameters for key and value types.

2. Step 2: Check each option's syntax

   KafkaProducer producer = new KafkaProducer<>(props); correctly uses generics and constructor with properties. Others miss generics, constructor, or use invalid methods.

3. Final Answer:

   KafkaProducer producer = new KafkaProducer<>(props); -> Option B

4. Quick Check:

   Correct constructor with generics = KafkaProducer producer = new KafkaProducer<>(props); [OK]

Hint: Use new KafkaProducer<>(props) with key and value types [OK]

Common Mistakes:

• Omitting generics for key and value
• Using wrong constructor or method
• Not passing properties object

3. What will be the output of the following Java code snippet?

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 producer = new KafkaProducer<>(props);
ProducerRecord record = new ProducerRecord<>("my-topic", "key1", "value1");
producer.send(record);
System.out.println("Message sent");
producer.close();

medium

A. No output

B. Compilation error

C. Message sent

D. Runtime exception due to missing topic

Solution

1. Step 1: Analyze producer setup and send call

   The code sets up properties correctly, creates a producer, and sends a message to "my-topic" with key and value.

2. Step 2: Check output statement and close

   After sending, it prints "Message sent" and closes the producer. No errors expected if Kafka broker is running.

3. Final Answer:

   Message sent -> Option C

4. Quick Check:

   Successful send prints message [OK]

Hint: If send() succeeds, print statement runs [OK]

Common Mistakes:

• Assuming send() is synchronous and blocks
• Thinking missing topic causes error here
• Ignoring need for running Kafka broker

4. Identify the error in this Kafka Producer code snippet:

Properties props = new Properties();
props.put("bootstrap.servers", "localhost:9092");
props.put("key.serializer", "StringSerializer");
props.put("value.serializer", "StringSerializer");
KafkaProducer producer = new KafkaProducer<>(props);
ProducerRecord record = new ProducerRecord<>("topic", "key", "value");
producer.send(record);
producer.close();

medium

A. Missing topic name in ProducerRecord

B. Properties object not initialized

C. Producer not closed properly

D. Incorrect serializer class names

Solution

1. Step 1: Check serializer class names in properties

   The serializer values must be full class names like "org.apache.kafka.common.serialization.StringSerializer".

2. Step 2: Verify other code parts

   Topic name is present, producer is closed properly, and properties object is initialized correctly.

3. Final Answer:

   Incorrect serializer class names -> Option D

4. Quick Check:

   Serializer class names must be full package names [OK]

Hint: Use full serializer class names with package [OK]

Common Mistakes:

• Using short class names without package
• Forgetting to close producer
• Leaving topic name empty

5. You want to send messages with keys to ensure ordering per key in Kafka. Which ProducerRecord constructor should you use?

hard

A. ProducerRecord(String topic, K key, V value)

B. ProducerRecord(String topic, V value)

C. ProducerRecord(K key, V value)

D. ProducerRecord(String topic)

Solution

1. Step 1: Understand ordering by key in Kafka

   Kafka guarantees ordering within a partition, and keys determine partition assignment.

2. Step 2: Identify correct ProducerRecord constructor

   To send with a key, use the constructor that includes topic, key, and value.

3. Final Answer:

   ProducerRecord(String topic, K key, V value) -> Option A

4. Quick Check:

   Use constructor with topic, key, and value for ordering [OK]

Hint: Include key in ProducerRecord to maintain order [OK]

Common Mistakes:

• Using constructor without key loses ordering
• Omitting topic causes errors
• Confusing key and value parameters