Java producer client in Kafka - Mini Project: Build & Apply

Java Producer Client

📖 Scenario: You are building a simple Java program that sends messages to a Kafka topic. Kafka is like a post office where your program can send letters (messages) to a specific mailbox (topic).In this project, you will create a Java Kafka producer client that sends messages to a topic named test-topic.

🎯 Goal: Build a Java Kafka producer client that sends three messages to the test-topic Kafka topic.

📋 What You'll Learn

Create a Java Properties object with Kafka producer configuration

Create a Kafka Producer<String, String> object

Send three messages with keys and values to the test-topic

Close the producer after sending messages

💡 Why This Matters

🌍 Real World

Kafka producers are used in real applications to send data streams like logs, user activity, or sensor data to Kafka topics for processing.

💼 Career

Understanding how to build Kafka producer clients in Java is essential for backend developers working with real-time data pipelines and event-driven architectures.

1

Create Kafka producer configuration

Create a Properties object called props and set these exact properties:
bootstrap.servers to "localhost:9092",
key.serializer to "org.apache.kafka.common.serialization.StringSerializer",
and value.serializer to "org.apache.kafka.common.serialization.StringSerializer".

Kafka

import java.util.Properties;

// Your code here

Hint

Use props.put(key, value) to set each configuration property.

2

Create Kafka producer client

Create a Kafka Producer<String, String> object called producer using the props configuration.

Kafka

import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;

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");

// Your code here

Hint

Use new KafkaProducer<>(props) to create the producer.

3

Send messages to Kafka topic

Use the producer.send() method to send these three messages to the test-topic topic:
1. Key: "key1", Value: "Hello Kafka 1"
2. Key: "key2", Value: "Hello Kafka 2"
3. Key: "key3", Value: "Hello Kafka 3"
Use new ProducerRecord<>(topic, key, value) to create each message.

Kafka

import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;
import org.apache.kafka.clients.producer.ProducerRecord;
import java.util.Properties;

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 producer = new KafkaProducer(props);

// Your code here

Hint

Call producer.send() three times with the correct ProducerRecord arguments.

4

Close the Kafka producer and print confirmation

Close the producer using producer.close().
Then print exactly "Messages sent successfully" using System.out.println().

Kafka

import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.Producer;
import org.apache.kafka.clients.producer.ProducerRecord;
import java.util.Properties;

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 producer = new KafkaProducer(props);

producer.send(new ProducerRecord("test-topic", "key1", "Hello Kafka 1"));
producer.send(new ProducerRecord("test-topic", "key2", "Hello Kafka 2"));
producer.send(new ProducerRecord("test-topic", "key3", "Hello Kafka 3"));

// Your code here

Hint

Call producer.close() to release resources.
Use System.out.println("Messages sent successfully") to print the confirmation.

Practice

1. What is the primary role of a Java producer client in Kafka?

easy

A. To send messages to Kafka topics

B. To consume messages from Kafka topics

C. To manage Kafka brokers

D. To monitor Kafka cluster health

Solution

1. Step 1: Understand Kafka client roles

   Kafka has producers that send messages and consumers that receive messages.

2. Step 2: Identify the producer's function

   A Java producer client specifically sends messages to Kafka topics.

3. Final Answer:

   To send messages to Kafka topics -> Option A

4. Quick Check:

   Producer = send messages [OK]

Hint: Producer sends, consumer receives messages [OK]

Common Mistakes:

• Confusing producer with consumer
• Thinking producer manages brokers
• Assuming producer monitors cluster

2. Which of the following is the correct way to set the serializer for the key in a Java Kafka producer?

easy

A. props.add("key.serializer", "StringSerializer");

B. props.set("key.serializer", "StringSerializer");

C. props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer");

D. props.put("key.serializer", String.class);

Solution

1. Step 1: Recall how to set properties in Kafka producer

   Kafka producer uses Properties object with put(key, value) method.

2. Step 2: Identify correct serializer setting syntax

   The key.serializer must be set to the full class name as a string.

3. Final Answer:

   props.put("key.serializer", "org.apache.kafka.common.serialization.StringSerializer"); -> Option C

4. Quick Check:

   Use props.put with full serializer class name [OK]

Hint: Use props.put with full serializer class name string [OK]

Common Mistakes:

• Using props.set or props.add instead of put
• Not using full class name string
• Passing class type instead of string

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

import java.util.Properties;
import org.apache.kafka.clients.producer.*;
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<>("my-topic", "key1", "value1");
producer.send(record);
producer.close();
System.out.println("Message sent");

medium

A. Message sent

B. Compilation error due to missing imports

C. Runtime error due to missing Kafka server

D. No output

Solution

1. Step 1: Analyze the code flow

   The code creates a producer, sends a message, closes the producer, then prints "Message sent".

2. Step 2: Consider output behavior

   Assuming Kafka server is running and imports are correct, the print statement executes after send and close.

3. Final Answer:

   Message sent -> Option A

4. Quick Check:

   Print after send and close = "Message sent" [OK]

Hint: Print statement runs after send, shows "Message sent" [OK]

Common Mistakes:

• Assuming send() blocks until message delivered
• Ignoring that print runs regardless of Kafka server
• Confusing compile errors with runtime issues

4. Identify the error in this Java Kafka producer code snippet:

import java.util.Properties;
import org.apache.kafka.clients.producer.*;
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<>("my-topic");
producer.send(record);
producer.close();

medium

A. Producer not closed properly

B. Incorrect serializer class name

C. Missing bootstrap.servers property

D. ProducerRecord missing key argument

Solution

1. Step 1: Check ProducerRecord constructor usage

   The constructor used has only topic, but the generic type expects key and value.

2. Step 2: Identify mismatch in arguments

   ProducerRecord<String, String> expects key and value, but no key/value is provided, causing a compile error.

3. Final Answer:

   ProducerRecord missing key argument -> Option D

4. Quick Check:

   ProducerRecord requires key and value [OK]

Hint: ProducerRecord needs key and value if generics specify both [OK]

Common Mistakes:

• Using wrong ProducerRecord constructor
• Ignoring generic type mismatch
• Assuming value-only constructor works with key type

5. You want to send multiple messages to different Kafka topics using a single Java producer instance efficiently. Which approach is best?

hard

A. Create a new KafkaProducer for each message

B. Reuse one KafkaProducer and send ProducerRecords with different topics

C. Use multiple threads each with its own KafkaProducer

D. Send all messages to one topic and then move them to others

Solution

1. Step 1: Understand KafkaProducer resource usage

   Creating a producer is expensive; reusing one instance is efficient.

2. Step 2: Sending to multiple topics

   ProducerRecords can specify different topics; one producer can send to many topics.

3. Step 3: Evaluate other options

   Creating many producers wastes resources; sending all to one topic is incorrect.

4. Final Answer:

   Reuse one KafkaProducer and send ProducerRecords with different topics -> Option B

5. Quick Check:

   One producer, multiple topics via records [OK]

Hint: Reuse one producer; specify topic per ProducerRecord [OK]

Common Mistakes:

• Creating many producers wastes resources
• Sending all messages to one topic incorrectly
• Assuming each thread needs its own producer