Java producer client in Kafka - Step-by-Step Execution

Process Flow - Java producer client

Create Properties

↓

Create KafkaProducer

↓

Create ProducerRecord

↓

Send Record asynchronously

↓

Callback on completion

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Close Producer

This flow shows how a Java Kafka producer client is created, sends a message asynchronously, handles the callback, and then closes.

Execution Sample

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<>("my-topic", "key1", "value1");
producer.send(record, (metadata, exception) -> {
  if (exception == null) System.out.println("Sent");
});
producer.close();

This code creates a Kafka producer, sends a message with key and value to a topic, prints confirmation on success, and closes the producer.

Process Table

Step	Action	State Change	Output
1	Create Properties object	Properties with bootstrap.servers=localhost:9092 and serializers
2	Create KafkaProducer with properties	KafkaProducer ready to send messages
3	Create ProducerRecord with topic=my-topic, key=key1, value=value1	ProducerRecord ready
4	Call producer.send(record, callback)	Send request queued asynchronously
5	Callback triggered after send	No state change	Prints: Sent
6	Call producer.close()	Producer closed, resources freed

💡 Producer closed, no more messages can be sent

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 6
props	empty	contains bootstrap.servers and serializers	unchanged	unchanged	unchanged	unchanged
producer	null	null	KafkaProducer instance	KafkaProducer instance	KafkaProducer instance	closed
record	null	null	null	ProducerRecord instance	ProducerRecord instance	ProducerRecord instance

Key Moments - 3 Insights

Why does the send method not block the program until the message is sent?

Because send is asynchronous and queues the message to be sent in the background, as shown in step 4 of the execution_table.

What happens if we try to send a message after calling producer.close()?

The producer is closed and cannot send messages anymore, so sending after close will cause an error or no action, as noted in the exit_note.

Why do we provide a callback to the send method?

The callback runs when the send completes, letting us know if it succeeded or failed, as shown in step 5 where it prints 'Sent' on success.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state of the producer variable after step 2?

A closed

B null

C KafkaProducer instance ready to send messages

D ProducerRecord instance

💡 Hint

Check the variable_tracker row for 'producer' after Step 2

At which step does the callback print 'Sent'?

A Step 3

B Step 5

C Step 4

D Step 6

💡 Hint

Look at the output column in the execution_table for the callback action

If we remove the callback from send, what changes in the execution_table?

A Step 5 output would be empty, no confirmation printed

B Producer would not send messages

C Producer would close immediately

D Properties would be empty

💡 Hint

Step 5 shows the callback printing 'Sent'; without callback, no output occurs there

Concept Snapshot

Java Kafka Producer Client:
- Create Properties with bootstrap.servers and serializers
- Instantiate KafkaProducer with Properties
- Create ProducerRecord with topic, key, value
- Send record asynchronously with send(record, callback)
- Callback confirms success or failure
- Close producer to free resources

Full Transcript

This visual execution shows how a Java Kafka producer client works step-by-step. First, we create a Properties object and set the bootstrap server address and serializers. Then, we create a KafkaProducer instance using these properties. Next, we prepare a ProducerRecord with the topic name, key, and value. We send this record asynchronously using the send method, providing a callback that runs when the send completes. The callback prints 'Sent' if the message was sent successfully. Finally, we close the producer to release resources. Variables like props, producer, and record change state as the program runs. The send method does not block; it queues the message to send in the background. The callback lets us know when sending finishes. After closing the producer, no more messages can be sent.