Java Kafka Producer Example: Send Messages to a Topic

To send a message to Kafka in Java, you can use the 'KafkaProducer' class from the Kafka Clients library. Here is an example code snippet:

import org.apache.kafka.clients.producer.*;

import java.util.Properties;

public class KafkaProducerExample {

    public static void main(String[] args) {

        // set up the producer 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');

        // create a KafkaProducer instance
        Producer<String, String> producer = new KafkaProducer<>(props);

        // create a message to send
        String topic = 'my-topic';
        String key = 'my-key';
        String value = 'Hello, Kafka!';

        // create a ProducerRecord instance with the topic, key, and value
        ProducerRecord<String, String> record = new ProducerRecord<>(topic, key, value);

        // send the message
        producer.send(record);

        // close the producer
        producer.close();
    }
}

In this example, we first set up the producer properties, including the Kafka broker address, key and value serializers. Then, we create a 'KafkaProducer' instance with these properties. Next, we create a message to send, consisting of a topic, key, and value. We use these to create a 'ProducerRecord' instance. Finally, we call the 'send()' method on the producer instance to send the message, and close the producer.