ConsumerDemo.java

package kafka.tutorial1;


import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.ConsumerRecord;
import org.apache.kafka.clients.consumer.ConsumerRecords;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.serialization.StringDeserializer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.time.Duration;
import java.util.Arrays;
import java.util.Properties;

public class ConsumerDemo {
    public static void main(String[] args) {

        Logger logger = LoggerFactory.getLogger(ConsumerDemo.class.getName());

        String bootstrapServers = "127.0.0.1:9092";
        String groupId = "my-fourth-application";
        String topic = "first_topic";

        //create consumer properties or configs
        Properties properties = new Properties();
        properties.setProperty(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrapServers);
        properties.setProperty(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.setProperty(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        properties.setProperty(ConsumerConfig.GROUP_ID_CONFIG, groupId);
        properties.setProperty(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");

        //create consumer
        KafkaConsumer<String, String> consumer =
                new KafkaConsumer<String, String>(properties);

        //subscribe consumer to our topic(s)
        consumer.subscribe(Arrays.asList(topic));

        //poll for new data
        while (true) {
            ConsumerRecords<String, String> records =
                    consumer.poll(Duration.ofMillis(100));

            for (ConsumerRecord record : records){
                logger.info("Key: " + record.key() + ", Value: " + record.value());
                logger.info("Partition: " + record.partition() + ", Offset: " + record.offset());
            }
        }

    }
}