java_kafkasamples/src/main/java/KafkaConsumerApp.java

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.TopicPartition;
import org.apache.kafka.common.serialization.StringDeserializer;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Properties;

public class KafkaConsumerApp {

    public static final String STRING_DESERIALIZER = StringDeserializer.class.getName();
    public static final String TOPIC = "my-topic";
    public static final Integer TIMEOUT = 200;

    public static void main(String[] args) {
        Properties props = new Properties();
        // We use "put" since there are strings. Otherwise, use setProperty.
        // These are the 3 required properties.
        // 1. Cluster membership: partition leaders, etc
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092, BROKER-1:9092, BROKER-2:9093");

        // 2. How keys and values are deserialized.
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());

        // 3. The consumer Group ID is now required.
        props.put(ConsumerConfig.GROUP_ID_CONFIG, "demo");

        KafkaConsumer<String, String> myConsumer = new KafkaConsumer<String, String>(props);
        myConsumer.subscribe(Arrays.asList(TOPIC));

        Boolean started = false;
        Integer pass = 0;
        try {
            while (true) {
                ConsumerRecords<String, String> records = myConsumer.poll(TIMEOUT);
                if (!started) {
                    started = true;
                    System.out.printf("Started");
                }
//                for (ConsumerRecord<String, String> cr : records.records(TOPIC)) {
//                    System.out.printf("\t\tKey: %s Value: %s\n", cr.key(), cr.value());
//                }
                for (ConsumerRecord<String, String> cr : records) {
                    System.out.printf("Pass: %d/%d Topic: %s Partition: %d, Offset: %d, Key: %s Value: %s\n",
                            pass, records.count(),
                            cr.key(), cr.partition(), cr.offset(), cr.key(), cr.value());
                }
                pass++;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            myConsumer.close();
        }
    }

    private static void assignDemo(KafkaConsumer<String, String> c) {
        TopicPartition partition0 = new TopicPartition(TOPIC, 0);
        ArrayList<TopicPartition> partitions = new ArrayList<TopicPartition>();
        partitions.add(partition0);

        c.assign(partitions); // NOT incremental !
    }

    private static void subscribeExamples(KafkaConsumer<String, String> c) {
        // In tutorial but does not compile: needs a rebalance callback
        // c.subscribe("my-*");
        // Maybe that way ?
        // c.subscribe(Pattern.compile("my-[\\w]+"), null);

        // Typical initial subscription.
        c.subscribe(Arrays.asList(TOPIC));

        // Replaces the current subscription set, does not extend it
        c.subscribe(Arrays.asList("another-topic"));

        // Better for incremental cases.
        ArrayList<String> topics = new ArrayList<String>();
        topics.add(TOPIC);
        topics.add("my-other-topic");
        topics.add("yetAnotherTopic");
        c.subscribe(topics);

        // Unsubcribe all topics.
        c.unsubscribe();

        // Alternative
        topics.clear();
        c.subscribe(topics);
    }
}