poll() and commitAsync() in Spring-Kafka

Question

I am trying to write a kafka consumer application in java on Springboot platform. Earlier, I have written code in plain java but now converting into spring-kafka as it can give some advantage over plain java. I do have few questions that I am trying to understand.

It seems that I don't have to explicitly poll() loop in spring-kafka and it would be handled automatically by @KafkaListener?

I have set enable.auto.commit='false', As I have to do some processing before committing offsets, how can I perform commitAsync() in Spring-Kafka?

ConsumerConfig.java :

@EnableKafka
@Configuration
public class KafkaConsumerConfig {

    @Value("${app.kafka_brokers}")
    private String KAFKA_BROKERS;

    @Value("${app.topic}")
    private String KAFKA_TOPIC;

    @Value("${app.group_id_config}")
    private String GROUP_ID_CONFIG;

    @Value("${app.schema_registry_url}")
    private String SCHEMA_REGISTRY_URL;

    @Value("${app.offset_reset}")
    private String OFFSET_RESET;

    @Value("${app.max_poll_records}")
    private String MAX_POLL_RECORDS;

    @Value("${app.security.protocol}")
    private String SSL_PROTOCOL;

    @Value("${app.ssl.truststore.password}")
    private String SSL_TRUSTSTORE_SECURE;

    @Value("${app.ssl.keystore.password}")
    private String SSL_KEYSTORE_SECURE;

    @Value("${app.ssl.key.password}")
    private String SSL_KEY_SECURE;

    @Value("${app.ssl.truststore.location}")
    private String SSL_TRUSTSTORE_LOCATION_FILE_NAME;

    @Value("${app.ssl.keystore.location}")
    private String SSL_KEYSTORE_LOCATION_FILE_NAME;

    @Bean
    public ConsumerFactory<String, String> consumerFactory(){

        Map<String, Object> props = new HashMap<>();
        props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,KAFKA_BROKERS);
        props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, OFFSET_RESET);
        props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, StringDeserializer.class.getName());
        props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, KafkaAvroDeserializer.class.getName());
        props.put(ConsumerConfig.GROUP_ID_CONFIG, GROUP_ID_CONFIG);
        props.put(KafkaAvroDeserializerConfig.SCHEMA_REGISTRY_URL_CONFIG, SCHEMA_REGISTRY_URL);
        props.put(ConsumerConfig.ENABLE_AUTO_COMMIT_CONFIG, "false");

        props.put(CommonClientConfigs.SECURITY_PROTOCOL_CONFIG, SSL_PROTOCOL);
        props.put(SslConfigs.SSL_TRUSTSTORE_LOCATION_CONFIG,SSL_TRUSTSTORE_LOCATION_FILE_NAME);
        props.put(SslConfigs.SSL_TRUSTSTORE_PASSWORD_CONFIG, SSL_TRUSTSTORE_SECURE);
        props.put(SslConfigs.SSL_KEYSTORE_LOCATION_CONFIG,SSL_KEYSTORE_LOCATION_FILE_NAME);
        props.put(SslConfigs.SSL_KEYSTORE_PASSWORD_CONFIG, SSL_KEYSTORE_SECURE);
        props.put(SslConfigs.SSL_KEY_PASSWORD_CONFIG, SSL_KEY_SECURE);

        return new DefaultKafkaConsumerFactory<>(props);

    }

    @Bean
    ConcurrentKafkaListenerContainerFactory<String, String> 
    kafkaListenerContainerFactory() {

      ConcurrentKafkaListenerContainerFactory<String, String> factory =
                            new ConcurrentKafkaListenerContainerFactory<>();
      factory.setConsumerFactory(consumerFactory());
      factory.setConcurrency(3);
      return factory;
  }

}

KafkaConsumer.java :

@Component
public class KafkaConsumer {
    
    @KafkaListener(topics = "topic", groupId = "group")
    public void run(ConsumerRecord<String, GenericRecord> record) {
        
        System.out.println(record);
        
    <-- how to asyncCommit()--> 
    }

}

George George · Accepted Answer · 2020-09-21T14:12:10

First of all, I suggest you use the properties and AutoConfiguration set by Spring kafka instead of creating your own as it follows the DRY Principle: Don't Repeat Yourself.

spring:
  kafka:
    bootstrap-servers: ${app.kafka_brokers}
    consumer:
      auto-offset-reset: ${app.offset_reset}
      enable-auto-commit: false   // <---- disable auto committing
    ssl:
      protocol: ${app.security.protocol}
      key-store-location: ${app.ssl.keystore.location}
      key-store-password:  ${app.ssl.keystore.password}
      trust-store-location: ${app.ssl.truststore.location}
      trust-store-password: ${app.ssl.truststore.password}
  // And other properties
    listener:
      ack-mode: manual // This is what you need

The AckMode docs: https://docs.spring.io/spring-kafka/api/org/springframework/kafka/listener/ContainerProperties.AckMode.html

Essentially, manual is an asynchronous acknowledgment, while manual_immediate is synchronous.

Then inside your @KafkaListener component you can inject org.springframework.kafka.support.Acknowledgment object acknowledge your message.

@Component
public class KafkaConsumer {
    
    @KafkaListener(topics = "topic", groupId = "group")
    public void run(ConsumerRecord<String, GenericRecord> record, Acknowledgment acknowledgment) {
        
        System.out.println(record);
        
        acknowledgment.acknowledge();
    }

}

Here's the documentation for what can be injected into a @KafkaListener method: https://docs.spring.io/spring-kafka/reference/html/#message-listeners

poll() and commitAsync() in Spring-Kafka

2 Answers