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Java Example to Use Kafka Streams for Real-time Data

Overview​

This guide explains how to implement a Java Kafka consumer to receive onchain data streams from Bitquery in real-time using the Apache Kafka library. The consumer is secured with SSL and SASL, subscribing to a Kafka topic and logging messages to the console.

You can find the complete code here.

Prerequisites​

Ensure that you have the following components in place before running the code:

  1. Kafka Cluster: Accessible Kafka brokers from Bitquery.
  2. Username and Password: For authentication with the Kafka brokers.
  3. Topic name(s) to subscribe to.
  4. Java: JDK 8 or higher.
  5. Apache Kafka Client: Kafka client library for Java.

Additional Files​

  • Create a new Java Project
  • Download all the certificates and store them in the src/main/resources/ folder:
    • keystore.jks: SSL keystore file
    • clienttruststore.jks: SSL truststore file

Ensure that the paths and passwords in the configuration match your actual certificate files and credentials.

Dependencies​

The script relies on the Apache Kafka client library. Make sure to include it in your project's dependencies. If you're using Maven, add the following to your pom.xml:

<dependency>
    <groupId>org.apache.kafka</groupId>
    <artifactId>kafka-clients</artifactId>
    <version>3.4.0</version> <!-- Use the latest version -->
</dependency>

Kafka Client Initialization​

The Kafka client is initialized using the KafkaConsumer class from the Apache Kafka library. The client is configured with SSL and SASL to authenticate communication with the Kafka brokers.

import org.apache.kafka.clients.CommonClientConfigs;
import org.apache.kafka.clients.consumer.ConsumerConfig;
import org.apache.kafka.clients.consumer.KafkaConsumer;
import org.apache.kafka.common.config.SaslConfigs;
import org.apache.kafka.common.serialization.ByteArrayDeserializer;

Properties props = new Properties();
props.put(ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
        "rpk0.bitquery.io:9093,rpk1.bitquery.io:9093,rpk2.bitquery.io:9093");
props.put(ConsumerConfig.GROUP_ID_CONFIG, "trontest1-group-1");
props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "latest");
props.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, "30000");
props.put(SaslConfigs.SASL_MECHANISM, "SCRAM-SHA-512");
props.put(CommonClientConfigs.SECURITY_PROTOCOL_CONFIG, "SASL_SSL");
props.put("ssl.endpoint.identification.algorithm", "");

props.put(SaslConfigs.SASL_JAAS_CONFIG,
        "org.apache.kafka.common.security.scram.ScramLoginModule required username=\"ssss\" password=\"ssss\";");

props.put("ssl.keystore.location", "src/main/resources/keystore.jks");
props.put("ssl.keystore.password", "123456");
props.put("ssl.key.password", "123456");
props.put("ssl.truststore.location", "src/main/resources/clienttruststore.jks");
props.put("ssl.truststore.password", "truststorepassword");
  • group.id: A unique identifier for the consumer group.
  • bootstrap.servers: List of Kafka broker addresses.
  • SSL configuration: Paths to the keystore and truststore files are provided for SSL authentication.
  • SASL configuration: Username and password are used for secure communication.

Kafka Consumer Setup​

The Kafka consumer is initialized to consume messages from a specified topic. In this case, the consumer listens to the tron.broadcasted.transactions topic.

String topic = "tron.broadcasted.transactions";
KafkaConsumer<byte[], byte[]> consumer = new KafkaConsumer<>(props, new ByteArrayDeserializer(),
        new ByteArrayDeserializer());
consumer.subscribe(Collections.singletonList(topic));

Message Processing​

The consumer polls for new messages and processes them in a loop. Each message is converted from bytes to a string and printed to the console.

while (true) {
    ConsumerRecords<byte[], byte[]> records = consumer.poll(Duration.ofMillis(100));
    for (ConsumerRecord<byte[], byte[]> record : records) {
        String value = new String(record.value());
        System.out.println(value);
    }
}

Graceful Shutdown​

A shutdown hook is added to ensure the consumer closes gracefully when the application is terminated.

Runtime.getRuntime().addShutdownHook(new Thread(consumer::wakeup));

try {
    // Main consumer loop
} catch (WakeupException e) {
    // Ignore for shutdown
} finally {
    consumer.close();
}

Execution Workflow​

The following sequence of operations occurs when the script runs:

  1. Kafka Client Initialization: The Kafka client is initialized with SSL and SASL configurations.
  2. Group ID Assignment: A unique group.id is used to ensure independent message processing.
  3. Kafka Consumer Connection: The consumer subscribes to a Kafka topic.
  4. Message Processing:
    • Polling: The consumer polls messages from Kafka.
    • Logging: The message content is logged to the console.
  5. Graceful Shutdown: A shutdown hook ensures the consumer closes cleanly upon termination.