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Using SDK to Receive/Send Message (Recommended)

Last updated: 2022-05-26 12:02:23

    Overview

    This document describes how to access CKafka to send/receive messages with the SDK for Java in a VPC.

    If you need to use SDKs for other languages, see SDK Documentation.

    Prerequisites

    Directions

    Step 1. Prepare configurations

    1. Upload the downloaded demo to the Linux server under the same VPC, log in to the server, and enter the VPC directory under javakafkademo.
    2. Modify kafka.properties in the resources directory under the VPC project.
      ## Configure the accessed network by copying the information in the Network column in the Access Mode section on the instance details page in the console
      bootstrap.servers=xx.xx.xx.xx:xxxx
      ## Configure the topic by copying the information on the Topic Management page in the console
      topic=XXX
      ## Configure the consumer group as needed
      group.id=XXX
      Parameter Description
      bootstrap.servers Accessed network, which can be copied in the Network column in the Access Mode section on the instance details page in the console.
      topic Topic name, which can be copied from the Topic Management page in the console.
      group.id You can customize it. After the demo runs successfully, you can see the consumer group on the Consumer Group page.

    Step 2. Send a message

    1. Compile and run the message producing program CKafkaProducerDemo.java.
      public class CKafkaProducerDemo {

      public static void main(String args[])
      {
      // Load `kafka.properties`.
      Properties kafkaProperties = CKafkaConfigurer.getCKafkaProperties();

      Properties properties = new Properties();
      // Set the access point. Get the access point of the corresponding topic in the console.
      properties.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaProperties.getProperty("bootstrap.servers"));

      // Set the method for serializing Kafka messages. `StringSerializer` is used in this demo.
      properties.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG,
      "org.apache.kafka.common.serialization.StringSerializer");
      properties.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG,
      "org.apache.kafka.common.serialization.StringSerializer");
      // Set the maximum request wait time.
      properties.put(ProducerConfig.MAX_BLOCK_MS_CONFIG, 30 * 1000);
      // Set the number of retries for the client.
      properties.put(ProducerConfig.RETRIES_CONFIG, 5);
      // Set the internal retry interval for the client.
      properties.put(ProducerConfig.RECONNECT_BACKOFF_MS_CONFIG, 3000);
      // Construct a producer object.
      KafkaProducer<string, string=""> producer = new KafkaProducer<>(properties);

      // Construct a CKafka message.
      String topic = kafkaProperties.getProperty("topic"); // Topic of the message. Enter the topic you created in the console
      String value = "this is ckafka msg value"; // Message content

      try {
      // Batch getting future objects can speed up the process. Note that the batch size should not be too large.
      List<future<recordmetadata>> futureList = new ArrayList<>(128);
      for (int i = 0; i < 10; i++)
      {
      // Send the message and get a future object.
      ProducerRecord<string, string=""> kafkaMsg = new ProducerRecord<>(topic,
      value + ": " + i);
      Future<recordmetadata> metadataFuture = producer.send(kafkaMsg);
      futureList.add(metadataFuture);

      }
      producer.flush();
      for (Future<recordmetadata> future : futureList)
      {
      // Sync the future object obtained.
      RecordMetadata recordMetadata = future.get();
      System.out.println("produce send ok: " + recordMetadata.toString());
      }
      } catch (Exception e) {
      // If the sending still fails after client internal retries, the system needs to report and handle the error.
      System.out.println("error occurred");
      }
      }
      }
    2. View the execution result.
      Produce ok:ckafka-topic-demo-0@198
      Produce ok:ckafka-topic-demo-0@199
    3. On the Topic Management tab on the instance details page in the CKafka console, select the target topic, and click More > Message Query to view the message just sent.

    Step 3. Consume messages

    1. Compile and run the message subscribing program CKafkaConsumerDemo.java.
      public class CKafkaConsumerDemo {

      public static void main(String args[])
      {
      // Load `kafka.properties`.
      Properties kafkaProperties = CKafkaConfigurer.getCKafkaProperties();

      Properties props = new Properties();
      // Set the access point. Get the access point of the corresponding topic in the console.
      props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafkaProperties.getProperty("bootstrap.servers"));
      // Set the maximum interval between two polls.
      // If the consumer does not return a heartbeat message within the interval, the broker will determine that the consumer is not alive, and then remove the consumer from the consumer group and trigger rebalancing. The default value is 30s.
      props.put(ConsumerConfig.SESSION_TIMEOUT_MS_CONFIG, 30000);
      // Set the maximum number of messages that can be polled at a time.
      // Do not set this parameter to an excessively large value. If polled messages are not all consumed before the next poll starts, load balancing is triggered and lagging occurs.
      props.put(ConsumerConfig.MAX_POLL_RECORDS_CONFIG, 30);
      // Set the method for deserializing messages.
      props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG,
      "org.apache.kafka.common.serialization.StringDeserializer");
      props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG,
      "org.apache.kafka.common.serialization.StringDeserializer");
      // The instances in the same consumer group consume messages in load balancing mode.
      props.put(ConsumerConfig.GROUP_ID_CONFIG, kafkaProperties.getProperty("group.id"));
      // Construct a consumer object. This generates a consumer instance.
      KafkaConsumer<string, string=""> consumer = new KafkaConsumer<>(props);
      // Set one or more topics to which the consumer group subscribes.
      // We recommend you configure consumer instances with the same `GROUP_ID_CONFIG` value to subscribe to the same topics.
      List<string> subscribedTopics = new ArrayList<>();
      // If you want to subscribe to multiple topics, add the topics here.
      // You must create the topics in the console in advance.
      String topicStr = kafkaProperties.getProperty("topic");
      String[] topics = topicStr.split(",");
      for (String topic : topics)
      {
      subscribedTopics.add(topic.trim());
      }
      consumer.subscribe(subscribedTopics);

      // Consume messages in loop.
      while (true) {
      try {
      ConsumerRecords<string, string=""> records = consumer.poll(1000);
      // All messages must be consumed before the next poll, and the total duration cannot exceed the timeout interval specified by `SESSION_TIMEOUT_MS_CONFIG`.
      // We recommend you create an independent thread to consume messages and then return the result in async mode.
      for (ConsumerRecord<string, string=""> record : records) {
      System.out.println(
      String.format("Consume partition:%d offset:%d", record.partition(), record.offset()));
      }
      } catch (Exception e) {
      System.out.println("consumer error!");
      }
      }
      }
      }
    2. View the execution result.
      Consume partition:0 offset:298
      Consume partition:0 offset:299
    3. On the Consumer Group tab in the CKafka console, select the consumer group name, enter the topic name, and click View Details to view the consumption details.
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