Unable to get number of messages in kafka topic - apache-kafka

Question

I am fairly new to kafka. I have created a sample producer and consumer in java. Using the producer, I was able to send data to a kafka topic but I am not able to get the number of records in the topic using the following consumer code.
public class ConsumerTests {
public static void main(String[] args) throws Exception {
BasicConfigurator.configure();
String topicName = "MobileData";
String groupId = "TestGroup";
Properties properties = new Properties();
properties.put("bootstrap.servers", "localhost:9092");
properties.put("group.id", groupId);
properties.put("key.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
properties.put("value.deserializer", "org.apache.kafka.common.serialization.StringDeserializer");
KafkaConsumer<String, String> kafkaConsumer = new KafkaConsumer<>(properties);
kafkaConsumer.subscribe(Arrays.asList(topicName));
try {
while (true) {
ConsumerRecords<String, String> consumerRecords = consumer.poll(100);
System.out.println("Record count is " + records.count());
}
} catch (WakeupException e) {
// ignore for shutdown
} finally {
consumer.close();
}
}
}
I don't get any exception in the console but consumerRecords.count() always returns 0, even if there are messages in the topic. Please let me know, if I am missing something to get the record details.

Answer 1

The poll(...) call should normally be in a loop. It's always possible for the initial poll(...) to return no data (depending on the timeout) while the partition assignment is in progress. Here's an example:
try {
while (true) {
ConsumerRecords<String, String> records = consumer.poll(100);
System.out.println("Record count is " + records.count());
}
} catch (WakeupException e) {
// ignore for shutdown
} finally {
consumer.close();
}
For more info see this relevant article: