Java, How to get number of messages in a topic in apache kafka

Question

I am using apache kafka for messaging. I have implemented the producer and consumer in Java. How can we get the number of messages in a topic?

Answer 1

Using the Java client of Kafka 2.11-1.0.0, you can do the following thing :

    KafkaConsumer consumer = new KafkaConsumer<>(props);
    consumer.subscribe(Collections.singletonList("test"));
    while(true) {
        ConsumerRecords records = consumer.poll(100);
        for (ConsumerRecord record : records) {
            System.out.printf("offset = %d, key = %s, value = %s%n", record.offset(), record.key(), record.value());

            // after each message, query the number of messages of the topic
            Set partitions = consumer.assignment();
            Map offsets = consumer.endOffsets(partitions);
            for(TopicPartition partition : offsets.keySet()) {
                System.out.printf("partition %s is at %d\n", partition.topic(), offsets.get(partition));
            }
        }
    }

Output is something like this :

offset = 10, key = null, value = un
partition test is at 13
offset = 11, key = null, value = deux
partition test is at 13
offset = 12, key = null, value = trois
partition test is at 13