Apache Kafka get list of consumers on a specific topic

Ares91 :

As it can be guest from the title, is there a way to get the consumer list on a specific topic in java? Untill now Im able to get the list of topics like this

    final ListTopicsResult listTopicsResult = adminClient.listTopics();
    KafkaFuture<Set<String>> kafkaFuture = listTopicsResult.names();
    Set<String> map = kafkaFuture.get();

but I havent found a way to get the list of consumers on each topic

Katya Gorshkova :

I was recently solving the same problem for my kafka client tool. It is not easy, but the only way, which I found from the code is the following:

Properties props = ...//here you put your properties
AdminClient kafkaClient = AdminClient.create(props);

//Here you get all the consumer groups
List<String> groupIds = kafkaClient.listConsumerGroups().all().get().
                       stream().map(s -> s.groupId()).collect(Collectors.toList()); 

//Here you get all the descriptions for the groups
Map<String, ConsumerGroupDescription> groups = kafkaClient.
                                               describeConsumerGroups(groupIds).all().get();
for (final String groupId : groupIds) {
    ConsumerGroupDescription descr = groups.get(groupId);
    //find if any description is connected to the topic with topicName
    Optional<TopicPartition> tp = descr.members().stream().
                                  map(s -> s.assignment().topicPartitions()).
                                  flatMap(coll -> coll.stream()).
                                  filter(s -> s.topic().equals(topicName)).findAny();
            if (tp.isPresent()) {
                //you found the consumer, so collect the group id somewhere
            }
} 

This API is available from the version 2.0. There is probably a better way but I was not able to find one. You can also find the code on my bitbucket