How to get All Topics in apache kafka?

Question

    @RequestMapping(value = "/getTopics",method = RequestMethod.GET)
    @ResponseBody
    public Response getAllTopics() {
        ZkClient zkClient = new ZkClient(ZookeeperProps.zookeeperURL, ZookeeperProps.connectionTimeoutMs,
                ZookeeperProps.sessionTimeoutMs, ZKStringSerializer$.MODULE$);
        Seq<String> topics = ZkUtils.getAllTopics(zkClient);
        scala.collection.Iterator<String> topicIterator = topics.iterator();
        String allTopics = "";
        while(topicIterator.hasNext()) {
            allTopics+=topicIterator.next();
            allTopics+="\n";
        }

        Response response = new Response();
        response.setResponseMessage(allTopics);
        return response;

    }

I am novice in apache kafka. Now a days trying to understand kafka with zookeeper. I want to fetch the topics associated with zookeeper. so I am trying following things
a:) first i made the zookeeper client as shown below :

ZkClient(ZookeeperProps.zookeeperURL, ZookeeperProps.connectionTimeoutMs, ZookeeperProps.sessionTimeoutMs, ZKStringSerializer$.MODULE$);
Seq<String> topics = ZkUtils.getAllTopics(zkClient);

but topics is blank set while executing with Java code.I am not getting what is problem here. My Zookeeper Props is as follow : String zkConnect = "127.0.0.1:2181"; And zookeeper is running perfectly fine.
Please help guys.

Mercurate

Answer 1

It's pretty simple. (My example is written in Java, but it would be almost the same in Scala.)

import java.util.List;

import org.apache.zookeeper.ZooKeeper;

public class KafkaTopicListFetcher {

    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper("localhost:2181", 10000, null);
        List<String> topics = zk.getChildren("/brokers/topics", false);
        for (String topic : topics) {
            System.out.println(topic);
        }
    }
}

The result when I have three topics: test, test2, and test 3

test
test2
test3

The picture below is what I drew for my own blog posting. It would be helpful when you understand the structure of ZooKeeper tree that Kafka uses. (It looks pretty small here. Open the image in a new tab and zoom in please.)

Johnathanjohnathon

With kafka 0.7x null is not acceptable value for watcher parameter in new ZooKeeper(...), need to have dummy parameter. – Sluiter

Answer 2

You can use kafka AdminClient . Below code snippet may help you:

Properties properties = new Properties();
properties.put(AdminClientConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9092");

AdminClient adminClient = AdminClient.create(properties);

ListTopicsOptions listTopicsOptions = new ListTopicsOptions();
listTopicsOptions.listInternal(true);

System.out.println(adminClient.listTopics(listTopicsOptions).names().get());

Lanita

Answer 3

I would prefer to use kafka-topics.sh which is a built in shell script of Kafka to get topics.

Prance

Hi Thanks for reply . I just want to do the same with API. – Mercurate

That shell script internally calls a Java (or Scala) class – Babbler

Answer 4

Kafka Client library has AdminClient API: which supports managing and inspecting topics, brokers, configurations, ACL’s.

You can find code samples for

• Creating new topic
• Delete topic
• Describe topic: gives Leader, Partitions, ISR and Replicas
• List topics
• Fetch controller broker/node details
• All brokers/nodes details from the cluster

https://medium.com/nerd-for-tech/how-client-application-interact-with-kafka-cluster-made-easy-with-java-apis-58f29229d992

Giffer