Subscription and polling

Consumer has to subscribe to some topic to receive data. The KafkaConsumer object has subscribe(), which takes a list of topics that the consumer wants to subscribe to. There are different forms of the subscribe method.

Let's talk about the subscribe method in detail with its different signatures:

• public void subscribe(Collection<String> topics): This signature takes a list of topic names to which the consumer wants to subscribe. It uses the default rebalancer, which may affect data processing of the message.

• public void subscribe(Pattern pattern,ConsumerRebalanceListener listener): This signature takes regex to match topics that exist in Kafka. This process is dynamic; any addition of a new topic matching the regex or deletion of a topic matching the regex will trigger the rebalancer. The second parameter, ConsumerRebalanceListener, will take your own class that implements this interface. We will talk about this in detail.

• public void subscribe(Collection<String> topics,ConsumerRebalanceListener listener): This takes a list of topics and your implementation of ConsumerRebalanceListner.