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

The only way that comes to mind for this from a consumer point of view is to actually consume the messages and count them then.

The Kafka broker exposes JMX counters for number of messages received since start-up but you cannot know how many of them have been purged already.

In most common scenarios, messages in Kafka is best seen as an infinite stream and getting a discrete value of how many that is currently being kept on disk is not relevant. Furthermore things get more complicated when dealing with a cluster of brokers which all have a subset of the messages in a topic.

It is not java, but may be useful

./bin/kafka-run-class.sh kafka.tools.GetOffsetShell \
  --broker-list <broker>:<port> \
  --topic <topic-name> \
  | awk -F  ":" '{sum += $3} END {print sum}'