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Streaming Data Using Kafka Streams to Count Words

Kafka Streams is a library enabling you to perform per-event processing of records. You can use it to process data as soon as it arrives, versus having to wait for a batch to occur. In this hands-on lab, we use Kafka Streams to stream some input data as plain-text and process it in real-time. With this, we can count the number of words from our input stream.

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Lab Info
Level
Intermediate
Last updated
Sep 19, 2025
Duration
1h 0m

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Table of Contents
  1. Challenge

    Create the Input and Output Topic

    Create the input topic named streams-plaintext-input.

    bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic streams-plaintext-input
    

    Create the output topic named streams-wordcount-output.

    bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic streams-wordcount-output
    
  2. Challenge

    Open a Kafka Console Producer

    Open a Kafka console producer.

    bin/kafka-console-producer.sh --broker-list localhost:9092 --topic streams-plaintext-input
    

    Type the three messages from the instructions.

    >kafka streams is great
    >kafka processes messages in real time
    >kafka helps real information streams
    
  3. Challenge

    Open a Kafka Console Consumer

    Open a Kafka console consumer using the default message formatter and the three properties given in the instructions.

    bin/kafka-console-consumer.sh --bootstrap-server localhost:9092 
    --topic streams-wordcount-output 
    --from-beginning 
    --formatter kafka.tools.DefaultMessageFormatter 
    --property print.key=true 
    --property print.value=true 
    --property key.deserializer=org.apache.kafka.common.serialization.StringDeserializer 
    --property value.deserializer=org.apache.kafka.common.serialization.LongDeserializer
    
  4. Challenge

    Run the Kafka Streams Application

    Use the kafka-run-class.sh command to run the WordCountDemo application.

    bin/kafka-run-class.sh org.apache.kafka.streams.examples.wordcount.WordCountDemo
    
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