src-kafka/docs/streams/index.html

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    <h1>Kafka Streams API</h1>

    <h3 style="max-width: 75rem;">The easiest way to write mission-critical real-time applications and microservices with all the benefits of Kafka's server-side cluster technology.</h3>

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            <a href="/{{version}}/documentation/streams/tutorial" class="btn">Write your first app</a>
            <a href="/{{version}}/documentation/streams/quickstart" class="btn">Play with demo app</a>
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    <ul class="feature-list">
        <li>Write standard Java applications</li>
        <li>Exactly-once processing semantics</li>
        <li>No seperate processing cluster required</li>
        <li>Develop on Mac, Linux, Windows</li>
        <li>Elastic, highly scalable, fault-tolerant</li>
        <li>Deploy to containers, VMs, bare metal, cloud</li>
        <li>Equally viable for small, medium, &amp; large use cases</li>
        <li>Fully integrated with Kafka security</li>
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    <h3>Hello Kafka Streams</h3>
    <p>The code example below implements a WordCount application that is elastic, highly scalable, fault-tolerant, stateful, and ready to run in production at large scale</p>

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        <div class="code-example__snippet b-java-8 selected">
            <pre class="brush: java;">
                import org.apache.kafka.common.serialization.Serdes;
                import org.apache.kafka.streams.KafkaStreams;
                import org.apache.kafka.streams.StreamsBuilder;
                import org.apache.kafka.streams.StreamsConfig;
                import org.apache.kafka.streams.kstream.KStream;
                import org.apache.kafka.streams.kstream.KTable;

                import java.util.Arrays;
                import java.util.Properties;

                public class WordCountApplication {

                    public static void main(final String[] args) throws Exception {
                        Properties config = new Properties();
                        config.put(StreamsConfig.APPLICATION_ID_CONFIG, "wordcount-application");
                        config.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "kafka-broker1:9092");
                        config.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
                        config.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());

                        KStreamBuilder builder = new KStreamBuilder();
                        KStream&lt;String, String&gt; textLines = builder.stream("TextLinesTopic");
                        KTable&lt;String, Long&gt; wordCounts = textLines
                            .flatMapValues(textLine -> Arrays.asList(textLine.toLowerCase().split("\\W+")))
                            .groupBy((key, word) -> word)
                            .count("Counts");
                        wordCounts.to(Serdes.String(), Serdes.Long(), "WordsWithCountsTopic");

                        KafkaStreams streams = new KafkaStreams(builder.build(), config);
                        streams.start();
                    }

                }
            </pre>
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            <pre class="brush: java;">
                import org.apache.kafka.common.serialization.Serdes;
                import org.apache.kafka.streams.KafkaStreams;
                import org.apache.kafka.streams.StreamsBuilder;
                import org.apache.kafka.streams.StreamsConfig;
                import org.apache.kafka.streams.kstream.KStream;
                import org.apache.kafka.streams.kstream.KTable;
                import org.apache.kafka.streams.kstream.KeyValueMapper;
                import org.apache.kafka.streams.kstream.ValueMapper;

                import java.util.Arrays;
                import java.util.Properties;

                public class WordCountApplication {

                    public static void main(final String[] args) throws Exception {
                        Properties config = new Properties();
                        config.put(StreamsConfig.APPLICATION_ID_CONFIG, "wordcount-application");
                        config.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "kafka-broker1:9092");
                        config.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
                        config.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass());

                        KStreamBuilder builder = new KStreamBuilder();
                        KStream&lt;String, String&gt; textLines = builder.stream("TextLinesTopic");
                        KTable&lt;String, Long&gt; wordCounts = textLines
                            .flatMapValues(new ValueMapper&lt;String, Iterable&lt;String&gt;&gt;() {
                                @Override
                                public Iterable&lt;String&gt; apply(String textLine) {
                                    return Arrays.asList(textLine.toLowerCase().split("\\W+"));
                                }
                            })
                            .groupBy(new KeyValueMapper&lt;String, String, String&gt;() {
                                @Override
                                public String apply(String key, String word) {
                                    return word;
                                }
                            })
                            .count("Counts");
                        wordCounts.to(Serdes.String(), Serdes.Long(), "WordsWithCountsTopic");

                        KafkaStreams streams = new KafkaStreams(builder, config);
                        streams.start();
                    }

                }
            </pre>
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        <div class="code-example__snippet b-scala">
            <pre class="brush: scala;">
                import java.lang.Long
                import java.util.Properties
                import java.util.concurrent.TimeUnit

                import org.apache.kafka.common.serialization._
                import org.apache.kafka.streams._
                import org.apache.kafka.streams.kstream.{KStream, KStreamBuilder, KTable}

                import scala.collection.JavaConverters.asJavaIterableConverter

                object WordCountApplication {

                    def main(args: Array[String]) {
                        val config: Properties = {
                            val p = new Properties()
                            p.put(StreamsConfig.APPLICATION_ID_CONFIG, "wordcount-application")
                            p.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, "kafka-broker1:9092")
                            p.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass)
                            p.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, Serdes.String().getClass)
                            p
                        }

                        val builder: KStreamBuilder = new KStreamBuilder()
                        val textLines: KStream[String, String] = builder.stream("TextLinesTopic")
                        val wordCounts: KTable[String, Long] = textLines
                            .flatMapValues(textLine => textLine.toLowerCase.split("\\W+").toIterable.asJava)
                            .groupBy((_, word) => word)
                            .count("Counts")
                        wordCounts.to(Serdes.String(), Serdes.Long(), "WordsWithCountsTopic")

                        val streams: KafkaStreams = new KafkaStreams(builder, config)
                        streams.start()

                        Runtime.getRuntime.addShutdownHook(new Thread(() => {
                            streams.close(10, TimeUnit.SECONDS)
                        }))
                    }

                }
            </pre>
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    <h3 class="customer-title">See how Kafka Streams is being used</h3>
    <div class="customer__cards">
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            <img src="/{{version}}/images/icons/NYT.jpg" style="max-width:35%">
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          <span class="customer__card__label">The New York Times uses Apache Kafka and the Kafka Streams API to store and distribute, in real-time, published content to the various applications and systems that make it available to the readers.</span>
            <a href="https://www.confluent.io/blog/publishing-apache-kafka-new-york-times/">Learn More</a>
             
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         <div class="customer__card customer-right" >
            <div class="customer__card__icon">
                 <img style="max-width:60%" src="../../images/powered-by/rabobank.jpg">
             </div>  
             <span class="customer__card__label">Rabobank is one of the 3 largest banks in the Netherlands. Its digital nervous system, the Business Event Bus, is powered by Apache Kafka. It is used by an increasing amount of financial processes and services, one which is Rabo Alerts. This service alerts customers in real-time upon financial events and is built using Kafka Streams.
             </span>
             <a href="https://www.confluent.io/blog/real-time-financial-alerts-rabobank-apache-kafkas-streams-api/">Learn More</a> 
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           <div class="customer__card__icon" >
                 <img style="max-width:60%"  src="../../images/powered-by/zalando.jpg">
              </div>  
              <span class="customer__card__label">As the leading online fashion retailer in Europe, Zalando uses Apache Kafka as an ESB (Enterprise Service Bus), which helps us in transitioning from a monolithic to a micro services architecture. Using Kafka for processing event streams enables our technical team to do near-real time business intelligence.</span>
              <a href="https://kafka-summit.org/sessions/using-kstreams-ktables-calculate-real-time-domain-rankings/">Learn More</a>
        </div>
        <div class="customer__card">
          <div class="customer__card__icon green_card">
            <img src="/{{version}}/images/icons/line.png">
          </div>  
          <span class="customer__card__label">LINE uses Apache Kafka as a central datahub for our services to communicate to one another. Hundreds of billions of messages are produced daily and are used to execute various business logic, threat detection, search indexing and data analysis. LINE leverages Kafka Streams to reliably transform and filter topics enabling sub topics consumers can efficiently consume, meanwhile retaining easy maintainability thanks to its sophisticated yet minimal code base.</span>
          <a href="https://engineering.linecorp.com/en/blog/detail/80">Learn More</a>
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