Write JavaDStream to Kafka (how?)

[Gutwein, Sebastian]

Hi,


I'am new to Spark-Streaming and want to run some end-to-end-tests with Spark 
and Kafka.

My program is running but at the kafka topic nothing arrives. Can someone 
please help me?

Where is my mistake, has someone a runnig example of writing a DStream to Kafka 
0.10.1.0?


The program looks like follows:

import kafka.Kafka;
import org.apache.kafka.clients.producer.KafkaProducer;
import org.apache.kafka.clients.producer.ProducerConfig;
import org.apache.kafka.clients.producer.ProducerRecord;
import org.apache.spark.SparkConf;
import org.apache.spark.api.java.JavaPairRDD;
import org.apache.spark.api.java.JavaRDD;
import org.apache.spark.api.java.function.*;
import org.apache.spark.rdd.RDD;
import org.apache.spark.streaming.Duration;
import org.apache.spark.streaming.api.java.JavaDStream;
import org.apache.spark.streaming.api.java.JavaPairDStream;
import org.apache.spark.streaming.api.java.JavaPairReceiverInputDStream;
import org.apache.spark.streaming.api.java.JavaStreamingContext;
import org.apache.spark.streaming.kafka.KafkaUtils;
import scala.Int;
import scala.Tuple2;

import java.util.*;
import java.util.regex.Pattern;

/**
 * Consumes messages from one or more topics in Kafka and does wordcount.
 *
 * Usage: JavaKafkaWordCount <zkQuorum> <group> <topics> <numThreads>
 *   <zkQuorum> is a list of one or more zookeeper servers that make quorum
 *   <group> is the name of kafka consumer group
 *   <topics> is a list of one or more kafka topics to consume from
 *   <numThreads> is the number of threads the kafka consumer should use
 *
 * To run this example:
 *   `$ bin/run-example org.apache.spark.examples.streaming.JavaKafkaWordCount 
zoo01,zoo02, \
 *    zoo03 my-consumer-group topic1,topic2 1`
 */

public final class JavaKafkaWordCountTest {
  private static final Pattern SPACE = Pattern.compile(" ");

  private JavaKafkaWordCountTest() {
  }

  public static void main(String[] args) throws Exception {
    if (args.length < 4) {
      System.err.println("Usage: JavaKafkaWordCount <zkQuorum> <group> <topics> 
<numThreads>");
      System.exit(1);
    }

    SparkConf sparkConf = new SparkConf().setAppName("GutweinKafkaWordCount");
    // Create the context with 2 seconds batch size
    JavaStreamingContext jssc = new JavaStreamingContext(sparkConf, new 
Duration(2000));

    int numThreads = Integer.parseInt(args[3]);
    Map<String, Integer> topicMap = new HashMap<>();
    String[] topics = args[2].split(",");
    for (String topic: topics) {
      topicMap.put(topic, numThreads);
    }

    final JavaPairReceiverInputDStream<String, String> messages =
            KafkaUtils.createStream(jssc, args[0], args[1], topicMap);

    JavaDStream<String> lines = messages.map(new Function<Tuple2<String, 
String>, String>() {
      @Override
      public String call(Tuple2<String, String> tuple2) {
        return tuple2._2();
      }
    });

    JavaDStream<String> words = lines.flatMap(new FlatMapFunction<String, 
String>() {
      @Override
      public Iterator<String> call(String x) {
        return Arrays.asList(SPACE.split(x)).iterator();
      }
    });

    JavaPairDStream<String, Integer> wordCounts = words.mapToPair(
      new PairFunction<String, String, Integer>() {
        @Override
        public Tuple2<String, Integer> call(String s) {
          return new Tuple2<>(s, 1);
        }
      }).reduceByKey(new Function2<Integer, Integer, Integer>() {
        @Override
        public Integer call(Integer i1, Integer i2) {
          return i1 + i2;
        }
      });

    final KafkaWriter writer = new KafkaWriter("localhost:9081");

    wordCounts.foreachRDD(new VoidFunction<JavaPairRDD<String, Integer>>() {
        @Override
        public void call(JavaPairRDD<String, Integer> stringIntegerJavaPairRDD) 
throws Exception {
            writer.writeToTopic("output", stringIntegerJavaPairRDD.toString());
        }
    });

    wordCounts.print();
    jssc.start();
    jssc.awaitTermination();
  }

  public static class KafkaWriter {
    Properties props = new Properties();
    KafkaProducer<String, String> producer;

    // Constructor
    KafkaWriter(String bootstrap_server){
      props.put(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, bootstrap_server);
      props.put(ProducerConfig.KEY_SERIALIZER_CLASS_CONFIG, 
"org.apache.kafka.common.serialization.StringSerializer");
      props.put(ProducerConfig.VALUE_SERIALIZER_CLASS_CONFIG, 
"org.apache.kafka.common.serialization.StringSerializer");
      producer = new KafkaProducer<String, String>(props);
    }


    private void writeToTopic(String topicName, String message){
      ProducerRecord<String, String> record = new ProducerRecord<>(topicName, 
message);
      producer.send(record);

    }

  }

}