Code review comment: Where does this value come from? Could you add a little more context in the comment? (Same comment applies to withTopicPartitions argument below)

Code under review:
public static void main(String[] args) {
    final PipelineOptions options = PipelineOptionsFactory.create();
    final Pipeline p = Pipeline.create(options);

    final Map<String, Object> consumerConfig = new HashMap<>();
    consumerConfig.put("auto.offset.reset", "earliest");

    p.apply(
            KafkaIO.<Long, String>read()
                .withBootstrapServers(
                    "kafka_server:9092") 
                
                .withTopicPartitions(
                    Collections.singletonList(
                        new TopicPartition(
                            "dataset",
                            0))) 
                
                .withKeyDeserializer(LongDeserializer.class)
                .withValueDeserializer(StringDeserializer.class)
                .withConsumerConfigUpdates(consumerConfig)
                .withMaxNumRecords(5)
                .withoutMetadata())
        .apply(Values.create())
        .apply(
            "ExtractWords",
            ParDo.of(
                new DoFn<String, String>() {
                  @ProcessElement
                  public void processElement(ProcessContext c) {
                    for (String word : c.element().split(TOKENIZER_PATTERN, 0)) {
                      if (!word.isEmpty()) {
                        c.output(word);
                      }
                    }
                  }
                }))
        .apply(Count.perElement())
        .apply(
            "FormatResults",
            MapElements.via(
                new SimpleFunction<KV<String, Long>, String>() {
                  @Override
                  public String apply(KV<String, Long> input) {
                    System.out.printf("key: %s, value: %d%n", input.getKey(), input.getValue());
                    return input.getKey() + ": " + input.getValue();
                  }
                }))
        .apply(TextIO.write().to("word-counts"));

    p.run().waitUntilFinish();
  }

Line commented on: "kafka_server:9092")

Revised code:
public static void main(String[] args) {
    final PipelineOptions options = PipelineOptionsFactory.create();
    final Pipeline p = Pipeline.create(options);

    final Map<String, Object> consumerConfig = new HashMap<>();
    consumerConfig.put("auto.offset.reset", "earliest");

    p.apply(
            KafkaIO.<Long, String>read()
                .withBootstrapServers(
                    "kafka_server:9092") 
                
                
                .withTopicPartitions(
                    Collections.singletonList(
                        new TopicPartition(
                            "dataset",
                            0))) 
                
                
                .withKeyDeserializer(LongDeserializer.class)
                .withValueDeserializer(StringDeserializer.class)
                .withConsumerConfigUpdates(consumerConfig)
                .withMaxNumRecords(5)
                .withoutMetadata())
        .apply(Values.create())
        .apply(
            "ExtractWords",
            ParDo.of(
                new DoFn<String, String>() {
                  @ProcessElement
                  public void processElement(ProcessContext c) {
                    for (String word : c.element().split(TOKENIZER_PATTERN, 0)) {
                      if (!word.isEmpty()) {
                        c.output(word);
                      }
                    }
                  }
                }))
        .apply(Count.perElement())
        .apply(
            "FormatResults",
            MapElements.via(
                new SimpleFunction<KV<String, Long>, String>() {
                  @Override
                  public String apply(KV<String, Long> input) {
                    System.out.printf("key: %s, value: %d%n", input.getKey(), input.getValue());
                    return input.getKey() + ": " + input.getValue();
                  }
                }))
        .apply(TextIO.write().to("word-counts"));

    p.run().waitUntilFinish();
  }