java - KafkaStream.KTable如何以(压缩)KV风格将数据写入kafka主题

Question

在 Kafka(0.11.0.1) Streams 中，演示应用程序 Play with a Streams Application

// Serializers/deserializers (serde) for String and Long types
final Serde<String> stringSerde = Serdes.String();
final Serde<Long> longSerde = Serdes.Long();

// Construct a `KStream` from the input topic "streams-plaintext-input", where message values
// represent lines of text (for the sake of this example, we ignore whatever may be stored
// in the message keys).
KStream<String, String> textLines = builder.stream(stringSerde, stringSerde, "streams-plaintext-input");

KTable<String, Long> wordCounts = textLines
    // Split each text line, by whitespace, into words.
    .flatMapValues(value -> Arrays.asList(value.toLowerCase().split("\\W+")))

    // Group the text words as message keys
    .groupBy((key, value) -> value)

    // Count the occurrences of each word (message key).
    .count("Counts")

    // Store the running counts as a changelog stream to the output topic.
    wordCounts.to(stringSerde, longSerde, "streams-wordcount-output");

第5步，处理一些数据后，我们可以在接收器主题streams-wordcount-output中看到压缩的KV对(例如streams 2)，

> 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 

all     1 
streams 1 
lead    1 
to      1 
kafka   1 
hello   1 
kafka   2 
streams 2

问题是上面数据中的KTable wordCounts如何以Key-Value方式将数据写入主题streams-wordcount-output？

主题streams-wordcount-output的选项cleanup.policy似乎是默认值，delete，而不是compact (通过 bin/kafka-configs.sh)

Answer 1

所有输入和输出主题均“超出 Kafka Streams 的范围”。创建和配置这些主题是用户的责任。

因此，您的主题“streams-wordcount-output”将具有您在创建主题时指定的配置。

比照。 https://docs.confluent.io/current/streams/developer-guide.html#managing-topics-of-a-kafka-streams-application