java - Kafka Streams SessionWindows 中的节流

Question

默认情况下，.windowsedBy(SessionWindows.with(...)) 将返回每个新的传入记录。那么，我如何才能等待至少 1 秒才能返回当前 session 窗口的最后一个结果？

我正在尝试使用字数统计示例:

        final KStream<String, String> source = builder.stream("streams-plaintext-input");

        final KStream<String, Long> wordCounts = source

                // Split each text line, by whitespace, into words.
                .flatMapValues(value -> Arrays.asList(value.toLowerCase(Locale.getDefault()).split(" ")))

                // Group the stream by word to ensure the key of the record is the word.
                .groupBy((key, word) -> word)

                .windowedBy(SessionWindows.with(Duration.ofSeconds(10)))

                // Count the occurrences of each word (message key).
                .count(Materialized.with(Serdes.String(), Serdes.Long()))

                .suppress(Suppressed.untilTimeLimit(Duration.ofSeconds(1), Suppressed.BufferConfig.unbounded()))

                // Convert to KStream<String, Long>
                .toStream((windowedId, count) -> windowedId.key());

        wordCounts.foreach((word, count) -> {
            System.out.println(word + " : " + count);
        });

这是producer的input和client的result，其实是错误的:

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

(nothing)

>hello kafka stream

hello : 1
kafka : 1
stream : 1

>hello kafka stream

hello : null
kafka : 1
stream : 1

我该如何解决？非常感谢阅读我的问题:)

Answer 1

KTable#suppress() 运算符是您在这种情况下的 friend 。

查看文档和有关它的详细博客文章:

• https://kafka.apache.org/22/documentation/streams/developer-guide/dsl-api.html 中的“控制 KTABLE 发射率”部分
• 或https://kafka.apache.org/22/documentation/streams/developer-guide/dsl-api.html#window-final-results
• https://www.confluent.io/blog/kafka-streams-take-on-watermarks-and-triggers