如何从 Transformer 输出多条记录？

Question

给定：具有 KStream::transform 的 DSL 拓扑。作为 Transformer::transform 执行的一部分，从输入消息 (KeyValue<String, Message>) 生成多条消息。

我可能可以 return KeyValue<String, List<Message>> 来自 Transformer::transform 的对象，并将 flatMapValues 应用为拓扑中的下一个处理器以使列表变平。但是我想知道是否可以将 ProcessorContext::forward 用于同一目标，即

public KeyValue<String, Message> transform(String key, Message message) {
        Iterable<Message> messages = generateMultipleFromOne(message);
        messages.forEach(m->context.forward(key, m));

        return null;
}

Answer 1

来自javadoc of Transformer.transform(K key, V value)：

If more than one output record should be forwarded downstream, ProcessorContext.forward(Object, Object) and ProcessorContext.forward(Object, Object, To) can be used.

Note that returning a new KeyValue is merely for convenience. The same can be achieved by using ProcessorContext.forward(Object, Object) and returning null.

如何从 Transformer 输出多条记录？

How to output multiple records from Transformer?

java

apache-kafka

apache-kafka-streams