java - 如何从 Transformer 输出多条记录？

Question

给定:带有 KStream::transform 的 DSL 拓扑.作为 Transformer::transform 的一部分执行多条消息从输入( KeyValue<String, Message> )生成。

我大概可以返回 KeyValue<String, List<Message>>来自 Transformer::transform 的对象并申请 flatMapValues作为拓扑中的下一个处理器来扁平化列表。但是我想知道是否可以使用 ProcessorContext::forward为了同一个目标，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) andProcessorContext.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.