问题描述
添加（& ）在使用Kafka Streams处理主题时是否可以获得这些标题？在 KStream 上调用 map 等方法时，它提供了键的参数和记录的值但我无法看到访问标题。如果我们只能 map 而不是 ConsumerRecord ，那就太好了。
With the addition of Headers to the records (ProducerRecord & ConsumerRecord) in Kafka 0.11, is it possible to get these headers when processing a topic with Kafka Streams? When calling methods like map on a KStream it provides arguments of the key and the value of the record but no way I can see to access the headers. It would be nice if we could just map over the ConsumerRecords.
ex。
KStreamBuilder kStreamBuilder = new KStreamBuilder();
KStream<String, String> stream = kStreamBuilder.stream("some-topic");
stream
.map((key, value) -> ... ) // can I get access to headers in methods like map, filter, aggregate, etc?
...
这样的事情会起作用：
KStreamBuilder kStreamBuilder = new KStreamBuilder();
KStream<String, String> stream = kStreamBuilder.stream("some-topic");
stream
.map((record) -> {
record.headers();
record.key();
record.value();
})
...
推荐答案
自Streams API的2.0版以来，可以访问记录标题。 （参见了解详情。）
Records headers are accessible since versions 2.0 of Streams API. (Cf. KIP-244 for details.)
您可以通过处理器API访问记录元数据（即通过转换（）， transformValues（），或 process（）），由给定的上下文对象（参见）。
You can access record metadata via Processor API (ie, via transform(), transformValues(), or process()), by the given "context" object (cf. https://docs.confluent.io/current/streams/developer-guide/processor-api.html#accessing-processor-context).
之前2.0，上下文只公开主题，分区，偏移量和时间戳---但不是那些在旧版本中读取时被Streams删除的标题。
Prior to 2.0, the context only exposes topic, partition, offset, and timestamp---but not headers that are in fact dropped by Streams on read in those older versions.
元数据虽然在DSL级别不可用。但是，还在进行扩展DSL的工作：
Metadata is not available at DSL level though. However, there is also work in progress to extend the DSL: https://cwiki.apache.org/confluence/display/KAFKA/KIP-159%3A+Introducing+Rich+functions+to+Streams
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