使用低级 Kafka Stream API 执行 context.forward() 时的 NPE [英] NPE while doing context.forward() using low-level Kafka Stream API

问题描述

我使用低级 Kafka API 构建了一个普通的 Kafka 流 API.拓扑是线性的.

I have built a plain Kafka streams API using Low-level Kafka API. The topology is linear.

p1 ->p2 ->p3

p1 -> p2 -> p3

在执行 context.forward() 时，我得到了 NPE，这里是片段:

While doing context.forward(), I am getting NPE, snippet here:

NAjava.lang.NullPointerException: null
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:178)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:133)

...

我使用的是 Kafka Stream 2.3.0.

I am using Kafka Stream 2.3.0.

我看到一个类似的 SO 问题 [here][1]，该问题基于非常旧的版本.那么，不确定这是否是相同的错误?

I see a similar SO question [here][1], and the question is based on the very old version. So, not sure if this is the same error?

我正在添加更多信息，保留我正在做的事情的要点

I am putting some more info, keeping the Gist of what I am doing

public class SP1Processor implements StreamProcessor {

private StreamProcessingContext ctxt;

// In init(), create a single thread pool
// which does some processing and sends the
// data to next processor
@Override
void init(StreamProcessingContext ctxt) {

      this.ctxt = ctxt;

     // Create a thread pool, do some work
     // and then do this.ctxt.forward(K,V)

    // Not showing code of Thread pool
    // Strangely, inside this thread pool,
    // this.ctxt isn't same what I see in process()
    // shouldn't it be same? ctxt is member variable
    // and shouldn't it be same
    // this.ctxt.forward(K,V) here in this thread pool is causing NPE
    // why does it happen?
    this.ctxt.forward(K,V);

}

@Override
void process(K,V) {

   // Here do some processing and go to the next processor chain
   // This works fine
   this.ctxt.forward(K,V);
}

}

  [1]: https://stackoverflow.com/questions/39067846/periodic-npe-in-kafka-streams-processor-context

推荐答案

看起来它可能与链接的问题是同一个问题，尽管我们在您的案例中讨论的是更现代的版本.确保 ProcessorSupplier.get() 每次调用时都会返回一个新实例.

It looks like it could be the same issue as the linked question, although we are talking about a much more contemporary version in your case. Make sure that ProcessorSupplier.get() returns a new instance each time it is called.

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