Kafka Stream forward 方法拋出 NullPointerException 因為 ProcessorNode currentNode object 是 null

Question

我們編寫了 Kafka stream 應用程序，該應用程序從源主題讀取，在 2 個處理器中執行一些業務邏輯，然后將 output 寫入接收主題。

下面是創建拓撲、添加源、處理器（請注意我們添加 2 個處理器）和接收器的代碼

Topology topology = new Topology();
topology.addSource("sourceProcessor", "source-topic")
        .addProcessor("Process", ()->fileExtractProcessorObject , "sourceProcessor")
        .addProcessor("XMLJSON", () -> xmlJson , "Process")
        .addSink("sinkProcessor", "sink-topic", "XMLJSON");
KafkaStreams streams = new KafkaStreams(topology, getProperties(appConfig,sourceConfig));
        streams.start()

下面是第一個處理器代碼

public class FileExtractProcessor implements Processor<String, byte[]> {
    private ProcessorContext context;
    public FileExtractProcessor() {
    }

    @Override
    public void init(ProcessorContext context) {
        this.context = context;
    }

    @Override
    public void process(String key, byte[] bytearray) {
            /* business logic */

            //This is pojo class which will be forwarded to next processor as value
            ProcessData pData = new ProcessData();

                // Setting pojo object and forwarding to next processor
                pData.setValue(value);
                pData.setXmlData(files);
                pData.setAppconfig(ac);

                context.forward(value.getRunKeyId(), pData, To.child("XMLJSON"));
                context.commit();    
    }
}

在上面的代碼中，當我們調用 forward 方法時，我們在下面的代碼中得到 null 指針異常。

org.apache.kafka.streams.processor.internals.ProcessorContextImpl#forward(K, V, org.apache.kafka.streams.processor.To)

ProcessorNode child = this.currentNode().getChild(sendTo); 

java.lang.NullPointerException
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:183)
    at com.myapp.FileExtractProcessor.process(FileExtractProcessor.java:78)
    at com.myapp.FileExtractProcessor.process(FileExtractProcessor.java:22)
    at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:118)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:201)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:180)
    at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:133)
    at org.apache.kafka.streams.processor.internals.SourceNode.process(SourceNode.java:87)
    at org.apache.kafka.streams.processor.internals.StreamTask.process(StreamTask.java:429)
    at org.apache.kafka.streams.processor.internals.AssignedStreamsTasks.process(AssignedStreamsTasks.java:474)
    at org.apache.kafka.streams.processor.internals.TaskManager.process(TaskManager.java:536)
    at org.apache.kafka.streams.processor.internals.StreamThread.runOnce(StreamThread.java:792)
    at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:698)
    at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:671)

我們正在使用 kafka-stream-2.4.0.jar 能否請您幫助我們在這里缺少的地方。 無法弄清楚為什么 currentNode object 是 Null。 非常感謝早期幫助。

Answer 1

基於代碼： https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L183錯誤意味着currentNode()返回null 。

這表明您違反了ProcessorSupplier的規則，在get()上返回一個新的Processor實例； 當您將() -> fileExtractProcessorObject給addProcessor時，這似乎成立，每次都返回相同的 object 引用——相反，您每次都需要通過() -> new FileExtractProcessor()創建一個新實例。

我創建了一張票以改進錯誤消息： https://issues.apache.org/jira/browse/KAFKA-10036