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java - Kafka Stream forward方法抛出NullPointerException，因为ProcessorNode currentNode对象为null

问题描述

我们已经编写了从源主题读取的 Kafka 流应用程序，它在 2 个处理器中执行一些业务逻辑，然后将输出写入接收主题。

下面是创建拓扑、添加源、处理器（请注意我们添加 2 个处理器）和接收器的代码

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()

下面是第一个处理器代码

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();    
    }
}

在上面的代码中，当我们调用 forward 方法时，我们在下面的代码中得到空指针异常。

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)

我们正在使用 kafka-stream-2.4.0.jar 能否请您帮助我们在这里缺少的地方。无法弄清楚为什么 currentNode 对象为 Null。非常感谢早期帮助。

标签： javaapache-kafkaapache-kafka-streamstopology

解决方案

基于代码：https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L183错误意味着currentNode()返回null。

这表明您违反了在;上ProcessorSupplier返回新Processor实例的规则。当您传递到每次返回相同的对象引用时get()，这似乎成立——相反，您每次都需要通过.() -> fileExtractProcessorObjectaddProcessor() -> new FileExtractProcessor()

我创建了一张票来改进错误消息：https ://issues.apache.org/jira/browse/KAFKA-10036

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