java Kafka流转发方法引发NullPointerException,因为ProcessorNode currentNode对象为null
我们已经编写了Kafka流应用程序,它从源主题读取数据,并在2处理器中执行一些业务逻辑,然后将输出写入sink主题
下面是创建拓扑、添加源、处理器(请注意,我们正在添加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,我们会在下面的代码中得到null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。罐子 你能帮我找到我们失踪的地方吗。无法找出currentNode对象为Null的原因。 早期的帮助是非常感谢的
# 1 楼答案
根据代码:https://github.com/apache/kafka/blob/2.4/streams/src/main/java/org/apache/kafka/streams/processor/internals/ProcessorContextImpl.java#L183该错误意味着
currentNode()
返回null
这表示您违反了
ProcessorSupplier
的规则,在get()
上返回一个新的Processor
实例;当您将() -> fileExtractProcessorObject
传递给addProcessor
每次返回相同的对象引用时,这似乎保持不变,而您每次都需要通过() -> new FileExtractProcessor()
创建一个新实例我创建了一个票证来改进错误消息:https://issues.apache.org/jira/browse/KAFKA-10036