我有一个处理器，该处理器从主题获取json字符串，类型为GenericRecord。 现在我将流分成2个分支。 我进入第一个分支，然后将（键，值）映射到2个字符串中，该字符串包含json的特定字段和该字段的值，并且按键分组。 到目前为止，一切都很好。 现在，我必须使用新的Type用户定义来聚合流，并且会收到异常。
代码在这里：
新类型：
private class Tuple {
public int occ;
public int sum;
public Tuple (int occ, int sum) {
this.occ = occ;
this.sum = sum;
}
public void sum (int toAdd) {
this.sum += toAdd;
this.occ ++;
}
public int getAverage () {
return this.sum / this.occ;
}
public String toString() {
return occ + "-> " + sum + ": " + getAverage();
}
好的流：
StreamsBuilder builder = new StreamsBuilder();
KStream<GenericRecord, GenericRecord> source =
builder.stream(topic);
KStream<GenericRecord, GenericRecord>[] branches = source.branch(
(key,value) -> partition(value.toString()),
(key, value) -> true
);
KGroupedStream <String, String> groupedStream = branches[0]
.mapValues(value -> createJson(value.toString()))
.map((key, value) -> KeyValue.pair(new String("T_DUR_CICLO"), value.getNumberValue("payload", "T_DUR_CICLO")))
.peek((key, value) -> System.out.println("key=" + key + ", value=" + value))
.groupByKey();
问题：
KTable<String, Tuple> aggregatedStream = groupedStream.aggregate(
() -> new Tuple (0,0), // initializer
(aggKey, newValue, aggValue) -> new Tuple (aggValue.occ + 1, aggValue.sum + Integer.parseInt(newValue)));
KafkaStreams streams = new KafkaStreams(builder.build(), props);
streams.start();
这是例外：
Exception in thread "streamtest-6173d6a2-4a3a-4d76-b793-774719f8b1f5-StreamThread-1" org.apache.kafka.streams.errors.StreamsException: Exception caught in process. taskId=1_0, processor=KSTREAM-SOURCE-0000000011, topic=streamtest-KSTREAM-AGGREGATE-STATE-STORE-0000000007-repartition, partition=0, offset=0
at org.apache.kafka.streams.processor.internals.StreamTask.process(StreamTask.java:318)
at org.apache.kafka.streams.processor.internals.AssignedStreamsTasks.process(AssignedStreamsTasks.java:94)
at org.apache.kafka.streams.processor.internals.TaskManager.process(TaskManager.java:409)
at org.apache.kafka.streams.processor.internals.StreamThread.processAndMaybeCommit(StreamThread.java:964)
at org.apache.kafka.streams.processor.internals.StreamThread.runOnce(StreamThread.java:832)
at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:767)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:736)
Caused by: org.apache.kafka.streams.errors.StreamsException: A serializer (value: io.confluent.kafka.streams.serdes.avro.GenericAvroSerializer) is not compatible to the actual value type (value type: com.mycompany.maventest.Streamer$Tuple). Change the default Serdes in StreamConfig or provide correct Serdes via method parameters.
at org.apache.kafka.streams.state.StateSerdes.rawValue(StateSerdes.java:195)
at org.apache.kafka.streams.state.internals.MeteredKeyValueBytesStore$1.innerValue(MeteredKeyValueBytesStore.java:66)
at org.apache.kafka.streams.state.internals.MeteredKeyValueBytesStore$1.innerValue(MeteredKeyValueBytesStore.java:57)
at org.apache.kafka.streams.state.internals.InnerMeteredKeyValueStore.put(InnerMeteredKeyValueStore.java:206)
at org.apache.kafka.streams.state.internals.MeteredKeyValueBytesStore.put(MeteredKeyValueBytesStore.java:117)
at org.apache.kafka.streams.kstream.internals.KStreamAggregate$KStreamAggregateProcessor.process(KStreamAggregate.java:94)
at org.apache.kafka.streams.processor.internals.ProcessorNode$1.run(ProcessorNode.java:50)
at org.apache.kafka.streams.processor.internals.ProcessorNode.runAndMeasureLatency(ProcessorNode.java:244)
at org.apache.kafka.streams.processor.internals.ProcessorNode.process(ProcessorNode.java:133)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:143)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:126)
at org.apache.kafka.streams.processor.internals.ProcessorContextImpl.forward(ProcessorContextImpl.java:90)
at org.apache.kafka.streams.processor.internals.SourceNode.process(SourceNode.java:87)
at org.apache.kafka.streams.processor.internals.StreamTask.process(StreamTask.java:302)
... 6 more
Caused by: java.lang.ClassCastException: com.mycompany.maventest.Streamer$Tuple cannot be cast to org.apache.avro.generic.GenericRecord
at io.confluent.kafka.streams.serdes.avro.GenericAvroSerializer.serialize(GenericAvroSerializer.java:39)
at org.apache.kafka.streams.state.StateSerdes.rawValue(StateSerdes.java:191)
... 19 more
我该如何解决？
-----更新------
生产者使用Avro进行生产，因此我具有以下配置属性：
props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, GenericAvroSerde.class);
props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG, GenericAvroSerde.class);
如果我指定自定义Serde，这就是结果：
KTable<String, Tuple> aggregatedStream = groupedStream.aggregate(
() -> new Tuple(0, 0), // initializer
(aggKey, newValue, aggValue) -> new Tuple (aggValue.occ + 1, aggValue.sum + Integer.parseInt(newValue)),
Materialized.with(Serdes.String(), new MySerde()));
例外：
Exception in thread "streamtest-17deb5c8-ed07-4fcf-bd59-37b75e44b83f-StreamThread-1" org.apache.kafka.streams.errors.StreamsException: Deserialization exception handler is set to fail upon a deserialization error. If you would rather have the streaming pipeline continue after a deserialization error, please set the default.deserialization.exception.handler appropriately.
at org.apache.kafka.streams.processor.internals.RecordDeserializer.deserialize(RecordDeserializer.java:80)
at org.apache.kafka.streams.processor.internals.RecordQueue.addRawRecords(RecordQueue.java:97)
at org.apache.kafka.streams.processor.internals.PartitionGroup.addRawRecords(PartitionGroup.java:117)
at org.apache.kafka.streams.processor.internals.StreamTask.addRecords(StreamTask.java:677)
at org.apache.kafka.streams.processor.internals.StreamThread.addRecordsToTasks(StreamThread.java:943)
at org.apache.kafka.streams.processor.internals.StreamThread.runOnce(StreamThread.java:831)
at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:767)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:736)
Caused by: org.apache.kafka.common.errors.SerializationException: Error deserializing Avro message for id -1
Caused by: org.apache.kafka.common.errors.SerializationException: Unknown magic byte!
---解决了---- 我还为groupBy
中的类型更改添加了新的Serde。 KGroupedStream <String, String> groupedStream = branches[0]
.mapValues(value -> createJson(value.toString()))
.map((key, value) -> KeyValue.pair(new String("T_DUR_CICLO"), value.getNumberValue("payload", "T_DUR_CICLO")))
.peek((key, value) -> System.out.println("key=" + key + ", value=" + value))
.groupByKey( Serialized.with(
Serdes.String(), /* key (note: type was modified) */
Serdes.String())); /* value */
答案 0 :(得分：1)
除非使用操作明确指定，否则Kafka流将使用默认的Serde。
在aggregate（）方法中，您将valueType定义为Tuple，而默认serde用于GenericRecord，因此会引发异常。您需要指定serde，如下所示：
KTable<String, Tuple> aggregatedStream = groupedStream.aggregate(
() -> new Tuple (0,0), // initializer
(aggKey, newValue, aggValue) ->
new Tuple (aggValue.occ + 1, aggValue.sum + Integer.parseInt(newValue))
,Materialized.with(keySerde, tupleSerde));
它将使用tupleSerde进行此操作。您可以在此处找到示例： https://docs.confluent.io/current/streams/developer-guide/dsl-api.html#aggregating