问题
I'm trying to create a leftJoin in Kafka Streams which works fine for about 10 Records and then it crashes with an exception caused by a NullPointerException with such code:
private static KafkaStreams getKafkaStreams() {
StreamsConfig streamsConfig = new StreamsConfig(getProperties());
KStreamBuilder builder = new KStreamBuilder();
KTable<String, Verkaeufer> umsatzTable = builder.table(Serdes.String(), EventstreamSerde.Verkaeufer(), CommonUtilsConstants.TOPIC_VERKAEUFER_STAMMDATEN);
KStream<String, String> verkaeuferStream = builder.stream(CommonUtilsConstants.TOPIC_ANZAHL_UMSATZ_PER_VERKAEUFER);
KStream<String, String> tuttiStream = verkaeuferStream.leftJoin(umsatzTable,
(tutti, verkaeufer) -> ("Vorname=" + verkaeufer.getVorname().toString() +",Nachname=" +verkaeufer.getNachname().toString() +"," +tutti.toString()), Serdes.String(), Serdes.String());
tuttiStream.to(Serdes.String(), Serdes.String(), CommonUtilsConstants.TOPIC_TUTTI);
return new KafkaStreams(builder, streamsConfig);
}
StreamsConfig looks like this:
private static Properties getProperties() {
Properties props = new Properties();
props.put(StreamsConfig.BOOTSTRAP_SERVERS_CONFIG, CommonUtilsConstants.BOOTSTRAP_SERVER_CONFIGURATION);
props.put(StreamsConfig.APPLICATION_ID_CONFIG, CommonUtilsConstants.GID_TUTTI);
props.put(StreamsConfig.DEFAULT_KEY_SERDE_CLASS_CONFIG, Serdes.String().getClass());
props.put(StreamsConfig.DEFAULT_VALUE_SERDE_CLASS_CONFIG,Serdes.String().getClass());
props.put(StreamsConfig.CACHE_MAX_BYTES_BUFFERING_CONFIG, "1000");
return props;
}
Full Stack Trace:
22:19:36.550 [gid-tutti-8fe6be58-d5c5-41ce-982d-88081b98004e-StreamThread-1] ERROR o.a.k.s.p.internals.StreamThread - stream-thread [gid-tutti-8fe6be58-d5c5-41ce-982d-88081b98004e-StreamThread-1] Failed to commit StreamTask 0_0 state: org.apache.kafka.streams.errors.ProcessorStateException: task [0_0] Failed to flush state store KTABLE-SOURCE-STATE-STORE-0000000000
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:262)
at org.apache.kafka.streams.processor.internals.AbstractTask.flushState(AbstractTask.java:190)
at org.apache.kafka.streams.processor.internals.StreamTask.flushState(StreamTask.java:282)
at org.apache.kafka.streams.processor.internals.StreamTask$1.run(StreamTask.java:264)
at org.apache.kafka.streams.processor.internals.StreamsMetricsImpl.measureLatencyNs(StreamsMetricsImpl.java:187)
at org.apache.kafka.streams.processor.internals.StreamTask.commitImpl(StreamTask.java:259)
at org.apache.kafka.streams.processor.internals.StreamTask.commit(StreamTask.java:253)
at org.apache.kafka.streams.processor.internals.StreamThread.commitOne(StreamThread.java:815)
at org.apache.kafka.streams.processor.internals.StreamThread.access$2800(StreamThread.java:73)
at org.apache.kafka.streams.processor.internals.StreamThread$2.apply(StreamThread.java:797)
at org.apache.kafka.streams.processor.internals.StreamThread.performOnStreamTasks(StreamThread.java:1448)
at org.apache.kafka.streams.processor.internals.StreamThread.commitAll(StreamThread.java:789)
at org.apache.kafka.streams.processor.internals.StreamThread.maybeCommit(StreamThread.java:778)
at org.apache.kafka.streams.processor.internals.StreamThread.runLoop(StreamThread.java:567)
at org.apache.kafka.streams.processor.internals.StreamThread.run(StreamThread.java:527) Caused by: java.lang.NullPointerException: null
at java.lang.String.<init>(String.java:143)
at ch.wesr.eventstream.commonutils.serde.GsonDeserializer.deserialize(GsonDeserializer.java:38)
at org.apache.kafka.streams.state.StateSerdes.valueFrom(StateSerdes.java:163)
at org.apache.kafka.streams.state.internals.CachingKeyValueStore.putAndMaybeForward(CachingKeyValueStore.java:90)
at org.apache.kafka.streams.state.internals.CachingKeyValueStore.access$000(CachingKeyValueStore.java:34)
at org.apache.kafka.streams.state.internals.CachingKeyValueStore$1.apply(CachingKeyValueStore.java:78)
at org.apache.kafka.streams.state.internals.NamedCache.flush(NamedCache.java:145)
at org.apache.kafka.streams.state.internals.NamedCache.flush(NamedCache.java:103)
at org.apache.kafka.streams.state.internals.ThreadCache.flush(ThreadCache.java:97)
at org.apache.kafka.streams.state.internals.CachingKeyValueStore.flush(CachingKeyValueStore.java:107)
at org.apache.kafka.streams.processor.internals.ProcessorStateManager.flush(ProcessorStateManager.java:260)
... 14 common frames omitted
Update:
This is what GsonDeserialize looks like
public class GsonDeserializer<T> implements Deserializer<T>{
public static final String CONFIG_VALUE_CLASS = "default.value.deserializer.class";
public static final String CONFIG_KEY_CLASS = "default.key.deserializer.class";
private Class<T> deserializedClass;
private Gson gson = new GsonBuilder().create();
public GsonDeserializer() {}
@Override
public void configure(Map<String, ?> config, boolean isKey) {
String configKey = isKey ? CONFIG_KEY_CLASS : CONFIG_VALUE_CLASS;
String clsName = String.valueOf(config.get(configKey));
try {
if (deserializedClass == null) {
deserializedClass = (Class<T>) Class.forName(clsName);
}
} catch (ClassNotFoundException e) {
System.err.printf("Failed to configure GsonDeserializer. " +
"Did you forget to specify the '%s' property ?%n",
configKey);
System.out.println(e.getMessage());
}
}
@Override
public T deserialize(String s, byte[] bytes) {
return gson.fromJson(new String(bytes), deserializedClass);
}
@Override
public void close() {}
}
回答1:
As long as the cache is not flushed, your deserializer is never called. That's why it doesn't fail in the beginning and you can increase the time until it fails via cache size parameter and commit interval (we flush on commit).
Looking at your code for GsonDeserializer, it seems that new String(bytes) fails with NPE -- String constructor cannot take null as parameter -- your deserializer code must guard against bytes==null and should return null for this case directly.
来源：https://stackoverflow.com/questions/46749155/failed-to-flush-state-store