Apache Flink: Could not extract key from ObjectNode::get - json

Question

I'm using Flink to process the data coming from some data source (such as Kafka, Pravega etc).
In my case, the data source is Pravega, which provided me a flink connector.
My data source is sending me some JSON data as below:
{"device":"rand-numeric","id":"b4728895-741f-466a-b87b-79c7590893b4","origin":"1591095418904441036","readings":[{"origin":"1591095418904328442","valueType":"Int64","name":"int","device":"rand-numeric","value":"0"}]}
Here is my piece of code:
import org.apache.flink.shaded.jackson2.com.fasterxml.jackson.databind.node.ObjectNode;
PravegaDeserializationSchema<ObjectNode> adapter = new PravegaDeserializationSchema<>(ObjectNode.class, new JavaSerializer<>());
FlinkPravegaReader<ObjectNode> source = FlinkPravegaReader.<ObjectNode>builder()
.withPravegaConfig(pravegaConfig)
.forStream(stream)
.withDeserializationSchema(adapter)
.build();
final StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
DataStream<ObjectNode> dataStream = env.addSource(source).name("Pravega Stream");
dataStream.keyBy(new KeySelector<ObjectNode, String>() {
#Override
public String getKey(ObjectNode node) throws Exception {
return node.get("id").asText();
}
}).print();
env.execute("StreamingJob");
As you see, I used the FlinkPravegaReader and a proper deserializer to get the JSON stream coming from Pravega.
Then I try to KeyBy it with a custom KeySelector and print it.
However, I get an error:
Caused by: java.lang.RuntimeException: Could not extract key from
{"device":"rand-numeric","id":"b4728895-741f-466a-b87b-79c7590893b4","origin":"1591095418904441036","readings":[{"origin":"1591095418904328442","valueType":"Int64","name":"int","device":"rand-numeric","value":"0"}]}
It seems that node.get("id").asText(); threw this exception.
I don't know why. As we see there does exist a key named id in the JSON data. Why can't it be extracted? Have I used the class ObjectNode wrongly or some other reason?
Stack-trace:
org.apache.flink.client.program.ProgramInvocationException: The main method caused an error: org.apache.flink.client.program.ProgramInvocationException: Job failed (JobID: fa9846e6834ae1391acbf51d5ad35aac)
at org.apache.flink.client.program.PackagedProgram.callMainMethod(PackagedProgram.java:335)
at org.apache.flink.client.program.PackagedProgram.invokeInteractiveModeForExecution(PackagedProgram.java:205)
at org.apache.flink.client.ClientUtils.executeProgram(ClientUtils.java:138)
at org.apache.flink.client.cli.CliFrontend.executeProgram(CliFrontend.java:662)
at org.apache.flink.client.cli.CliFrontend.run(CliFrontend.java:210)
at org.apache.flink.client.cli.CliFrontend.parseParameters(CliFrontend.java:893)
at org.apache.flink.client.cli.CliFrontend.lambda$main$10(CliFrontend.java:966)
at org.apache.flink.runtime.security.NoOpSecurityContext.runSecured(NoOpSecurityContext.java:30)
at org.apache.flink.client.cli.CliFrontend.main(CliFrontend.java:966)
Caused by: java.util.concurrent.ExecutionException: org.apache.flink.client.program.ProgramInvocationException: Job failed (JobID: fa9846e6834ae1391acbf51d5ad35aac)
at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1908)
at org.apache.flink.streaming.api.environment.StreamContextEnvironment.execute(StreamContextEnvironment.java:83)
at org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.execute(StreamExecutionEnvironment.java:1620)
at myflink.StreamingJob.main(StreamingJob.java:137)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.flink.client.program.PackagedProgram.callMainMethod(PackagedProgram.java:321)
... 8 more
Caused by: org.apache.flink.client.program.ProgramInvocationException: Job failed (JobID: fa9846e6834ae1391acbf51d5ad35aac)
at org.apache.flink.client.deployment.ClusterClientJobClientAdapter.lambda$null$6(ClusterClientJobClientAdapter.java:112)
at java.util.concurrent.CompletableFuture.uniApply(CompletableFuture.java:616)
at java.util.concurrent.CompletableFuture$UniApply.tryFire(CompletableFuture.java:591)
at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:488)
at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1975)
at org.apache.flink.client.program.rest.RestClusterClient.lambda$pollResourceAsync$21(RestClusterClient.java:565)
at java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:774)
at java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:750)
at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:488)
at java.util.concurrent.CompletableFuture.complete(CompletableFuture.java:1975)
at org.apache.flink.runtime.concurrent.FutureUtils.lambda$retryOperationWithDelay$8(FutureUtils.java:291)
at java.util.concurrent.CompletableFuture.uniWhenComplete(CompletableFuture.java:774)
at java.util.concurrent.CompletableFuture$UniWhenComplete.tryFire(CompletableFuture.java:750)
at java.util.concurrent.CompletableFuture.postComplete(CompletableFuture.java:488)
at java.util.concurrent.CompletableFuture.postFire(CompletableFuture.java:575)
at java.util.concurrent.CompletableFuture$UniCompose.tryFire(CompletableFuture.java:943)
at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:456)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.flink.runtime.client.JobExecutionException: Job execution failed.
at org.apache.flink.runtime.jobmaster.JobResult.toJobExecutionResult(JobResult.java:147)
at org.apache.flink.client.deployment.ClusterClientJobClientAdapter.lambda$null$6(ClusterClientJobClientAdapter.java:110)
... 19 more
Caused by: org.apache.flink.runtime.JobException: Recovery is suppressed by NoRestartBackoffTimeStrategy
at org.apache.flink.runtime.executiongraph.failover.flip1.ExecutionFailureHandler.handleFailure(ExecutionFailureHandler.java:110)
at org.apache.flink.runtime.executiongraph.failover.flip1.ExecutionFailureHandler.getFailureHandlingResult(ExecutionFailureHandler.java:76)
at org.apache.flink.runtime.scheduler.DefaultScheduler.handleTaskFailure(DefaultScheduler.java:192)
at org.apache.flink.runtime.scheduler.DefaultScheduler.maybeHandleTaskFailure(DefaultScheduler.java:186)
at org.apache.flink.runtime.scheduler.DefaultScheduler.updateTaskExecutionStateInternal(DefaultScheduler.java:180)
at org.apache.flink.runtime.scheduler.SchedulerBase.updateTaskExecutionState(SchedulerBase.java:496)
at org.apache.flink.runtime.jobmaster.JobMaster.updateTaskExecutionState(JobMaster.java:380)
at sun.reflect.GeneratedMethodAccessor77.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.handleRpcInvocation(AkkaRpcActor.java:284)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.handleRpcMessage(AkkaRpcActor.java:199)
at org.apache.flink.runtime.rpc.akka.FencedAkkaRpcActor.handleRpcMessage(FencedAkkaRpcActor.java:74)
at org.apache.flink.runtime.rpc.akka.AkkaRpcActor.handleMessage(AkkaRpcActor.java:152)
at akka.japi.pf.UnitCaseStatement.apply(CaseStatements.scala:26)
at akka.japi.pf.UnitCaseStatement.apply(CaseStatements.scala:21)
at scala.PartialFunction.applyOrElse(PartialFunction.scala:123)
at scala.PartialFunction.applyOrElse$(PartialFunction.scala:122)
at akka.japi.pf.UnitCaseStatement.applyOrElse(CaseStatements.scala:21)
at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:171)
at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:172)
at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:172)
at akka.actor.Actor.aroundReceive(Actor.scala:517)
at akka.actor.Actor.aroundReceive$(Actor.scala:515)
at akka.actor.AbstractActor.aroundReceive(AbstractActor.scala:225)
at akka.actor.ActorCell.receiveMessage(ActorCell.scala:592)
at akka.actor.ActorCell.invoke(ActorCell.scala:561)
at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:258)
at akka.dispatch.Mailbox.run(Mailbox.scala:225)
at akka.dispatch.Mailbox.exec(Mailbox.scala:235)
at akka.dispatch.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260)
at akka.dispatch.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339)
at akka.dispatch.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979)
at akka.dispatch.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107)
Caused by: java.lang.RuntimeException: Could not extract key from {"device":"rand-numeric","id":"b4728895-741f-466a-b87b-79c7590893b4","origin":"1591095418904441036","readings":[{"origin":"1591095418904328442","valueType":"Int64","name":"int","device":"rand-numeric","value":"0"}]}
at org.apache.flink.streaming.runtime.io.RecordWriterOutput.pushToRecordWriter(RecordWriterOutput.java:110)
at org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:89)
at org.apache.flink.streaming.runtime.io.RecordWriterOutput.collect(RecordWriterOutput.java:45)
at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:730)
at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:708)
at org.apache.flink.streaming.api.operators.StreamSourceContexts$NonTimestampContext.collect(StreamSourceContexts.java:104)
at io.pravega.connectors.flink.FlinkPravegaReader.run(FlinkPravegaReader.java:307)
at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:100)
at org.apache.flink.streaming.api.operators.StreamSource.run(StreamSource.java:63)
at org.apache.flink.streaming.runtime.tasks.SourceStreamTask$LegacySourceFunctionThread.run(SourceStreamTask.java:200)
Caused by: java.lang.RuntimeException: Could not extract key from {"device":"rand-numeric","id":"b4728895-741f-466a-b87b-79c7590893b4","origin":"1591095418904441036","readings":[{"origin":"1591095418904328442","valueType":"Int64","name":"int","device":"rand-numeric","value":"0"}]}
at org.apache.flink.streaming.runtime.partitioner.KeyGroupStreamPartitioner.selectChannel(KeyGroupStreamPartitioner.java:56)
at org.apache.flink.streaming.runtime.partitioner.KeyGroupStreamPartitioner.selectChannel(KeyGroupStreamPartitioner.java:32)
at org.apache.flink.runtime.io.network.api.writer.ChannelSelectorRecordWriter.emit(ChannelSelectorRecordWriter.java:60)
at org.apache.flink.streaming.runtime.io.RecordWriterOutput.pushToRecordWriter(RecordWriterOutput.java:107)
... 9 more
Caused by: java.lang.ClassCastException: java.lang.String cannot be cast to org.apache.flink.shaded.jackson2.com.fasterxml.jackson.databind.node.ObjectNode
at myflink.StreamingJob$1.getKey(StreamingJob.java:125)
at org.apache.flink.streaming.runtime.partitioner.KeyGroupStreamPartitioner.selectChannel(KeyGroupStreamPartitioner.java:54)
... 12 more

Answer 1

You can check the rules for POJO types here.
Rules for POJO types
By using POJO types, Flink can infer a lot of information about the data types that are exchanged and stored during the distributed computation.
The following codes define POJOs for you input.
public class FlinkPOJO {
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
env.setParallelism(3);
DataStream<String> source =
env.addSource(new SourceFunction<String>() {
#Override
public void run(SourceContext<String> sourceContext) throws Exception {
while (true) {
sourceContext.collect("{\"device\":\"rand-numeric\",\"id\":\"b4728895-741f-466a-b87b-79c7590893b4\",\"origin\":\"1591095418904441036\",\"readings\":[{\"origin\":\"1591095418904328442\",\"valueType\":\"Int64\",\"name\":\"int\",\"device\":\"rand-numeric\",\"value\":\"0\"}]}");
Thread.sleep(1000);
}
}
#Override
public void cancel() {
}
});
DataStream<Info> parsedSource =
source.map(new MapFunction<String, Info>() {
#Override
public Info map(String s) throws Exception {
Gson gson = new Gson();
return gson.fromJson(s, Info.class);
}
});
DataStream<String> output = parsedSource.keyBy(Info::getId).timeWindow(Time.seconds(1))
.process(new ProcessWindowFunction<Info, String, String, TimeWindow>() {
#Override
public void process(String s, Context context, Iterable<Info> iterable, Collector<String> collector) throws Exception {
int count = 0;
Iterator<Info> iterator = iterable.iterator();
while (iterator.hasNext()) {
count++;
iterator.next();
}
collector.collect(String.format("key : %s, size : %s", s, count));
}
});
output.print();
env.execute();
}
public class Info {
public String getDevice() {
return device;
}
public void setDevice(String device) {
this.device = device;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getOrigin() {
return origin;
}
public void setOrigin(String origin) {
this.origin = origin;
}
public Reading[] getReadings() {
return readings;
}
public void setReadings(Reading[] readings) {
this.readings = readings;
}
public String device;
public String id;
public String origin;
public Reading[] readings;
public Info() {
}
}
public class Reading {
public String origin;
public String valueType;
public String name;
public String device;
public String value;
public Reading() {
}
}
}
Actually, you can define a brief POJO which only contains the fields you need.