json - Apache Flink:无法从 ObjectNode::get 中提取 key

Question

我正在使用 Flink 处理来自某些数据源(例如 Kafka、Pravega 等)的数据。

就我而言，数据源是 Pravega，它为我提供了一个 flink 连接器。

我的数据源正在向我发送一些 JSON 数据，如下所示:

{"device":"rand-numeric","id":"b4728895-741f-466a-b87b-79c7590893b4","origin":"1591095418904441036","readings":[{"origin":"1591095418904328442","valueType":"Int64","name":"int","device":"rand-numeric","value":"0"}]}

这是我的代码:

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");

如您所见，我使用了 FlinkPravegaReader 和适当的反序列化器来获取来自 Pravega 的 JSON 流。

然后我尝试使用自定义 KeySelector 对其进行 KeyBy 并打印它。

但是，我收到错误:

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"}]}

似乎 node.get("id").asText(); 抛出了这个异常。

我不知道为什么。正如我们所见，JSON 数据中确实存在一个名为 id 的键。为什么提取不出来呢？我是否错误地使用了 ObjectNode 类或其他原因？

堆栈跟踪:

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

您可以在此处查看 POJO 类型的规则。

Rules for POJO types

通过使用 POJO 类型，Flink 可以推断出分布式计算过程中交换和存储的数据类型的大量信息。

以下代码为您的输入定义 POJO。

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() {

        }
    }
}

实际上，您可以定义一个简短的 POJO，其中只包含您需要的字段。