本文介绍了Apache Flink:由TupleSerializer引起的NullPointerException的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
当我执行Flink应用程序时，它会给我这个NullPointerException:
When I execute my Flink application it gives me this NullPointerException:
2017-08-08 13:21:57,690 INFO com.datastax.driver.core.Cluster - New Cassandra host /127.0.0.1:9042 added
2017-08-08 13:22:02,427 INFO org.apache.flink.runtime.taskmanager.Task - TriggerWindow(TumblingEventTimeWindows(30000), ListStateDescriptor{serializer=org.apache.flink.api.common.typeutils.base.ListSerializer@15d1c80b}, EventTimeTrigger(), WindowedStream.apply(CoGroupedStreams.java:302)) -> Filter -> Flat Map -> Sink: Cassandra Sink (1/1) (092a7ef50209f7a050d9d82be1e03d80) switched from RUNNING to FAILED.
java.lang.RuntimeException: Exception occurred while processing valve output watermark:
at org.apache.flink.streaming.runtime.io.StreamInputProcessor$ForwardingValveOutputHandler.handleWatermark(StreamInputProcessor.java:289)
at org.apache.flink.streaming.runtime.streamstatus.StatusWatermarkValve.findAndOutputNewMinWatermarkAcrossAlignedChannels(StatusWatermarkValve.java:173)
at org.apache.flink.streaming.runtime.streamstatus.StatusWatermarkValve.inputWatermark(StatusWatermarkValve.java:108)
at org.apache.flink.streaming.runtime.io.StreamInputProcessor.processInput(StreamInputProcessor.java:188)
at org.apache.flink.streaming.runtime.tasks.OneInputStreamTask.run(OneInputStreamTask.java:69)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:263)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:702)
at java.lang.Thread.run(Thread.java:748)
Caused by: org.apache.flink.streaming.runtime.tasks.ExceptionInChainedOperatorException: Could not forward element to next operator
at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:530)
at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:503)
at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.collect(OperatorChain.java:483)
at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:891)
at org.apache.flink.streaming.api.operators.AbstractStreamOperator$CountingOutput.collect(AbstractStreamOperator.java:869)
at org.apache.flink.streaming.api.operators.TimestampedCollector.collect(TimestampedCollector.java:51)
at org.apache.flink.streaming.api.datastream.JoinedStreams$JoinCoGroupFunction.coGroup(JoinedStreams.java:400)
at org.apache.flink.streaming.api.datastream.CoGroupedStreams$CoGroupWindowFunction.apply(CoGroupedStreams.java:682)
at org.apache.flink.streaming.runtime.operators.windowing.functions.InternalIterableWindowFunction.process(InternalIterableWindowFunction.java:43)
at org.apache.flink.streaming.runtime.operators.windowing.functions.InternalIterableWindowFunction.process(InternalIterableWindowFunction.java:31)
at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator.emitWindowContents(WindowOperator.java:597)
at org.apache.flink.streaming.runtime.operators.windowing.WindowOperator.onEventTime(WindowOperator.java:504)
at org.apache.flink.streaming.api.operators.HeapInternalTimerService.advanceWatermark(HeapInternalTimerService.java:275)
at org.apache.flink.streaming.api.operators.InternalTimeServiceManager.advanceWatermark(InternalTimeServiceManager.java:107)
at org.apache.flink.streaming.api.operators.AbstractStreamOperator.processWatermark(AbstractStreamOperator.java:946)
at org.apache.flink.streaming.runtime.io.StreamInputProcessor$ForwardingValveOutputHandler.handleWatermark(StreamInputProcessor.java:286)
... 7 more
Caused by: java.lang.NullPointerException
at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.copy(TupleSerializer.java:104)
at org.apache.flink.api.java.typeutils.runtime.TupleSerializer.copy(TupleSerializer.java:30)
at org.apache.flink.streaming.runtime.tasks.OperatorChain$CopyingChainingOutput.pushToOperator(OperatorChain.java:526)
... 22 more
推荐答案
Flink的元组序列化器不支持空值.您应该检查元组是否包含空字段.
Flink's tuple serializers do not support null values. You should check if a Tuple contains a null field.
元组的替代方法是POJO或Row类型. Row支持任意许多可为空的字段，但需要明确的类型说明.
An alternative to tuples are POJOs or the Row type. Row supports arbitrary many nullable fields but requires explicit type specification.
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