我正在尝试在 Flink 中的 KeyedStream 上执行映射操作:
stream.map(new JsonToMessageObjectMapper())
.keyBy("keyfield")
.map(new MessageProcessorStateful())
JsonToObjectMapper 运算符的输出是类的 POJO消息对象其中有一个字符串字段 'keyfield'。然后将流键入该字段。
MessageProcessorStateful 是一个 RichMapFunction,如下所示:
public class MessageAdProcessorStateful extends RichMapFunction<MessageObject, Tuple2<String, String>> {
private transient MapState<String, Tuple2<Tuple3<String, String, String>, Tuple2<Double, Long>>> state;
...
@Override
public void open(Configuration config) throws Exception {
MapStateDescriptor<String, Tuple2<Tuple3<String, String, String>, Tuple2<Double, Long>>> descriptor =
new MapStateDescriptor<>(
"state", // the state name
TypeInformation.of(new TypeHint<String>() {}),
TypeInformation.of(new TypeHint<Tuple2<Tuple3<String, String, String>, Tuple2<Double, Long>>>() {}) ); // type information
state = getRuntimeContext().getMapState(descriptor);
state.put(...); // Insert a key, value here. Exception here!
}
}
代码抛出 NullPointer 异常:
Caused by: java.lang.NullPointerException: No key set. This method should not be called outside of a keyed context.
at org.apache.flink.util.Preconditions.checkNotNull(Preconditions.java:75)
at org.apache.flink.runtime.state.heap.CopyOnWriteStateTable.checkKeyNamespacePreconditions(CopyOnWriteStateTable.java:528)
at org.apache.flink.runtime.state.heap.CopyOnWriteStateTable.computeHashForOperationAndDoIncrementalRehash(CopyOnWriteStateTable.java:722)
at org.apache.flink.runtime.state.heap.CopyOnWriteStateTable.get(CopyOnWriteStateTable.java:265)
at org.apache.flink.runtime.state.heap.CopyOnWriteStateTable.get(CopyOnWriteStateTable.java:306)
at org.apache.flink.runtime.state.heap.HeapMapState.put(HeapMapState.java:75)
at org.apache.flink.runtime.state.UserFacingMapState.put(UserFacingMapState.java:52)
at org.myorg.quickstart.MessageStreamProcessor$MessageAdProcessorStateful.open(MessageStreamProcessor.java:226)
at org.apache.flink.api.common.functions.util.FunctionUtils.openFunction(FunctionUtils.java:36)
at org.apache.flink.streaming.api.operators.AbstractUdfStreamOperator.open(AbstractUdfStreamOperator.java:102)
at org.apache.flink.streaming.runtime.tasks.StreamTask.openAllOperators(StreamTask.java:393)
at org.apache.flink.streaming.runtime.tasks.StreamTask.invoke(StreamTask.java:254)
at org.apache.flink.runtime.taskmanager.Task.run(Task.java:718)
at java.lang.Thread.run(Thread.java:748)
尽管我已验证“keyfield”始终是有效字符串,但 KeyedStream 之一的 keyedState 中的键似乎为 null。根据 Flink 文档,其余似乎是正确的。知道发生了什么事吗?