初始化 Sate 会导致此错误"java.lang.NullPointerException: Keyed state can only be used on a 'keyed stream'"

Question

我正在尝试在CoProcessFunction中初始化"ListState"，但是它不断抛出此错误 "java.lang.NullPointerException：keyed state只能用于'keyed stream'"。

这是我使用的代码 Sinnpet

dataStream1.keyBy(ele->ele.f1).connect(dataStream2).process(
new CoProcessFunction<Tuple2<Long, String>, String, Object>() {
ListState stream1ListState;

@Override
public void open(Configuration parameters) throws Exception {
LOG.info("inside CoProcess Function Constructor");
ListStateDescriptor<Tuple2<Long,String>> listStateDescriptor = new
ListStateDescriptor<Tuple2<Long,String>>("type1",TypeInformation.of(new TypeHint<Tuple2<Long,String>>(){}));
stream1ListState = getRuntimeContext().getListState(listStateDescriptor);
}

@Override
public void processElement1(Tuple2<Long, String> longStringTuple2, Context context,
Collector<Object> collector) throws Exception {
LOG.info("inside stream1 processor");
LOG.info(longStringTuple2.toString());
collector.collect(longStringTuple2);
}

@Override
public void processElement2(String s, Context context, Collector<Object> collector)
throws Exception {
LOG.info("inside stream2 processor");
LOG.info(s);
}
}).print();

引发此错误的行是该行

stream1ListState = getRuntimeContext().getListState(listStateDescriptor);

其余的错误日志跟踪如下

Caused by: java.lang.NullPointerException: Keyed state can only be used on a 'keyed stream', i.e., after a 'keyBy()' operation.
at org.apache.flink.util.Preconditions.checkNotNull(Preconditions.java:76)
at org.apache.flink.streaming.api.operators.StreamingRuntimeContext.checkPreconditionsAndGetKeyedStateStore(StreamingRuntimeContext.java:232)
at org.apache.flink.streaming.api.operators.StreamingRuntimeContext.getListState(StreamingRuntimeContext.java:202)

Answer 1

该错误意味着您只能在KeyedCoProcessFunction内部使用ListState、ValueState等，而这反过来只能在两个流都键控时使用。因此，如果第二个流是正常流，并且可以通过某个键进行键控，那么您可以这样做，否则您可能需要参考此处所述的广播状态模式。