堆栈内存溢出
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Flux.generate() 正在抛出 java.lang.IllegalStateException：生成器没有调用任何 SynchronousSink 方法

[英]Flux.generate() is throwing java.lang.IllegalStateException: The generator didn't call any of the SynchronousSink method

 原文  2020-12-19 20:17:16  6   1    java/ spring-boot/ reactive-programming/ spring-webflux

问题描述

I am trying to do my first steps in reactive programming with Spring Boot (2.3.4.RELEASE).我正在尝试使用 Spring Boot (2.3.4.RELEASE) 进行反应式编程的第一步。 So far I am trying to creating an infinte stream of persons in a service method which is called in a REST controller method but it ends with that exception: "java.lang.IllegalStateException: The generator didn't call any of the SynchronousSink method " I tried to google some solutions for a few hours but I haven't found any propper one which fits to what I am trying to do. So far I am trying to creating an infinte stream of persons in a service method which is called in a REST controller method but it ends with that exception: "java.lang.IllegalStateException: The generator didn't call any of the SynchronousSink method "我试图用谷歌搜索一些解决方案几个小时，但我没有找到任何适合我想要做的事情的合适的解决方案。

This is my service method:这是我的服务方法：

public Flux<PersonEntity> streamPersons() {
        return personRepository.findMinId()
                .zipWith(personRepository.findMaxId())
                .flatMapMany(minMaxTuple ->
                        Flux.<PersonEntity> generate(stream ->
                                personRepository.findById(new Random().longs(minMaxTuple.getT1(), minMaxTuple.getT2()).findFirst().getAsLong()
                                )
                        ).delayElements(Duration.ofMillis(300))
                );
    }

UPDATE 1更新 1

I tried this code snippet from the latest update in the below answer.我从以下答案的最新更新中尝试了此代码片段。 Method is looking like that now:方法现在看起来像这样：

    public Flux<PersonEntity> streamPersons() {
        return personRepository.findMinId()
                .zipWith(personRepository.findMaxId())
                .flatMapMany(minMaxTuple ->
                        Flux.<PersonEntity>generate(sink -> {
                            Mono<PersonEntity> foundStock = stockRepository.findById(new Random().longs(minMaxTuple.getT1(), minMaxTuple.getT2()).findFirst().getAsLong());
                            sink.next(foundStock);
                        }
                        ).delayElements(Duration.ofMillis(300))
                );
    }

Unfortunately I am getting a compiler error and I don't know how to get rid of it.不幸的是，我遇到了编译器错误，我不知道如何摆脱它。 The local variable foundStock is a Mono, but the method sink.next(...) requires a regular PersonEntity.局部变量 foundStock 是一个 Mono，但是方法 sink.next(...) 需要一个常规的 PersonEntity。 How to convert this without blocking?如何在不阻塞的情况下转换它？

Update 2更新 2

This solution is the one, which works for me.这个解决方案就是对我有用的解决方案。 My intention is to get a random person from the database to stream it in an infinte stream to the requesting instance.我的意图是从数据库中随机获取一个人到 stream 它在一个无限的 stream 到请求实例。 Special thanks goes to @Toerktumlare !特别感谢@Toerktumlare！

public Flux<PersonEntity> streamPersons() {
    Mono<Tuple2<Long, Long>> minMaxIdTuple = personRepository.findMinId()
            .zipWith(personRepository.findMaxId());
    Flux<Long> interval = Flux.interval(Duration.ofSeconds(1));
    
    return interval.flatMapSequential(aLong ->
           minMaxIdTuple.map(minMaxTuple ->
                new Random().longs(minMaxTuple.getT1(), minMaxTuple.getT2()))
                    .flatMapMany(longStream -> personRepository.findById(
                         longStream.findFirst().getAsLong()))
                    .flatMap(Flux::just)
        );
    }

My controller method is looking like that:我的 controller 方法如下所示：

    @GetMapping(value = "/person/stream", produces = MediaType.TEXT_EVENT_STREAM_VALUE)
    public Flux<PersonEntity> streamPersons() {
        return personService.streamPersons();
    }

The full stacktrace of the above mentioned exception上述异常的完整堆栈跟踪

java.lang.IllegalStateException: The generator didn't call any of the SynchronousSink method
    at reactor.core.publisher.FluxGenerate$GenerateSubscription.slowPath(FluxGenerate.java:276) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
    Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
    |_ checkpoint ⇢ Handler first.reactive.steps.controller.provider.PersonController#streamPersons() [DispatcherHandler]
    |_ checkpoint ⇢ HTTP GET "/personapp/api/v1/persons/stream" [ExceptionHandlingWebHandler]
Stack trace:
        at reactor.core.publisher.FluxGenerate$GenerateSubscription.slowPath(FluxGenerate.java:276) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxGenerate$GenerateSubscription.request(FluxGenerate.java:204) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoFlatMapMany$FlatMapManyMain.onSubscribeInner(MonoFlatMapMany.java:143) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoFlatMapMany$FlatMapManyInner.onSubscribe(MonoFlatMapMany.java:237) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxGenerate.subscribe(FluxGenerate.java:83) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Flux.subscribe(Flux.java:8325) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoFlatMapMany$FlatMapManyMain.onNext(MonoFlatMapMany.java:188) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1782) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoZip$ZipCoordinator.signal(MonoZip.java:247) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoZip$ZipInner.onNext(MonoZip.java:329) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:76) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.tryEmitScalar(FluxFlatMap.java:480) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.onNext(FluxFlatMap.java:413) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxBuffer$BufferExactSubscriber.onComplete(FluxBuffer.java:179) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:2016) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxUsingWhen$UsingWhenSubscriber.deferredComplete(FluxUsingWhen.java:402) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxUsingWhen$CommitInner.onComplete(FluxUsingWhen.java:536) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:2016) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxPeek$PeekSubscriber.onComplete(FluxPeek.java:252) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onComplete(Operators.java:2016) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$MonoSubscriber.onComplete(Operators.java:1824) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen$ThenAcceptInner.onComplete(MonoIgnoreThen.java:314) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$MonoSubscriber.onComplete(Operators.java:1824) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen$ThenAcceptInner.onComplete(MonoIgnoreThen.java:314) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.pool.SimpleDequePool$QueuePoolRecyclerInner.onComplete(SimpleDequePool.java:555) ~[reactor-pool-0.1.6.RELEASE.jar:0.1.6.RELEASE]
        at reactor.core.publisher.Operators.complete(Operators.java:135) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:45) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.pool.SimpleDequePool$QueuePoolRecyclerMono.subscribe(SimpleDequePool.java:667) ~[reactor-pool-0.1.6.RELEASE.jar:0.1.6.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:153) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:153) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:97) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onError(MonoIgnoreElements.java:76) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onError(FluxMapFuseable.java:134) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableSubscriber.onError(FluxFilterFuseable.java:156) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onError(FluxFilterFuseable.java:375) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onError(FluxMapFuseable.java:326) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onNext(FluxHandleFuseable.java:185) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2344) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.request(FluxHandleFuseable.java:243) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.request(FluxMapFuseable.java:346) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.request(FluxFilterFuseable.java:403) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableSubscriber.request(FluxFilterFuseable.java:184) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:162) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoIgnoreElements$IgnoreElementsSubscriber.onSubscribe(MonoIgnoreElements.java:64) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableSubscriber.onSubscribe(FluxFilterFuseable.java:81) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFilterFuseable$FilterFuseableConditionalSubscriber.onSubscribe(FluxFilterFuseable.java:298) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableConditionalSubscriber.onSubscribe(FluxMapFuseable.java:255) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxHandleFuseable$HandleFuseableSubscriber.onSubscribe(FluxHandleFuseable.java:148) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoCurrentContext.subscribe(MonoCurrentContext.java:35) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.Mono.subscribe(Mono.java:4213) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxUsingWhen$UsingWhenSubscriber.onComplete(FluxUsingWhen.java:394) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.checkTerminated(FluxFlatMap.java:838) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.drainLoop(FluxFlatMap.java:600) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.drain(FluxFlatMap.java:580) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxFlatMap$FlatMapMain.onComplete(FluxFlatMap.java:457) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMap$MapSubscriber.onComplete(FluxMap.java:136) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxContextStart$ContextStartSubscriber.onComplete(FluxContextStart.java:115) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at io.r2dbc.postgresql.util.FluxDiscardOnCancel$FluxDiscardOnCancelSubscriber.onComplete(FluxDiscardOnCancel.java:99) ~[r2dbc-postgresql-0.8.5.RELEASE.jar:0.8.5.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onComplete(FluxMapFuseable.java:144) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onComplete(FluxMapFuseable.java:144) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxWindowPredicate$WindowPredicateMain.checkTerminated(FluxWindowPredicate.java:520) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxWindowPredicate$WindowPredicateMain.drainLoop(FluxWindowPredicate.java:468) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxWindowPredicate$WindowPredicateMain.drain(FluxWindowPredicate.java:412) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxWindowPredicate$WindowPredicateMain.onComplete(FluxWindowPredicate.java:293) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxCreate$BaseSink.complete(FluxCreate.java:438) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxCreate$BufferAsyncSink.drain(FluxCreate.java:784) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxCreate$BufferAsyncSink.complete(FluxCreate.java:732) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxCreate$SerializedSink.drainLoop(FluxCreate.java:239) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxCreate$SerializedSink.drain(FluxCreate.java:205) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxCreate$SerializedSink.complete(FluxCreate.java:196) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at io.r2dbc.postgresql.client.ReactorNettyClient$Conversation.complete(ReactorNettyClient.java:709) ~[r2dbc-postgresql-0.8.5.RELEASE.jar:0.8.5.RELEASE]
        at io.r2dbc.postgresql.client.ReactorNettyClient$BackendMessageSubscriber.emit(ReactorNettyClient.java:974) ~[r2dbc-postgresql-0.8.5.RELEASE.jar:0.8.5.RELEASE]
        at io.r2dbc.postgresql.client.ReactorNettyClient$BackendMessageSubscriber.onNext(ReactorNettyClient.java:850) ~[r2dbc-postgresql-0.8.5.RELEASE.jar:0.8.5.RELEASE]
        at io.r2dbc.postgresql.client.ReactorNettyClient$BackendMessageSubscriber.onNext(ReactorNettyClient.java:757) ~[r2dbc-postgresql-0.8.5.RELEASE.jar:0.8.5.RELEASE]
        at reactor.core.publisher.FluxHandle$HandleSubscriber.onNext(FluxHandle.java:112) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxPeekFuseable$PeekConditionalSubscriber.onNext(FluxPeekFuseable.java:845) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:213) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.core.publisher.FluxMap$MapConditionalSubscriber.onNext(FluxMap.java:213) ~[reactor-core-3.3.10.RELEASE.jar:3.3.10.RELEASE]
        at reactor.netty.channel.FluxReceive.drainReceiver(FluxReceive.java:256) ~[reactor-netty-0.9.12.RELEASE.jar:0.9.12.RELEASE]
        at reactor.netty.channel.FluxReceive.onInboundNext(FluxReceive.java:362) ~[reactor-netty-0.9.12.RELEASE.jar:0.9.12.RELEASE]
        at reactor.netty.channel.ChannelOperations.onInboundNext(ChannelOperations.java:358) ~[reactor-netty-0.9.12.RELEASE.jar:0.9.12.RELEASE]
        at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:96) ~[reactor-netty-0.9.12.RELEASE.jar:0.9.12.RELEASE]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:324) ~[netty-codec-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:296) ~[netty-codec-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:714) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:650) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:576) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:493) ~[netty-transport-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:989) ~[netty-common-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.52.Final.jar:4.1.52.Final]
        at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.52.Final.jar:4.1.52.Final]
        at java.base/java.lang.Thread.run(Thread.java:834) ~[na:na]

Any help or hint is highly appreciated.非常感谢任何帮助或提示。 Thanks in advance提前致谢

1 个解决方案

解决方案1
 2 已采纳  2020-12-19 23:41:03

A Mono or a Flux contain something called a sink . Mono或Flux包含称为sink的东西。 The generator function, is the simplest form of generating a steady stream of items.生成器 function 是生成稳定的 stream 项目的最简单形式。 The default sink is synchronous and used for one-by-one emissions, hence synchronousSink .默认接收器是synchronous的，用于one-by-one发射，因此是synchronousSink 。

So by calling the generator method you expose the inner sink, and you need to feed items through the sink api by calling the sinks functions next , complete or error function.因此，通过调用生成器方法，您可以公开内部接收器，并且您需要通过调用接收器函数next 、 complete或error function 来通过接收器 api 提供项目。

Example:例子：

Flux<String> flux = Flux.generate(
    () -> 0, 
    (state, sink) -> {
      sink.next("3 x " + state + " = " + 3*state); 
      if (state == 10) sink.complete(); 
      return state + 1; 
    });

Here we are using the function signature:这里我们使用 function 签名：

Flux#generate(Callable<S> stateSupplier, BiFunction<S,SynchronousSink<T>,S> generator)

So we are:所以我们是：

  • We supply the initial state value of 0.我们提供的初始 state 值为 0。
  • We use the state to choose what to emit (a row in the multiplication table of 3).我们使用 state 来选择发射什么（乘法表中的 3 行）。
  • We also use it to choose when to stop.我们还使用它来选择何时停止。
  • We return a new state that we use in the next invocation (unless the sequence terminated in this one).我们返回一个新的 state，我们将在下一次调用中使用它（除非序列在这个调用中终止）。

This starts off as soon as we subscribe to the flux.一旦我们订阅了通量，这就会开始。

The above code will generate the following sequence.上面的代码将生成以下序列。

3 x 0 = 0
3 x 1 = 3
3 x 2 = 6
3 x 3 = 9
3 x 4 = 12
3 x 5 = 15
3 x 6 = 18
3 x 7 = 21
3 x 8 = 24
3 x 9 = 27
3 x 10 = 30

In your code you are not calling the sinks next method in the generate function.在您的代码中，您没有在生成 function 中调用 sinks next 方法。

You can read more about how sinks and the generator function works in the official Reactor Documentation - Producing These docs should be your first source before googling anything else.您可以在官方Reactor 文档中阅读更多关于接收器和生成器 function 的工作原理 - 生产这些文档应该是您在谷歌搜索其他任何内容之前的第一个来源。

UPDATE:更新：

After this answer was posted this comment was posted:发布此答案后，发布了此评论：

"why does this example work and not my code" “为什么这个例子有效，而不是我的代码”

The example he is referring to is:他所指的例子是：

Flux<Dish> getDishes() {
    return Flux.<Dish> generate(sink -> sink.next(randomDish())) //
                .delayElements(Duration.ofMillis(250));
}

Here we can clearly see that he is using the internal sink and calling sink#next each time to send a random dish out to the subscribing client.在这里我们可以清楚地看到他正在使用内部接收sink ，并且每次调用sink#next向订阅客户端发送一个随机菜。

While in the code provided by the thread starter:在线程启动器提供的代码中：

Flux.<PersonEntity> generate(stream ->
       personRepository.findById(new Random()
           .longs(minMaxTuple.getT1(), minMaxTuple.getT2())
           .findFirst()
           .getAsLong()))
       .delayElements(Duration.ofMillis(300))

No sink is being used.没有使用水槽。

Generator methods is for generating items, which means that the sink needs a concrete object.生成器方法用于生成项目，这意味着接收器需要具体的 object。 It cannot be a Mono or a Flux .它不能是Mono或Flux 。 If you need to return such, you convert between them and return them straight to the client.如果您需要返回这些，您可以在它们之间进行转换并将它们直接返回给客户。

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