Spring WebFlux：只允许一个连接接收订阅者

Z时代
2024-01-10
分类：问答

我正在用Spring 5 Webflux和Kotlin编写一个简单的应用程序。我正在尝试通过以下方式实现PUT端点：

PUT("/confs/{id}", {
    val id = it.pathVariable("id")
    ServerResponse.ok().body(service.save(it.bodyToMono(Item::class.java)), Item::class.java)
})

保存的诀窍是，我尝试从项目中读取城市名称，解析地理坐标，将其覆盖在原始项目中，然后使用Spring Data Mongo Reactive

repo保存到Mongo。

fun save(item: Mono<Item>): Mono<Item> {
    val geo = item.flatMap {
            val city = it.location?.city ?: "Somewhere"
            geoService.resolveGeoFromCity(city)
    }
    val zipped = item.zipWith(geo)
        .map {
            it.t1.location?.geo = it.t2
            it.t1
        }
    return repo.saveAll(zipped)
        .toMono()
}

解析地理坐标的代码在这里：

@Service
class GeoService() {
    val client = WebClient.create("https://maps.googleapis.com/maps/api/geocode/")
    fun resolveGeoFromCity(city: String): Mono<Geo> {
        return client.get()
                .uri("json?address=$city&key=$API_KEY&language=en")
                .exchange()
                .flatMap { it.bodyToMono(String::class.java) }
                .map { parse(it) }
    }
    private fun parse(response: String): Geo {
        val locationMap = JsonPath.read<Map<String, Double>>(response, "$.results[0].geometry.location")
        return Geo(locationMap["lat"] ?: 0.0, locationMap["lng"] ?: 0.0)
    }
}

问题是，如果发出PUT请求，我将遵循stacktrace。我试图用val geo = Mono.just(Geo(0.0,

0.0))（不使用WebClient）对Mono进行存根处理，然后工作正常。

如何在不牺牲功能的情况下进行修复？）

    2018-01-01 01:41:00.595 ERROR 15120 --- [ctor-http-nio-4] .a.w.r.e.DefaultErrorWebExceptionHandler : Failed to handle request [PUT http://localhost:8097/confs/5a49675c910d123b1057207a]
    java.lang.IllegalStateException: Only one connection receive subscriber allowed.
        at reactor.ipc.netty.channel.FluxReceive.startReceiver(FluxReceive.java:276) ~[reactor-netty-0.7.2.RELEASE.jar:0.7.2.RELEASE]
        at reactor.ipc.netty.channel.FluxReceive.subscribe(FluxReceive.java:124) ~[reactor-netty-0.7.2.RELEASE.jar:0.7.2.RELEASE]
        at reactor.core.publisher.FluxMap.subscribe(FluxMap.java:62) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxOnAssembly.subscribe(FluxOnAssembly.java:252) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.ipc.netty.ByteBufFlux.subscribe(ByteBufFlux.java:242) ~[reactor-netty-0.7.2.RELEASE.jar:0.7.2.RELEASE]
        at reactor.core.publisher.FluxPeek.subscribe(FluxPeek.java:83) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxOnAssembly.subscribe(FluxOnAssembly.java:252) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.ipc.netty.ByteBufFlux.subscribe(ByteBufFlux.java:242) ~[reactor-netty-0.7.2.RELEASE.jar:0.7.2.RELEASE]
        at reactor.core.publisher.FluxMap.subscribe(FluxMap.java:62) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxOnAssembly.subscribe(FluxOnAssembly.java:252) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxFlatMap.subscribe(FluxFlatMap.java:97) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxOnAssembly.subscribe(FluxOnAssembly.java:252) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxDoFinallyFuseable.subscribe(FluxDoFinallyFuseable.java:48) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxOnAssembly.subscribe(FluxOnAssembly.java:252) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxMapFuseable.subscribe(FluxMapFuseable.java:63) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.FluxOnAssembly.subscribe(FluxOnAssembly.java:252) ~
[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:74) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.Mono.subscribe(Mono.java:3008) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:167) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:71) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.core.publisher.MonoOnAssembly.subscribe(MonoOnAssembly.java:76) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
        at reactor.ipc.netty.channel.ChannelOperations.applyHandler(ChannelOperations.java:383) ~[reactor-netty-0.7.2.RELEASE.jar:0.7.2.RELEASE]
        at reactor.ipc.netty.http.server.HttpServerOperations.onHandlerStart(HttpServerOperations.java:359) ~[reactor-netty-0.7.2.RELEASE.jar:0.7.2.RELEASE]
        at io.netty.util.concurrent.AbstractEventExecutor.safeExecute$$$capture(AbstractEventExecutor.java:163) ~[netty-common-4.1.17.Final.jar:4.1.17.Final]
        at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java) ~[netty-common-4.1.17.Final.jar:4.1.17.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403) ~[netty-common-4.1.17.Final.jar:4.1.17.Final]
        at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463) ~[netty-transport-4.1.17.Final.jar:4.1.17.Final]
        at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858) ~[netty-common-4.1.17.Final.jar:4.1.17.Final]
        at java.lang.Thread.run(Thread.java:745) ~[na:1.8.0_112]
        Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
    Assembly trace from producer [reactor.core.publisher.FluxMap] :
        reactor.core.publisher.Flux.map(Flux.java:4855)
        reactor.ipc.netty.ByteBufFlux.fromInbound(ByteBufFlux.java:68)
        reactor.ipc.netty.NettyInbound.receive(NettyInbound.java:90)
        org.springframework.http.server.reactive.ReactorServerHttpRequest.getBody(ReactorServerHttpRequest.java:148)
        org.springframework.http.codec.DecoderHttpMessageReader.readMono(DecoderHttpMessageReader.java:93)
        org.springframework.http.codec.DecoderHttpMessageReader.readMono(DecoderHttpMessageReader.java:123)
        org.springframework.web.reactive.function.BodyExtractors.lambda$null$0(BodyExtractors.java:101)
        java.util.Optional.map(Optional.java:215)
        org.springframework.web.reactive.function.BodyExtractors.readWithMessageReaders(BodyExtractors.java:256)
        org.springframework.web.reactive.function.BodyExtractors.lambda$toMono$2(BodyExtractors.java:96)
        org.springframework.web.reactive.function.server.DefaultServerRequest.body(DefaultServerRequest.java:126)
        org.springframework.web.reactive.function.server.DefaultServerRequest.body(DefaultServerRequest.java:120)
        org.springframework.web.reactive.function.server.DefaultServerRequest.bodyToMono(DefaultServerRequest.java:145)
        com.example.confs.web.ConferenceRouter$routes$1$2.invoke(ConferenceRouter.kt:31)
        com.example.confs.web.ConferenceRouter$routes$1$2.invoke(ConferenceRouter.kt:16)
        org.springframework.web.reactive.function.server.RouterFunctionDsl$PUT$1.handle(RouterFunctionDsl.kt:200)
        org.springframework.web.reactive.function.server.support.HandlerFunctionAdapter.handle(HandlerFunctionAdapter.java:61)
        org.springframework.web.reactive.DispatcherHandler.invokeHandler(DispatcherHandler.java:168)
        org.springframework.web.reactive.DispatcherHandler.lambda$handle$1(DispatcherHandler.java:160)
        reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:118)
        reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
        reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:76)
        reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:271)
        reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:803)
        reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:115)
        reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
        reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
        reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
        reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
        reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:1649)
        reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:1463)
        reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:1337)
        reactor.core.publisher.MonoJust.subscribe(MonoJust.java:54)
        reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
        reactor.core.publisher.Mono.subscribe(Mono.java:3008)
        reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onComplete(FluxSwitchIfEmpty.java:75)
        reactor.core.publisher.Operators.complete(Operators.java:125)
        reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:45)
        reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44)
        reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44)
        reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44)
        reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44)
        reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
        reactor.core.publisher.Mono.subscribe(Mono.java:3008)
        reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:418)
        reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:210)
        reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:128)
        reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:61)
        reactor.core.publisher.FluxConcatMap.subscribe(FluxConcatMap.java:121)
        reactor.core.publisher.MonoNext.subscribe(MonoNext.java:40)
        reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44)
        reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60)
        reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60)
        reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
        reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61)
        reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:74)
        reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
        reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
        reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
        reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
        reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
        reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
        reactor.core.publisher.Mono.subscribe(Mono.java:3008)
        reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:167)
        reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
        reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
        reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61)
        reactor.ipc.netty.channel.ChannelOperations.applyHandler(ChannelOperations.java:383)
        reactor.ipc.netty.http.server.HttpServerOperations.onHandlerStart(HttpServerOperations.java:359)
        io.netty.util.concurrent.AbstractEventExecutor.safeExecute$$$capture(AbstractEventExecutor.java:163)
        io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403)
        io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463)
        io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)
    Error has been observed by the following operator(s):
        |_  Flux.map(ByteBufFlux.java:68)
        |_  Flux.doOnNext(ByteBufFlux.java:230)
        |_  Flux.map(ReactorServerHttpRequest.java:148)
        |_  Flux.flatMap(AbstractJackson2Decoder.java:95)
        |_  Flux.doFinally(AbstractJackson2Decoder.java:95)
        |_  Flux.map(AbstractJackson2Decoder.java:117)
        |_  Flux.singleOrEmpty(AbstractJackson2Decoder.java:87)
        |_  Operators.error(FluxReceive.java:276)
        |_  Mono.onErrorMap(DefaultServerRequest.java:146)
        |_  Mono.map(ConferenceService.kt:27)
        |_  Mono.map(ConferenceService.kt:32)
        |_  Mono.zipWith(ConferenceService.kt:47)
        |_  Mono.map(ConferenceService.kt:48)
        |_  Flux.flatMap(SimpleReactiveMongoRepository.java:318)
        |_  MonoExtensionsKt.toMono(ConferenceService.kt:55)
        |_  Mono.map(ConferenceService.kt:56)
        |_  Flux.map(AbstractJackson2Encoder.java:99)
        |_  Mono.flatMap(DispatcherHandler.java:177)
        |_  Mono.onErrorResume(DispatcherHandler.java:177)
        |_  Mono.flatMap(DispatcherHandler.java:161)
        |_  Mono.defer(DefaultWebFilterChain.java:71)
        |_  Mono.doOnSuccess(MetricsWebFilter.java:59)
        |_  Mono.doOnError(MetricsWebFilter.java:60)
        |_  Mono.compose(MetricsWebFilter.java:54)
        |_  Mono.defer(DefaultWebFilterChain.java:71)
        |_  Mono.defer(DefaultWebFilterChain.java:71)

回答：

`WebClient.exchange()` 结果流是单播的

实际上，这里的问题是WebClient每个连接仅允许一个订户。如果您尝试两次订阅相同的连接-

您将获得java.lang.IllegalStateException: Only one connection receive subscriber

allowed.

尽管我看不到您尝试在哪里重用同一连接两次的事实，但我相信您可以通过使用下一个运算符组合来解决该问题：

class GeoService() {
   val client = WebClient.create("https://maps.googleapis.com/maps/api/geocode/")
   fun resolveGeoFromCity(city: String): Mono<Geo> {
       return client.get()
            .uri("json?address=$city&key=$API_KEY&language=en")
            .exchange()
            .flatMap { it.bodyToMono(String::class.java) }
            .map { parse(it) }
            .share();
   }
   ...
}

在该示例中，流被配置为多播（共享）原始源，只要有至少一个Subscriber订阅源即可。如果您需要所有订阅者都收到相同的日期，可以.share用.cache运营商代替。

此外，还有一种替代上述技术的方法。您可以将上述运算符替换为处理器，并获得相同的共享可能性：

class GeoService() {
   val client = WebClient.create("https://maps.googleapis.com/maps/api/geocode/")
   fun resolveGeoFromCity(city: String): Mono<Geo> {
       return client.get()
            .uri("json?address=$city&key=$API_KEY&language=en")
            .exchange()
            .flatMap { it.bodyToMono(String::class.java) }
            .map { parse(it) }
            .subscribeWith(DirectProcessor.create());
   }
   ...
}

在这种情况下，您正好在调用之后立即订阅和运行对源数据的使用subscribeWith，因此，在这种情况下，可能会丢失部分数据，依此类推。