Spring 5 在其响应式特性中支持 Java 9 Flow APIs？

Question

在 Spring 5.0.0.RC4 引用文档中，它说:

Publisher or Flow.Publisher — any type implementing Reactive Streams Publisher is supported.

https://docs.spring.io/spring/docs/5.0.0.RC4/spring-framework-reference/reactive-web.html#webflux

但是当我基于Spring 5.0.0.RC4创建一个简单的项目时，返回 Flow.Publisher却失败了在 Controller 中。看来 Flow.Publisher jackson 无法序列化。

org.springframework.core.codec.CodecException: Type definition error: [simple type, class java.util.concurrent.ForkJoinPool$DefaultForkJoinWorkerThreadFactory]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class java.util.concurrent.ForkJoinPool$DefaultForkJoinWorkerThreadFactory and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.concurrent.SubmissionPublisher["executor"]->java.util.concurrent.ForkJoinPool["factory"])
at org.springframework.http.codec.json.AbstractJackson2Encoder.encodeValue(AbstractJackson2Encoder.java:132)
at org.springframework.http.codec.json.AbstractJackson2Encoder.lambda$encode$0(AbstractJackson2Encoder.java:96)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:107)
at reactor.core.publisher.FluxJust$WeakScalarSubscription.request(FluxJust.java:91)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:156)
at org.springframework.http.server.reactive.ChannelSendOperator$WriteBarrier.onSubscribe(ChannelSendOperator.java:143)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)
at reactor.core.publisher.FluxJust.subscribe(FluxJust.java:68)
at reactor.core.publisher.FluxMapFuseable.subscribe(FluxMapFuseable.java:63)
at org.springframework.http.server.reactive.ChannelSendOperator.subscribe(ChannelSendOperator.java:76)
at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:150)
at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1068)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onNext(MonoFlatMap.java:241)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onNext(FluxOnErrorResume.java:72)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:198)
at reactor.core.publisher.FluxPeekFuseable$PeekFuseableSubscriber.onNext(FluxPeekFuseable.java:198)
at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1068)
at reactor.core.publisher.MonoIgnoreThen$ThenAcceptInner.onNext(MonoIgnoreThen.java:290)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:1625)
at reactor.core.publisher.MonoIgnoreThen$ThenAcceptInner.onSubscribe(MonoIgnoreThen.java:279)
at reactor.core.publisher.FluxFlatMap.trySubscribeScalarMap(FluxFlatMap.java:161)
at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:53)
at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:148)
at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
at reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:74)
at reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:74)
at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:150)
at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67)
at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:76)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:271)
at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:798)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:115)
at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:1625)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:156)
at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:1439)
at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:1313)
at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90)
at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:54)
at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59)
at reactor.core.publisher.Mono.subscribe(Mono.java:2757)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:418)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:210)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:91)
at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:55)
at reactor.core.publisher.FluxConcatMap.subscribe(FluxConcatMap.java:121)
at reactor.core.publisher.MonoNext.subscribe(MonoNext.java:40)
at reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44)
at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60)
at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60)
at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
at reactor.core.publisher.Mono.subscribe(Mono.java:2757)
at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:167)
at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56)
at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44)
at reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61)
at reactor.ipc.netty.channel.ChannelOperations.applyHandler(ChannelOperations.java:380)
at reactor.ipc.netty.http.server.HttpServerOperations.onHandlerStart(HttpServerOperations.java:354)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:163)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class java.util.concurrent.ForkJoinPool$DefaultForkJoinWorkerThreadFactory and no properties discovered to create BeanSerializer (to avoid exception, disable SerializationFeature.FAIL_ON_EMPTY_BEANS) (through reference chain: java.util.concurrent.SubmissionPublisher["executor"]->java.util.concurrent.ForkJoinPool["factory"])
at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:77)
at com.fasterxml.jackson.databind.SerializerProvider.reportBadDefinition(SerializerProvider.java:1191)
at com.fasterxml.jackson.databind.DatabindContext.reportBadDefinition(DatabindContext.java:312)
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:71)
at com.fasterxml.jackson.databind.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:33)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727)
at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:719)
at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:155)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480)
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319)
at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.serialize(ObjectWriter.java:1396)
at com.fasterxml.jackson.databind.ObjectWriter._configAndWriteValue(ObjectWriter.java:1120)
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:950)
at org.springframework.http.codec.json.AbstractJackson2Encoder.encodeValue(AbstractJackson2Encoder.java:129)
... 65 common frames omitted

更新 1 : 完整版 source codes for Java 9 .

@GetMapping
public Flow.Publisher<Post> all() {
    SubmissionPublisher publisher = new SubmissionPublisher();
    publisher.submit(new Post(1L, "post one", "content of post one"));
    publisher.submit(new Post(2L, "post two", "content of post two"));

    return publisher;
}

更新 2 : 在 Spring 5.0.0.RELEASE 的引用文档中，我找不到那里的声明。

更新 3 : 更新了Spring 5.0.2(由Spring Boot 2.0.0.M7管理)，代码运行良好，无异常，但访问时会阻塞请求。检查我更新的 sample codes .

Answer 1

确实，目前不支持此功能。

请订阅问题SPR-16052知道什么时候可用。