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我正在使用Spring Boot 2.0.0.M7和Project Reactor。我的问题涉及编写单元测试时遇到的一些奇怪的行为。在尝试将flatMap的输出提供给存储库时，我也遇到了这个问题。Reactor - 在flatMap的输出上调用块会导致ClassCastException
Mono<Foo> create(Mono<FooResource> resourceMono) {
resourceMono.flatMap({
// convert resource into Foo domain Entity
return new Foo()
})
}
该闭合应该发出Mono<Foo>由于flatMap返回值。但是，调用block()时认购并获得所产生的Foo，有一个ClassCastException在FluxFlatMap.trySubscribeScalarMap
测试代码：
def createdFoo = Foo.create(Mono.just(fooResource)).block()
堆栈跟踪：
java.lang.ClassCastException: com.example.Foo cannot be cast to org.reactivestreams.Publisher
at reactor.core.publisher.FluxFlatMap.trySubscribeScalarMap(FluxFlatMap.java:141)
at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:53)
at reactor.core.publisher.Mono.block(Mono.java:1161)
这似乎发生，因为MonoJust工具Callable，所以trySubscribeScalarMap试图解开它不成功。
在非测试案例场景中，会发生类似的错误。
Mono<ServerResponse> createFoo(ServerRequest request) {
def body = request.body(BodyExtractors.toMono(FooResource))
ok().body(fromPublisher(Foo.create(body)
.flatMap({fooRepository.save(it)}), Foo))
}
堆栈跟踪：
java.lang.ClassCastException: com.example.Foo cannot be cast to reactor.core.publisher.Mono
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:118) [reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
at reactor.core.publisher.FluxOnAssembly$OnAssemblySubscriber.onNext(FluxOnAssembly.java:450) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
at reactor.core.publisher.Operators$MonoSubscriber.complete(Operators.java:1092) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
at reactor.core.publisher.MonoSingle$SingleSubscriber.onComplete(MonoSingle.java:171) ~[reactor-core-3.1.2.RELEASE.jar:3.1.2.RELEASE]
<...>
Assembly trace from producer [reactor.core.publisher.MonoFlatMap] :
reactor.core.publisher.Mono.flatMap(Mono.java:2059)
org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoCachedMethodSiteNoUnwrap.invoke(PojoMetaMethodSite.java:213)
org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
com.example.Foo.create(Foo.groovy:28)
org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125)
com.example.FooHandlerFunctions.createFoo(FooHandlerFunctions.groovy:48)
中包装flatMap封闭的输出在另一Mono.just(foo)解决了这两个问题。但是，这似乎不应该需要。我做错了什么，或者只是误解flatMap在这里工作？