Bean validation in WebFlux does not work when using BindingResult in the controller's action

[Petitt88]

I've tried to use bean validation in Spring WebFlux but the request fails somewhere in the Netty pipeline if I specifiy "BindingResult bindingResult" parameter in the controller's action.

The very same code works fine with normal Spring Mvc.
Attached a sample project here.

Repro steps:

1. just send a POST request to http://localhost:8080/ with request's "Content-Type: application/json" header and let the payload be empty json ({}) --> the exception is thrown.

This is the stacktrace:

java.lang.IllegalStateException: Failed to resolve argument 1 of type 'org.springframework.validation.BindingResult' on public com.example.demojavawebflux.Movie com.example.demojavawebflux.DemoJavaWebfluxApplication.post(com.example.demojavawebflux.Movie,org.springframework.validation.BindingResult)
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.getArgumentError(InvocableHandlerMethod.java:228) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.resolveArg(InvocableHandlerMethod.java:223) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.lambda$null$1(InvocableHandlerMethod.java:179) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at java.util.Optional.orElseGet(Optional.java:267) ~[na:1.8.0_152]
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.lambda$resolveArguments$2(InvocableHandlerMethod.java:177) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193) ~[na:1.8.0_152]
	at java.util.Spliterators$ArraySpliterator.forEachRemaining(Spliterators.java:948) ~[na:1.8.0_152]
	at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481) ~[na:1.8.0_152]
	at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471) ~[na:1.8.0_152]
	at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708) ~[na:1.8.0_152]
	at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234) ~[na:1.8.0_152]
	at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499) ~[na:1.8.0_152]
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.resolveArguments(InvocableHandlerMethod.java:183) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:136) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerAdapter.lambda$handle$1(RequestMappingHandlerAdapter.java:196) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:148) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:74) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoPeekFuseable.subscribe(MonoPeekFuseable.java:74) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:150) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:67) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:76) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:271) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:798) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:115) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:1649) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:156) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:1463) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:1337) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:90) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:54) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoMapFuseable.subscribe(MonoMapFuseable.java:59) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.Mono.subscribe(Mono.java:2913) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:418) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:210) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:91) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:55) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.FluxConcatMap.subscribe(FluxConcatMap.java:121) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoNext.subscribe(MonoNext.java:40) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoSwitchIfEmpty.subscribe(MonoSwitchIfEmpty.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoFlatMap.subscribe(MonoFlatMap.java:60) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.Mono.subscribe(Mono.java:2913) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.drain(MonoIgnoreThen.java:167) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:56) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoOnErrorResume.subscribe(MonoOnErrorResume.java:44) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.core.publisher.MonoPeekTerminal.subscribe(MonoPeekTerminal.java:61) ~[reactor-core-3.1.1.RELEASE.jar:3.1.1.RELEASE]
	at reactor.ipc.netty.channel.ChannelOperations.applyHandler(ChannelOperations.java:388) ~[reactor-netty-0.7.1.RELEASE.jar:0.7.1.RELEASE]
	at reactor.ipc.netty.http.server.HttpServerOperations.onHandlerStart(HttpServerOperations.java:359) ~[reactor-netty-0.7.1.RELEASE.jar:0.7.1.RELEASE]
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute$$$capture(AbstractEventExecutor.java:163) ~[netty-common-4.1.16.Final.jar:4.1.16.Final]
	at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java) ~[netty-common-4.1.16.Final.jar:4.1.16.Final]
	at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:403) ~[netty-common-4.1.16.Final.jar:4.1.16.Final]
	at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:463) ~[netty-transport-4.1.16.Final.jar:4.1.16.Final]
	at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:858) ~[netty-common-4.1.16.Final.jar:4.1.16.Final]
	at java.lang.Thread.run(Thread.java:748) ~[na:1.8.0_152]
Caused by: java.lang.NullPointerException: null
	at org.springframework.web.reactive.result.method.annotation.ErrorsMethodArgumentResolver.resolveArgument(ErrorsMethodArgumentResolver.java:63) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	at org.springframework.web.reactive.result.method.InvocableHandlerMethod.resolveArg(InvocableHandlerMethod.java:214) ~[spring-webflux-5.0.1.RELEASE.jar:5.0.1.RELEASE]
	... 58 common frames omitted
[demo-java-webflux.zip](https://github.com/spring-projects/spring-boot/files/1452182/demo-java-webflux.zip)

[snicoll]

Attached a sample project.

I think you forgot to actually reference it.

[Petitt88]

Whoops sorry, I added the link.

[wilkinsona]

Thanks. This looks like a Spring WebFlux issue to me. BindingAwareConcurrentModel is empty so the call to get("org.springframework.validation.BindingResult.movie") returns null. As a result, the NullPointerException occurs when getClass() is called on the result.

@rstoyanchev Could you take a look please?

[rstoyanchev]

BindingResult after @RequestBody is currently not supported in WebFlux so that's a feature request. Separately we do need to fix the NPE in ErrorsMethodArgumentResolver which is a bug.

Validation should still work, i.e. if the BindingResult argument is removed I would expect a WebExchangeBindException and a 400 response.

[wilkinsona]

Thanks, @rstoyanchev.

Validation should still work, i.e. if the BindingResult argument is removed I would expect a WebExchangeBindException and a 400 response.

Confirmed. With the suggested changes made to the sample, a 400 response is received:

$ curl -X POST http://localhost:8080 -H "Content-Type: application/json" -d '{}'
{"timestamp":1510245196853,"path":"/","message":"Validation failed for argument at index 0 in method: public com.example.demojavawebflux.Movie com.example.demojavawebflux.DemoJavaWebfluxApplication.post(com.example.demojavawebflux.Movie), with 1 error(s): [Field error in object 'movie' on field 'name': rejected value [null]; codes [NotNull.movie.name,NotNull.name,NotNull.java.lang.String,NotNull]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [movie.name,name]; arguments []; default message [name]]; default message [must not be null]] ","errors":[{"codes":["NotNull.movie.name","NotNull.name","NotNull.java.lang.String","NotNull"],"arguments":[{"codes":["movie.name","name"],"arguments":null,"defaultMessage":"name","code":"name"}],"defaultMessage":"must not be null","objectName":"movie","field":"name","rejectedValue":null,"bindingFailure":false,"code":"NotNull"}],"status":400,"error":"Bad Request"}

@Petitt88 Could you please raise a Spring Framework JIRA ticket for the NPE and perhaps for the required enhancement too?

[rstoyanchev]

I've created and fixed https://jira.spring.io/browse/SPR-16187 for the NPE.

@Petitt88, declare the argument with a reactive type, e.g. @Valid @RequestBody Mono<Movie> movie and then use one of the onErrorXxx operators to handle a WebExchangeBindException error signal.

I think this is the most fitting solution on the WebFlux side for access to request body errors inside the controller method. Keep in mind the request body could also be a Flux. A BindingResult argument in that case cannot be provided since the Flux is yet to be consumed, and with a Mono<BindingResult> you'd have be careful to use the Flux for the body first and then check the Mono for the errors which makes no sense. Instead we have one consistent advice which is to use the onError operators on the Mono or Flux for the request body, that is if you want to handle the exception in the controller method.

[easmith]

@rstoyanchev
Server send only 400 code and empty body.
I would like send 400 http code and some message about the validation.
How can I handle WebExchangeBindException?
Implementing WebExceptionHandler does not work :(