background
I was going to implement graceful shutdown for my project (http using webclient), and when I tried to shutdown my application, many http tasks would be still put into the queue of webclient. and I would like to execute completely these http request as best as it can, but PrematureCloseException would encounter at this time.

o.s.w.r.f.c.WebClientRequestException: Connection prematurely closed BEFORE response
    at o.s.w.r.f.c.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:136)
    Suppressed: r.c.p.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
    *__checkpoint ⇢ Request to PUT http://xxx [DefaultWebClient]
Original Stack Trace:
        at o.s.w.r.f.c.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:136)
        at r.c.p.MonoErrorSupplied.subscribe(MonoErrorSupplied.java:55)
        at r.c.p.Mono.subscribe(Mono.java:4568)
        at r.c.p.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
        at r.c.p.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
        at r.c.p.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
        at r.c.p.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
        at r.c.p.MonoNext$NextSubscriber.onError(MonoNext.java:93)
        at r.c.p.MonoFlatMapMany$FlatMapManyMain.onError(MonoFlatMapMany.java:205)
        at r.c.p.SerializedSubscriber.onError(SerializedSubscriber.java:124)
        at r.c.p.FluxRetryWhen$RetryWhenMainSubscriber.whenError(FluxRetryWhen.java:229)
        at r.c.p.FluxRetryWhen$RetryWhenOtherSubscriber.onError(FluxRetryWhen.java:279)
        at r.c.p.FluxContextWrite$ContextWriteSubscriber.onError(FluxContextWrite.java:121)
        at r.c.p.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.maybeOnError(FluxConcatMapNoPrefetch.java:327)
        at r.c.p.FluxConcatMapNoPrefetch$FluxConcatMapNoPrefetchSubscriber.onNext(FluxConcatMapNoPrefetch.java:212)
        at r.c.p.FluxContextWrite$ContextWriteSubscriber.onNext(FluxContextWrite.java:107)
        at r.c.p.SinkManyEmitterProcessor.drain(SinkManyEmitterProcessor.java:476)
        at r.c.p.SinkManyEmitterProcessor$EmitterInner.drainParent(SinkManyEmitterProcessor.java:620)
        at r.c.p.FluxPublish$PubSubInner.request(FluxPublish.java:874)
        at r.c.p.FluxContextWrite$ContextWriteSubscriber.request(FluxContextWrite.java:136)
        ... 42 frames truncated
Caused by: r.n.h.c.PrematureCloseException: Connection prematurely closed BEFORE response

I’m not sure why this error encountered, after some investigation, I guessed the connection would be closed by netty when the application got the shutdown signal once, handled in the org.springframework.http.client.ReactorResourceFactory#stop.

although I have implemented the graceful shutdown method for my own logic like :
@Bean(initMethod = "start", destroyMethod = "shutdown")
but during debug, the error already encountered always before the execution of destroyMethod = "shutdown"

below is the bean of the webclient:

@Bean(name = "webClient")
    public WebClient webClient(WebClient.Builder builder) {
        HttpClient httpClient = HttpClient.create().responseTimeout(5);
        return builder.clientConnector(new ReactorClientHttpConnector(httpClient)).build();
    }

Question
how can I avoid this error so that I can make it best to complete the http requests to achieve the graceful shutdown