spring boot kotlin webflux 或 web 多文件上传报错400 415 No primary or single unique constructor found for

#当我们使用Kotlin编写Spring Boot进行多文件上传的时候，传统的方法如下：此时会有如下几种情况：以上是第一种情况，直接报错，并提示无主构造函数。这时我们通过互联网搜索可能会在形参上加上：(web)或者(webflux)。如下：然后后端没报错了，返回值却有错误：实际的原因是，在Kotlin中，List是一个不可变的数据结构，如果我们需要传入一个List，则需要使用MutableList

Ordinary_SF

6885人浏览 · 2022-08-30 09:10:24

Ordinary_SF · 2022-08-30 09:10:24 发布

#当我们使用Kotlin编写Spring Boot进行多文件上传的时候，传统的方法如下：

	//Web 的方式： 使用MultipartFile 用form-data 上传
	@PostMapping("/upload")
    @Operation(summary = "上传凭证")
    fun upload(file:List<MultipartFile>) {
        println(file.size)
    }

	//Webflux 的方式： 使用FilePart 用form-data 上传
    @PostMapping("/upload")
    fun upload( file:List<FilePart>) {
        println(file.size)
    }

此时会有如下几种情况：

java.lang.IllegalStateException: No primary or single unique constructor found for interface java.util.List
	at org.springframework.beans.BeanUtils.getResolvableConstructor(BeanUtils.java:267) ~[spring-beans-5.3.22.jar:5.3.22]
	Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException: 
Error has been observed at the following site(s):
	*__checkpoint ⇢ springfox.boot.starter.autoconfigure.SwaggerUiWebFluxConfiguration$CustomWebFilter [DefaultWebFilterChain]
	*__checkpoint ⇢ HTTP POST "/mobile/upload" [ExceptionHandlingWebHandler]
Original Stack Trace:
		at org.springframework.beans.BeanUtils.getResolvableConstructor(BeanUtils.java:267) ~[spring-beans-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.annotation.ModelAttributeMethodArgumentResolver.createAttribute(ModelAttributeMethodArgumentResolver.java:216) ~[spring-webflux-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.annotation.ModelAttributeMethodArgumentResolver.prepareAttributeMono(ModelAttributeMethodArgumentResolver.java:177) ~[spring-webflux-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.annotation.ModelAttributeMethodArgumentResolver.resolveArgument(ModelAttributeMethodArgumentResolver.java:111) ~[spring-webflux-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:119) ~[spring-webflux-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:198) ~[spring-webflux-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.InvocableHandlerMethod.invoke(InvocableHandlerMethod.java:136) ~[spring-webflux-5.3.22.jar:5.3.22]
		at org.springframework.web.reactive.result.method.annotation.RequestMappingHandlerAdapter.lambda$handle$1(RequestMappingHandlerAdapter.java:200) ~[spring-webflux-5.3.22.jar:5.3.22]
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:44) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:240) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.onComplete(MonoIgnoreThen.java:203) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoFlatMap$FlatMapMain.onComplete(MonoFlatMap.java:181) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Operators.complete(Operators.java:137) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoZip.subscribe(MonoZip.java:120) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Mono.subscribe(Mono.java:4397) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:157) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxSwitchIfEmpty$SwitchIfEmptySubscriber.onNext(FluxSwitchIfEmpty.java:74) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoNext$NextSubscriber.onNext(MonoNext.java:82) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.innerNext(FluxConcatMap.java:282) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxConcatMap$ConcatMapInner.onNext(FluxConcatMap.java:863) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onNext(FluxMapFuseable.java:129) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onNext(MonoPeekTerminal.java:180) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Operators$ScalarSubscription.request(Operators.java:2398) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.request(MonoPeekTerminal.java:139) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.request(FluxMapFuseable.java:171) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.set(Operators.java:2194) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Operators$MultiSubscriptionSubscriber.onSubscribe(Operators.java:2068) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxMapFuseable$MapFuseableSubscriber.onSubscribe(FluxMapFuseable.java:96) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoPeekTerminal$MonoTerminalPeekSubscriber.onSubscribe(MonoPeekTerminal.java:152) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoJust.subscribe(MonoJust.java:55) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Mono.subscribe(Mono.java:4397) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:451) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onSubscribe(FluxConcatMap.java:219) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:165) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.FluxIterable.subscribe(FluxIterable.java:87) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:52) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.Mono.subscribe(Mono.java:4397) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoIgnoreThen$ThenIgnoreMain.subscribeNext(MonoIgnoreThen.java:263) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoIgnoreThen.subscribe(MonoIgnoreThen.java:51) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.core.publisher.MonoDeferContextual.subscribe(MonoDeferContextual.java:55) ~[reactor-core-3.4.21.jar:3.4.21]
		at reactor.netty.http.server.HttpServer$HttpServerHandle.onStateChange(HttpServer.java:967) ~[reactor-netty-http-1.0.21.jar:1.0.21]
		at reactor.netty.ReactorNetty$CompositeConnectionObserver.onStateChange(ReactorNetty.java:677) ~[reactor-netty-core-1.0.21.jar:1.0.21]
		at reactor.netty.transport.ServerTransport$ChildObserver.onStateChange(ServerTransport.java:478) ~[reactor-netty-core-1.0.21.jar:1.0.21]
		at reactor.netty.http.server.HttpServerOperations.onInboundNext(HttpServerOperations.java:570) ~[reactor-netty-http-1.0.21.jar:1.0.21]
		at reactor.netty.channel.ChannelOperationsHandler.channelRead(ChannelOperationsHandler.java:93) ~[reactor-netty-core-1.0.21.jar:1.0.21]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at reactor.netty.http.server.HttpTrafficHandler.channelRead(HttpTrafficHandler.java:222) ~[reactor-netty-http-1.0.21.jar:1.0.21]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.CombinedChannelDuplexHandler$DelegatingChannelHandlerContext.fireChannelRead(CombinedChannelDuplexHandler.java:436) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:327) ~[netty-codec-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.handler.codec.ByteToMessageDecoder.fireChannelRead(ByteToMessageDecoder.java:314) ~[netty-codec-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.handler.codec.ByteToMessageDecoder.callDecode(ByteToMessageDecoder.java:435) ~[netty-codec-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.handler.codec.ByteToMessageDecoder.channelRead(ByteToMessageDecoder.java:279) ~[netty-codec-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.CombinedChannelDuplexHandler.channelRead(CombinedChannelDuplexHandler.java:251) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:357) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:379) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:365) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:722) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:658) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:584) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:496) ~[netty-transport-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997) ~[netty-common-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74) ~[netty-common-4.1.79.Final.jar:4.1.79.Final]
		at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30) ~[netty-common-4.1.79.Final.jar:4.1.79.Final]
		at java.base/java.lang.Thread.run(Thread.java:829) ~[na:na]

以上是第一种情况，直接报错，并提示无主构造函数。这时我们通过互联网搜索可能会在形参上加上：@RequestParam(web)或者@RequestPart(webflux)。如下：

	//Web 的方式： 使用MultipartFile 用form-data 上传
	@PostMapping("/upload")
    @Operation(summary = "上传凭证")
    fun upload(@RequestParam file:List<MultipartFile>) {
        println(file.size)
    }

	//Webflux 的方式： 使用FilePart 用form-data 上传
    @PostMapping("/upload")
    fun upload(@RequestPart file:List<FilePart>) {
        println(file.size)
    }

然后后端没报错了，返回值却有错误：

//web的报错
{
    "timestamp": "2022-08-30T00:49:42.384+00:00",
    "path": "/mobile/upload",
    "status": 400,
    "error": "Bad Request",
    "requestId": "4e33314b-1"
}
//webflux的报错
{
    "timestamp": "2022-08-30T00:53:24.607+00:00",
    "path": "/mobile/upload",
    "status": 415,
    "error": "Unsupported Media Type",
    "requestId": "34362b87-1"
}

实际的原因是，在Kotlin中，List是一个不可变的数据结构，如果我们需要传入一个List，则需要使用MutableList，其中包含了增删改的方法，可以被Spring Boot直接使用。综上，我们在代码中加入MutableList：

	//webflux
    @PostMapping("/upload")
    fun upload(@RequestPart file: MutableList<FilePart>) {
        println(file.size)
    }

此时，我们已经可以完美使用了。在这里插入图片描述

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Ordinary_SF

@Holmes_shuai

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spring boot kotlin webflux 或 web 多文件上传 报错400 415 No primary or single unique constructor found for

Ordinary_SF

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Ordinary_SF

spring boot kotlin webflux 或 web 多文件上传报错400 415 No primary or single unique constructor found for