如何在 Spring WebFlux 中从 Multipart/form-data 流式传输文件

Question

我想从客户端（例如前端）接收 Multipart/form-data。然后将表单数据的文件内容流式传输到另一个后端服务。

现在我可以读取整个文件并通过 byte[]（base64 字符串）将其传递到某处，如下所示：

@PostMapping(consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public Mono<ResponseType> upload(@RequestPart("document") FilePart document, 
                                 @RequestPart("stringParam") String stringParam) {
    return service.upload(document, stringParam);
}

// Casually convert to single byte array...
private Mono<byte[]> convertFilePartToByteArray(FilePart filePart) {
    return Mono.from(filePart
            .content()
            .map(dataBuffer -> {
                byte[] bytes = new byte[dataBuffer.readableByteCount()];
                dataBuffer.read(bytes);
                DataBufferUtils.release(dataBuffer);

                return bytes;
            }));
}

这种方法存在一些问题：

我不想将整个文件读入内存；
数组大小限制为 Integer.MAX_VALUE;
数组编码为base64字符串，占用额外内存；
由于我将整个数组放入 Mono - “spring.codec.max-in-memory-size”必须大于数组大小。

我已经尝试通过 WebClientBuilder 的 asyncPart 发送文件：

MultipartBodyBuilder builder = new MultipartBodyBuilder();
builder.asyncPart("document", document.content(), DataBuffer.class);

但是我收到一个错误：

java.lang.IllegalStateException: argument type mismatch
Method [public reactor.core.publisher.Mono<> upload(**org.springframework.http.codec.multipart.FilePart**,java.lang.String)] with argument values:
[0] [type=**org.springframework.http.codec.multipart.DefaultParts$DefaultFormFieldPart**]

UPD：完整代码，生成错误

// External controller for client.
@PostMapping(consumes = MediaType.MULTIPART_FORM_DATA_VALUE, value = "/v2")
public Mono<DocumentUploadResponse> uploadV2(@RequestPart("document") FilePart document,
                                             @RequestPart("stringParam") String stringParam) {
    MultipartBodyBuilder builder = new MultipartBodyBuilder();
    builder.asyncPart("document", document.content(), DataBuffer.class);
    builder.part("stringParam", stringParam);

    WebClient webClient = webClientBuilder.build();
    return webClient.post()
            .uri("URL_TO_ANOTHER_SERVICE")
            .contentType(MediaType.MULTIPART_FORM_DATA)
            .body(BodyInserters.fromMultipartData(builder.build()))
            .retrieve()
            .bodyToMono(FileMetaDto.class)
            .map(DocumentUploadResponse::new);
}

// Internal service controller.
@PostMapping(path = "/upload/v2", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public Mono<FileMetaDto> upload(@RequestPart("document") FilePart document,
                                @RequestPart("stringParam") String stringParam) {
    return ...;
}

Answer 1

看起来我成功地传输了文件，工作代码如下：

// External controller for client.
@PostMapping(consumes = MediaType.MULTIPART_FORM_DATA_VALUE, value = "/v2")
public Mono<DocumentUploadResponse> uploadV2(@RequestPart("document") FilePart document,
                                             @RequestPart("stringParam") String stringParam) {
    MultipartBodyBuilder builder = new MultipartBodyBuilder();
    builder.asyncPart("document", document.content(), DataBuffer.class).filename(document.filename());
    builder.part("stringParam", stringParam);

    WebClient webClient = webClientBuilder.build();
    return webClient.post()
            .uri("URL_TO_ANOTHER_SERVICE")
            .contentType(MediaType.MULTIPART_FORM_DATA)
            .body(BodyInserters.fromMultipartData(builder.build()))
            .retrieve()
            .bodyToMono(FileMetaDto.class)
            .map(DocumentUploadResponse::new);
}

// Internal service controller.
@PostMapping(path = "/upload/v2", consumes = MediaType.MULTIPART_FORM_DATA_VALUE)
public Mono<FileMetaDto> upload(@RequestPart("document") FilePart document,
                                @RequestPart("stringParam") String stringParam) {
    return ...;
}

在我遗漏的原始问题代码中：
builder.asyncPart("文档", document.content(), DataBuffer.class).filename(document.filename());

如何在 Spring WebFlux 中从 Multipart/form-data 流式传输文件

How to stream file from Multipart/form-data in Spring WebFlux

java

spring

spring-webflux