将对OutputStream的写入转换为ServerResponse可用的流量(&lt；DataBuffer&>

问题描述

我有一个旧库，我必须使用它来检索文件。此旧库不会像您通常期望的读取内容那样在InputStream中返回，但它希望传递给它一个开放的OutputStream，它可以写入。

我必须编写一个Webflow REST服务，将此OutputStream写入org.springframework.web.reactive.function.server.ServerResponse正文。

legacyLib.BlobRead(outputStream); // writes the stream to an outputstream, that has to be provided by me, and somehow has to end up in the ServerResponse

因为我想将Stream直接传递给ServerResponse，所以我可能必须这样做，对吗？

ServerResponse.ok().body(magicOutpuStreamToFluxConverter(), DataBuffer.class);

推荐答案

这里是RequestHandler的一部分，这很重要；我忽略了一些错误处理/异常捕获，这些错误处理/捕获通常是不需要的。注意，我为读取发布了一个不同的调度器(或者至少这是我想要做的)，这样这个阻塞读取就不会干扰我的主事件线程：

private Mono<ServerResponse> writeToServerResponse(@NotNull FPTag tag) {
    final long blobSize = tag.getBlobSize();
    return ServerResponse.ok()
        .contentType(MediaType.APPLICATION_OCTET_STREAM)
        .body(Flux.<DataBuffer>create((FluxSink<DataBuffer> emitter) -> {
      // for a really big blob I want to read it in chunks, so that my server doesn't use too much memory
      for(int i = 0; i < blobSize; i+= tagChunkSize) {
        // new DataBuffer that is written to, then emitted later
        DefaultDataBuffer dataBuffer = new DefaultDataBufferFactory().allocateBuffer();
        try (OutputStream outputStream = dataBuffer.asOutputStream()) {
          // write to the outputstream of DataBuffer
          tag.BlobReadPartial(outputStream, i, tagChunkSize, FPLibraryConstants.FP_OPTION_DEFAULT_OPTIONS);
          // don't know if flushing is strictly neccessary
          outputStream.flush();
        } catch (IOException | FPLibraryException e) {
          log.error("Error reading + writing from tag to http outputstream", e);
          emitter.error(e);
        }
        emitter.next(dataBuffer);
      }
      // if blob is finished, send "complete" to my flux of DataBuffers
      emitter.complete();
    }, FluxSink.OverflowStrategy.BUFFER).publishOn(Schedulers.newElastic("centera")).doOnComplete(() -> closeQuietly(tag)), DataBuffer.class);

}

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