将输出流写入转换为可由服务器响应使用的Flux

Question

我有一个旧库，我必须使用它来检索文件。这个遗留库不会以InputStream的形式返回，正如您通常在阅读资料时所期望的那样，但它希望传递给它一个开放的OutputStream，它可以对其进行写入。

我必须编写一个WebFlow REST服务，它将此OutputStream写入org.springframework.web.reactive.function.server.服务器响应主体。

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

因为我想沿着Stream直接传递到Server响应，所以我可能必须做这样的事情，对吗？

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

Answer 1

这里是RequestHandler中重要的一部分；我遗漏了一些异常的错误处理/捕获，这些通常是不需要的。请注意，我为读取发布了不同的计划程序（或者至少，这是我想要做的），以便此阻止读取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);

}