将对 OutputStream 的写入转换为可由 ServerResponse 使用的 Flux<DataBuffer>

Question

我有一个旧库，必须使用它来检索文件。这个遗留库不会像您通常期望的那样在 InputStream 中返回读取内容，但它期望它传递一个开放的 OutputStream，以便它可以写入。

我必须编写一个 Webflux REST 服务，将该 OutputStream 写入 org.springframework.web.reactive.function.server.ServerResponse 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

由于我想将 Stream 直接传递给 ServerResponse，我可能必须做这样的事情，对吧？

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

Answer 1

这是 RequestHandler 中重要的部分。我遗漏了一些通常不需要的错误处理/异常捕获。请注意，我对读取publishedOn有不同Scheduler（或者至少，这就是我想要做的），因此这种阻塞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);
  
    }