How to serve files/PDF files the reactive way in spring

I have the following endpoint code to serve PDF files.

@RequestMapping
ResponseEntity<byte[]> getPDF() {
  File file = ...;
  byte[] contents = null;
  try {
    try (FileInputStream fis = new FileInputStream(file)) {
      contents = new byte[(int) file.length()];
      fis.read(contents);
    }
  } catch(Exception e) {
    // error handling
  }
  HttpHeaders headers = new HttpHeaders();
  headers.setContentDispositionFormData(file.getName(), file.getName());
  headeres.setCacheControl("must-revalidate, post-check=0, pre-check=0");
  return new ResponseEntity<>(contents, headers, HttpStatus.OK);
}

How can I convert above into a reactive type Flux/Mono and DataBuffer.

I have check DataBufferUtils but It doesn’t seem to offer what I needed. I didn’t find any example either.

Answer

The easiest way to achieve that would be with a Resource.

@GetMapping(path = "/pdf", produces = "application/pdf")
ResponseEntity<Resource> getPDF() {
  Resource pdfFile = ...;
  HttpHeaders headers = new HttpHeaders();
  headers.setContentDispositionFormData(file.getName(), file.getName());
  return ResponseEntity
    .ok().cacheControl(CacheControl.noCache())
    .headers(headers).body(resource);
}

Note that DataBufferUtils has some useful methods there that convert an InputStream to a Flux<DataBuffer>, like DataBufferUtils#read(). But dealing with a Resource is still superior.