Downloading a file from spring controllers

Question

I have a requirement where I need to download a PDF from the website. The PDF needs to be generated within the code, which I thought would be a combination of freemarker and

Answer 1

If you:

• Don't want to load the whole file into a byte[] before sending to the response;
• Want/need to send/download it via InputStream;
• Want to have full control of the Mime Type and file name sent;
• Have other @ControllerAdvice picking up exceptions for you (or not).

The code below is what you need:

@RequestMapping(value = "/stuff/{stuffId}", method = RequestMethod.GET)
public ResponseEntity downloadStuff(@PathVariable int stuffId)
                                                                      throws IOException {
    String fullPath = stuffService.figureOutFileNameFor(stuffId);
    File file = new File(fullPath);
    long fileLength = file.length(); // this is ok, but see note below

    HttpHeaders respHeaders = new HttpHeaders();
    respHeaders.setContentType("application/pdf");
    respHeaders.setContentLength(fileLength);
    respHeaders.setContentDispositionFormData("attachment", "fileNameIwant.pdf");

    return new ResponseEntity(
        new FileSystemResource(file), respHeaders, HttpStatus.OK
    );
}

About the file length part: File#length() should be good enough in the general case, but I thought I'd make this observation because it does can be slow, in which case you should have it stored previously (e.g. in the DB). Cases it can be slow include: if the file is large, specially if the file is in a remote system or something more elaborated like that - a database, maybe.

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InputStreamResource

If your resource is not a file, e.g. you pick the data up from the DB, you should use InputStreamResource. Example:

    InputStreamResource isr = new InputStreamResource(new FileInputStream(file));
    return new ResponseEntity(isr, respHeaders, HttpStatus.OK);