Spring REST - Damaged/Blank File being downloaded

Question

I am trying to create a endpoint to render/serve PDF file. I have gone through the following links to build the API, but still facing some issues.

link 1

link 2

Following is my code :

byte[] targetArray = null;

InputStream is = null;

InputStream objectData = object.getObjectContent();

BufferedReader reader = new BufferedReader(new InputStreamReader(objectData));

char[] charArray = new char[8 * 1024];
StringBuilder builder = new StringBuilder();
int numCharsRead;
while ((numCharsRead = reader.read(charArray, 0, charArray.length)) != -1) {

    builder.append(charArray, 0, numCharsRead);
}
reader.close();

objectData.close();
object.close();
targetArray = builder.toString().getBytes();

is = new ByteArrayInputStream(targetArray);


return ResponseEntity.ok().contentLength(targetArray.length).contentType(MediaType.APPLICATION_PDF)
                .cacheControl(CacheControl.noCache()).header("Content-Disposition", "attachment; filename=" + "testing.pdf")
                .body(new InputStreamResource(is));

When I hit my API using postman, I am able to download PDF file but the problem is it is totally blank. What might be the issue ?

Umm... why would you read the PDF into an array of `char`, convert it to a `String`, and then extract bytes from the string? You do understand the difference between character and binary data, right? — crizzis, Apr 26 '18 at 12:22
Also, since you already have an `InputStream` to your data, why not use an `InputStreamResource` like in the first link you mentioned? — crizzis, Apr 26 '18 at 12:24
Actually I am trying to get the contents of the PDF file from a remote location which is streaming my PDF file contents. — Shivkumar Mallesappa, Apr 26 '18 at 12:26
Fair enough, but since you operate on it using an `InputStream`, that should be transparent to you. What happens when you return an `InputStreamResource` wrapping `objectData` directly? Why do you feel you need all the intermediate steps? — crizzis, Apr 26 '18 at 12:28
And If I use `InputStream ` one which is used with `object.getObjectContent();` and pass it to `InputStreamResource` I am getting a empty text file with pdf extention. — Shivkumar Mallesappa, Apr 26 '18 at 12:34
Let us [continue this discussion in chat](https://chat.stackoverflow.com/rooms/169857/discussion-between-shivkumar-mallesappa-and-crizzis). — Shivkumar Mallesappa, Apr 26 '18 at 12:36
@ShivkumarMallesappa could you please tell me how did you solve it? I am having the same issue...basically I am able to create a PDF then I use responseEntity for returning bytestream (which happens successfully but the PDF is blank) — habed, Oct 09 '18 at 15:38
@habed Did you tried the solution given below ? I have marked it as correct because I was able to stream my PDF. It worked for me. — Shivkumar Mallesappa, Oct 10 '18 at 04:56

score 1 · Accepted Answer · answered Apr 26 '18 at 13:57

There are multiple ways to download files from server, you can use ResponseEntity<InputStreamResource>, HttpServletResponse.Below are the two methods to download.

@GetMapping("/download1")
       public ResponseEntity<InputStreamResource> downloadFile1() throws IOException {

          File file = new File(FILE_PATH);
          InputStreamResource resource = new InputStreamResource(new FileInputStream(file));

          return ResponseEntity.ok()
                .header(HttpHeaders.CONTENT_DISPOSITION,
                      "attachment;filename=" + file.getName())
                .contentType(MediaType.APPLICATION_PDF).contentLength(file.length())
                .body(resource);
       }

OR

You can use StreamingResponseBody to download large files. In this case server writes data to OutputStream at same time Browser read data which means its parallel.

@RequestMapping(value = "downloadFile", method = RequestMethod.GET)
    public StreamingResponseBody getSteamingFile(HttpServletResponse response) throws IOException {
        response.setContentType("application/pdf");
        response.setHeader("Content-Disposition", "attachment; filename=\"demo.pdf\"");
        InputStream inputStream = new FileInputStream(new File("C:\\demo-file.pdf"));
        return outputStream -> {
            int nRead;
            byte[] data = new byte[1024];
            while ((nRead = inputStream.read(data, 0, data.length)) != -1) {
                System.out.println("Writing some bytes..");
                outputStream.write(data, 0, nRead);
            }
        };
    }

score 0 · Answer 2 · answered Apr 26 '18 at 12:34

You can try to use apache commons IOUtils. Why reinvent wheel :) 1. Open a connection to remote server 2. Copy the inputStream to the destination file outputStream.

public void downloadFileFromRemoteLocation(String serverlocation, File destinationFile) throws IOException
{
    try (FileOutputStream fos = new FileOutputStream( destinationFile )){
        URL url = new URL(serverlocation);
        URLConnection connection = url.openConnection();
        IOUtils.copy( connection.getInputStream(),  fos);
    } 
}

if you want to stick to just Java then look at snippet below

try {
        // Get the directory and iterate them to get file by file...
        File file = new File(fileName);

        if (!file.exists()) {
            context.addMessage(new ErrorMessage("msg.file.notdownloaded"));
            context.setForwardName("failure");
        } else {
            response.setContentType("APPLICATION/DOWNLOAD");
            response.setHeader("Content-Disposition", "attachment"+ 
                                     "filename=" + file.getName());
            stream = new FileInputStream(file);
            response.setContentLength(stream.available());
            OutputStream os = response.getOutputStream();      
            os.close();
            response.flushBuffer();
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (stream != null) {
            try {
                stream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

Spring REST - Damaged/Blank File being downloaded

2 Answers2