Question

I had tried to develop a servlet that allow user to download file but it allow user to download the file but the file content contains binary garbage and not human readable. May I know what could be the reason ?

Code

int length = -1, index = 0;
        byte[] buffer = null;
        String attachmentPath = null, contentType = null, extension = null; 
        File attachmentFile = null;
        BufferedInputStream input = null;
        ServletOutputStream output = null;
        ServletContext context = null;

        attachmentPath = request.getParameter("attachmentPath");
        if (attachmentPath != null && !attachmentPath.isEmpty()) {
            attachmentFile = new File(attachmentPath);

            if (attachmentFile.exists()) {
                response.reset();

                context = super.getContext();  
                contentType = context.getMimeType(attachmentFile.getName());       
                response.setContentType(contentType);

                response.addHeader("content-length", String.valueOf(attachmentFile.length()));  
                response.addHeader("content-disposition", "attachment;filename=" + attachmentFile.getName());

                try {
                    buffer = new byte[AttachmentTask.DEFAULT_BUFFER_SIZE];
                    input = new BufferedInputStream(new FileInputStream(attachmentFile));
                    output = response.getOutputStream();

                    while ((length = input.read(buffer)) != -1) {
                        output.write(buffer, 0, length);
                        index += length;

//                      output.write(length);
                    }

                    output.flush();

                    input.close();
                    output.close();

                } catch (FileNotFoundException exp) {
                    logger.error(exp.getMessage());
                } catch (IOException exp) {
                    logger.error(exp.getMessage());
                }


            } else {
                try {
                    response.sendError(HttpServletResponse.SC_NOT_FOUND);
                } catch (IOException exp) {
                    logger.error(exp.getMessage());
                }
            }

It is relate to writing file as binary or text mode or browser settings?

Please help.

Thanks.

Answer 1

The problem is not in the code given so far. You’re properly using InputStream/OutputStream instead of a Reader/Writer to stream the file.

The cause of the problem is more likely in the way how you created/saved the file. This problem will manifest when you’ve used a Reader and/or Writer which is not been instructed to use the proper character encoding for the characters being read/written. Perhaps you’re creating an upload/download service and the fault was in the upload process itself?

Assuming that the data is in UTF-8, you should have created the reader as follows:

Reader reader = new InputStreamReader(new FileInputStream(file), "UTF-8"));

and the writer as follows:

Writer writer = new OutputStreamWriter(new FileOutputStream(file), "UTF-8"));

But if you actually don’t need to manipulate the stream on a per-character basis, but just wanted to transfer the data unmodified, then you should actually have used InputStream/OutputStream all the time.

See also:

• Unicode – How to get the characters right?