Download File Servlet - File Content contains binary - servlets

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?