Question

I am trying to fully implement a resumable file upload system in Java. The library I am using is resumable.js which sends chunks of a file to save as .part and then merge them together at the end. When I receive the POST request, in my doPost method I take the request, save it into a HttpServletRequestWrapper and then use that to get all the data I need. However, when saving the files as .part I end up with them being empty and have a size of 0 bytes.

I have checked and it seems that the data is all there, but I can’t seem to get the data to save. Is there something that I implemented incorrectly?

Here is a small snippet of the code I use to do this task:

public void doPost(HttpServletRequest request, HttpServletResponse response) {
    try {
        HttpServletRequestWrapper wrapReq = new HttpServletRequestWrapper(request);
        BufferedReader reader = wrapReq.getReader();
        /**
        * Get some data from the BufferedReader
        */
        if(ServletFileUpload.isMultipartContent(wrapReq)){
            File mkd = new File(temp_dir);
            if(!mkd.isDirectory())
                mkd.mkdirs();

            DiskFileItemFactory factory = new DiskFileItemFactory();
            ServletFileUpload upload = new ServletFileUpload(factory);
            Iterator<FileItem> iter = upload.parseRequest(request).iterator();
            OutputStream out;

            out = new FileOutputStream(new File(dest_dir));
            while(iter.hasNext()){
                try {

                    FileItem item = iter.next();
                    IOUtils.copy(item.getInputStream(), out);                       
                    logger.debug("Wrote file " + resumableIdentifier + " with chunk number "
                            + resumableChunkNumber + " to " + temp_dir);
                    out.close();
                } catch (FileNotFoundException fnfe) {
                    fnfe.printStackTrace();
                }
            }
        }
        tryCreateFileFromChunks(temp_dir, resumableFileName, resumableChunkSize, resumableTotalSize);

    } catch (Exception e) {
        e.printStackTrace();
    }
}

Where the tryCreateFileFromChunks() method just checks if all the parts are there and merges them. It isn’t the problem. The .part files themselves are being stored empty.

So, did I handle this the wrong way? I’ve been struggling to get this working correctly.

Answer 1

You shouldn’t be using HttpServletRequestWrapper, nor be calling its getReader(). The request body can be read only once and you’ve to choose whether to use getReader() method, or getInputStream() method, or getParameterXxx() methods on the very same request and not mix them.

Apache Commons FileUpload uses internally getInputStream() to parse the request body. But if you’ve called getReader() or getParameterXxx() beforehand, then Apache Commons FileUpload will get an empty request body.

All with all, to fix your problem, just get rid of wrapReq altogether.

if(ServletFileUpload.isMultipartContent(request)){
    // ...

See also:

• How to upload files to server using JSP/Servlet?