Question

I am using COS multipart to handle file upload on the servlet.

When processing the parts i need to rename the file with an extra posted field (ParamPart), in this case ‘artikelcode’ needs to be prepended to the filename.

So instead of directly writing the FilePart to disk i need to save the inputstream in memory.

This is the code i have so far:

MultipartParser multipartParser = new MultipartParser(request, 100000000);
                String artikelcode = null;
                String filename = null;
                InputStream in = null;

                while ((part = multipartParser.readNextPart()) != null) {
                    if (part.isFile()) {
                        FilePart filePart = (FilePart) part;
                        filename = filePart.getFileName();
                        //long fileSize = filePart.writeTo(new File(fileSavePath));
                        if (filename != null) in = filePart.getInputStream();
                    }

                    if (part.isParam()) {
                        ParamPart paramPart = (ParamPart) part;
                        if (paramPart.getName().equals("artikelcode")) artikelcode = paramPart.getStringValue();
                    }
                }

                if (in != null)
                {
                    String fileSavePath =  "c:\\upload\\"+artikelcode+"_"+filename;
                    File file = new File(fileSavePath);
                    OutputStream out = new FileOutputStream(file);
                    IOUtils.copy(in, out);
                    out.close();
                }

When the file is saved on disk, it is empty!

Thanks for your help!!

Answer 1

Calling readNextPart() invalidates any data that you got from the previous part.

Here is a better approach: Always save the file with a temporary name and then rename it.

This allows you to handle a lot of common errors graciously like: Disk full, errors while saving, etc. because you never overwrite existing files until you are 100% sure the new file is complete.