Java Servlets Using MultipartConfig

Question

I am using a catch-all servlet and passing the request object along to other internal framework classes. Its how my application is designed. The reasons are beyond the scope of this question.

@WebServlet(name="RequestHandler", urlPatterns="/*")

I am trying to do file uploading from the browser using multipart-form-data:

<form action="" method="POST" enctype="multipart/form-data">
    <input type="file" name="file"/>
    <input type="submit" name="videoUpload" value="Upload"/>
</form>

And the only way to actually pass the file data along to the server is to annotate the servlet with:

@MultipartConfig

If I annotate my catch-all servlet, everything works fine but its not very often at all that I actually need to use the file uploading functionality.

Option 1: Leave it alone. Does leaving the annotation cause unnecessary overhead even though most of the requests don't use it?

Option 2: Add it programatically? Is there a way to programatically add the annotation if the form type of multipart is detected?

Option 3: Use the annotation elsewhere. What about using the annotation in a separate class (i'm assuming it needs to be present before the request object is actually created...)?

Answer 1

It is ok if you dont add '@MultipartConfig' annotation. You can determine programmatically if the content is multipart or not:

 String form_field="";
 FileItem fileItem = null; 
 if (ServletFileUpload.isMultipartContent(request)) {
            ServletFileUpload servletFileUpload = new ServletFileUpload(new DiskFileItemFactory());
            try {
                fileItemsList = servletFileUpload.parseRequest(request);
            } catch (FileUploadException ex) {
                out.print(ex);
            }
            String optionalFileName = "";
            Iterator it = fileItemsList.iterator();
            while (it.hasNext()) {
                FileItem fileItemTemp = (FileItem) it.next();
                if (fileItemTemp.isFormField()) {
                    if (fileItemTemp.getFieldName().equals("form_field")) {
                        form_field = fileItemTemp.getString();
                    }
                } else {
                    if (fileItemTemp.getFieldName().equals("file")) {
                        fileItem = fileItemTemp;
                    }
                }
            }
        }

If ServletFileUpload.isMultipartContent(request) is false then you can retrieve form parameters in general way by request.getParameter. I have used apache file upload in the example.