GWT Upload/Download best practices - gwt

Question

So I am new to GWT and am not sure what the best programming practices are for what I am trying to do. In my web application the user will be able to upload a data file, my application needs to be able to access this file, do some stuff to it, and then let the user download the manipulated file.
So far I have been able to successfully upload a file with an upload servlet with this doPost method:
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
try {
DiskFileItemFactory fileItemFactory = new DiskFileItemFactory();
ServletFileUpload fileUpload = new ServletFileUpload(fileItemFactory);
fileUpload.setSizeMax(FILE_SIZE_LIMIT);
List<FileItem> items = fileUpload.parseRequest(req);
for (FileItem item : items) {
if (item.isFormField()) {
logger.log(Level.INFO, "Received form field:");
logger.log(Level.INFO, "Name: " + item.getFieldName());
logger.log(Level.INFO, "Value: " + item.getString());
} else {
logger.log(Level.INFO, "Received file:");
logger.log(Level.INFO, "Name: " + item.getName());
logger.log(Level.INFO, "Size: " + item.getSize());
}
if (!item.isFormField()) {
if (item.getSize() > FILE_SIZE_LIMIT) {
resp.sendError(HttpServletResponse.SC_REQUEST_ENTITY_TOO_LARGE, "File size exceeds limit");
return;
}
String fileName = item.getName();
if (fileName != null) {
fileName = FilenameUtils.getName(fileName);
}
fileName = getServletContext().getRealPath("/uploadedFiles/" + fileName);
byte[] data = item.get();
FileOutputStream fileOutSt = new FileOutputStream(fileName);
fileOutSt.write(data);
fileOutSt.close();
if (!item.isInMemory())
item.delete();
}
}
} catch (Exception e) {
logger.log(Level.SEVERE, "Throwing servlet exception for unhandled exception", e);
throw new ServletException(e);
}
}
When I look in my war folder, the uploadedFiles folder is created successfully and files are put there.
At this point I am a bit stuck, I have been researching but cannot seem to find a clear concise answer on what is the best way for me to access the uploaded files on the client side in order to manipulate them and then allow the user to download them. Maybe I am approaching this wrong, I am not sure. If someone could point me in the right direction or show me some good examples of the right way to do things that would be great, thanks.

Answer 1

To access the file in client side you need a new servlet or the same you are using with a doGet method.
The client should ask for the file via an Anchor or an Image depending on the file type but adding a parameter so as the server is able to identify the file. Normally you can use the name of the FileInput you used for uploading or maybe you could return a tag from the server.
I would recommend to you to take a try to gwt-upload, it would save a lot of time to you.

Answer 2

I solved my problem. When the file was successfully uploaded, I stored the file name. Later I used a RPC to access the file on the server. I passed the file name to the RPC so that it knows what file I am working on, then it looks for that file in the upload folder. So I can create the java file like this,
File file = new File((this.getServletContext().getRealPath("uploadedFiles") + File.separator + fileName));
and manipulate it how I see fit.