GWT - File Upload

I am trying to do file upload on GWT, I search through internet and unfortunately, I found no way of doing file uploads with RPC :-(

Solution i found still back to common HTTP upload, just tweak a little to fit into the GWT environment.
I post the solution here which mixed used of widget in GWT and GXT.
Please drop me a comment if you know of a better way, or way to improve what I have done.

GWT Part
1. FormPanel(GWT or GXT) must be used in order to upload.
2. Must set the Action by setAction();
3. Must set encoding to Encoding.Multipart;
4. Must use method POST;

final FormPanel formPanel = new FormPanel();
String action = GWT.getModuleBaseURL() + "uploadFile";
formPanel.setLabelWidth(150);
formPanel.setEncoding(Encoding.MULTIPART);
formPanel.setMethod(Method.POST);
formPanel.setAction(action);
formPanel.setFrame(true);
formPanel.setHeaderVisible(false);
			
// file upload field , set the name.		
FileUploadField imageUploadField = new FileUploadField();
imageUploadField.setFieldLabel("Change Picture");
mageUploadField.setName("uplodapic");
formPanel.add(imageUploadField);
		
Button submitButton = new Button("Submit");
submitButton.addSelectionListener(new SelectionListener()
{
	@Override
	public void componentSelected(ComponentEvent ce)
	{
		formPanel.submit();		// call form submit for submit.			
	}
});
			
formPanel.addButton(submitButton);

formPanel.addFormHandler(new FormHandler() 
{
         public void onSubmitComplete(FormSubmitCompleteEvent event) 
         {
	        // When the form submission is successfully completed, this
	        // event is fired. Assuming the service returned a response of type
	        // text/html, we can get the result text here 
	        Window.alert(event.getResults());
          }

	  public void onSubmit(FormSubmitEvent event) 
          {
	        // TODO Auto-generated method stub
	  }
});			

Then add following lines to your XXXXX.gwt.xml

<servlet path="/uploadFile" class="com.server.FileUploadImpl"/>

Part 2 - Servlet
This servlet implementation used apache common file upload library and follow guide line in apache site.

public class FileUploadImpl extends HttpServlet
{
	private static final long serialVersionUID = 8305367618713715640L;
	@Override
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
	{
		response.setContentType("text/plain");
		System.out.println("Inside File Upload Servlet...............>>>>>>>>>>");
		try
		{
			getFileItem(request);
			response.getWriter().write(new String("Uploading Completed...."));
		}
		catch(Exception e)
		{
			e.printStackTrace();
			System.out.println(e.getMessage());
		}
	}

	private FileItem getFileItem(final HttpServletRequest request)
	{
		FileItemFactory factory = new DiskFileItemFactory();
		ServletFileUpload upload = new ServletFileUpload(factory);
		// Create a progress listener, if want to use
		ProgressListener progressListener = new ProgressListener()
		{
			private long megaBytes = -1;
			int i = -1;

			public void update(long pBytesRead, long pContentLength, int pItems)
			{
				if(i != pItems)
				{
					i = pItems;
					System.out.println("Setting TotalSize " + pContentLength);
					System.out.println("We are currently reading item " + pItems);
				}
				long mBytes = pBytesRead / 10000;
				if(megaBytes == mBytes)
				{
					return;
				}
				megaBytes = mBytes;
				if(pContentLength == -1)
				{
					System.out.println("So far, " + pBytesRead + " bytes have been read.");				
				}
				else
				{
					System.out.println("Read, " + pBytesRead + " of " + pContentLength + " bytes.");
				}
			}
		};
		upload.setProgressListener(progressListener);

		try
		{
			List items = upload.parseRequest(request);
			System.out.println("List Items, size --->" + items.size());
			Iterator it = items.iterator();
			while(it.hasNext())
			{
				FileItem item = (FileItem) it.next();
				if(item.isFormField())
				{
					System.out.println("File String->" + item.getString());
				}
				else
				{
					System.out.println(String.format("File Name-> %s, Size-> %s, Content Type->%s, Isformfield-> %s, inMemory-> %s",
                                                   item.getFieldName(), item.getSize(), item.getContentType(), item.isFormField(), item.isInMemory()));
					this.processUpload(item);
				}
			}
		}
		catch(Exception e)
		{
			e.printStackTrace();
			System.out.println(e.toString());
			return null;
		}
		return null;
	}

	private void processUpload(FileItem uploadItem)
	{
		try
		{
			InputStream input = uploadItem.getInputStream();
			byte[] fileContents = uploadItem.get();
			// TODO: add code to process file contents here.
			// Process a file upload
			/*
			 * if (writeToFile) { 
			 * File uploadedFile = new File(...);
			 * item.write(uploadedFile); 
			 * } 
			 * else 
			 * { 
			 * InputStream uploadedStream =
			 * item.getInputStream(); 
			 * uploadedStream.close(); 
			 * }
			 */
		}
		catch (IOException e)
		{
			e.printStackTrace();
		}
	}
}

So this should able to let you upload file from the GWT and process and the back end.