Sending File and HashMap to server in GWT

I have to send file and their properties to GWT server.

For sending a file i used form panel.

 public class BrowseFile extends DialogBox {
   // more code
   // ..

        private FormPanel getFormPanel() {
                if (formPanel == null) {
                    formPanel = new FormPanel();
                    formPanel.setMethod(FormPanel.METHOD_POST);

                    formPanel.setEncoding(FormPanel.ENCODING_MULTIPART);
                    formPanel.setAction(GWT.getHostPageBaseURL() +"UploadFileServlet");

                    formPanel.addSubmitHandler(new FormPanel.SubmitHandler(){
                        public void onSubmit(SubmitEvent event) {
                            // TODO Auto-generated method stub
                                    setFilename(fileUpload.getFilename());
                        }

                    });
                }
                return formPanel;
            }
        }   

all the properties of this file are in Hashmap

there are 2 dialog box Propertybox extends DialogBox and

BrowseFile extends DialogBox

inside the constructor of PropertyBox there is BrowseFile

When PropertyBox constructor

                setSize("600px", "670px");
    setHTML("Add Document");

    setWidget(getVerticalPanel());
    browseFile = new BrowseFile();

The custom Property inside the PropertyBox depends on the class selected (Class is tree Widget)

On Server Side

public class FileUpload extends HttpServlet implements Servlet{

    private static final long serialVersionUID = 1L;
    private static final Logger log = Logger.getLogger(FileUpload.class
            .getName());
    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException,