How to render Velocity template after file upload?

Hi, I have a plugin that allows users to upload a csv file. After the upload is completed, I would like the plugin to render a velocity template that says upload successful. How do I do so?

Servlet class:

public class BulkUserCreatorToolServlet extends HttpServlet{

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {

        // Create a factory for disk-based file items
        DiskFileItemFactory factory = new DiskFileItemFactory();

        // Configure a repository (to ensure a secure temp location is used)
        ServletContext servletContext = this.getServletConfig().getServletContext();
        File repository = (File) servletContext.getAttribute("javax.servlet.context.tempdir");

        // Create a new file upload handler
        ServletFileUpload upload = new ServletFileUpload(factory);

            //Parse the request to get file items
            List<FileItem> fileItems = upload.parseRequest(request);

            // Process the uploaded items
            Iterator<FileItem> iter = fileItems.iterator();
// file handling

        catch(FileUploadException e){
        catch(Exception e){