jspSmartUpload下载错误

package com.file.downloading;

import java.io.*;
import java.net.*;
import javax.servlet.*;
import javax.servlet.http.*;
import com.jspsmart.upload.SmartUpload;

public class DownloadFile extends HttpServlet {
  private ServletConfig config;

  public final void init(ServletConfig config) {
    this.config = config;
  }

  protected void processRequest(HttpServletRequest request,
    HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();

    try {
SmartUpload su = new SmartUpload();
System.out.println("this.config is null : "
          + (null == this.config));
su.initialize(this.config, request, response);
su.setContentDisposition(null);
su.downloadFile("newfile.txt");
    } catch (Exception ex) {
      System.out.println(this.getClass().getName() + " error "
        + ex.toString());
    } finally {
      out.close();
    }
}

  protected void doGet(HttpServletRequest request,
    HttpServletResponse response) throws ServletException, IOException {
      processRequest(request, response);
  }

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

  public String getServletInfo() {
    return "Short description";
  }
}

这段代码可以执行，文件也可以下载，但是下载后的文件内容为空，请教?!
这段代码可以执行，文件也可以下载，但是下载后的文件内容为空，请教?!
这段代码可以执行，文件也可以下载，但是下载后的文件内容为空，请教?!