文件下载的问题

Question

我的文件在一台服务器上 我用http方式下载，现在想一点 ”下载“ 就把远程的文件下载本地，下面为什么错误亚
                  response.setContentType(
                           "application/octet-stream;charset=ISO-8859-1");
                   response.setHeader("Content-Disposition",
                                      "attachment;filename=\"" + sl.getFilename().replaceAll("D","F") + "\"");
                   ServletOutputStream out = response.getOutputStream();
                   //FileInputStream in = new FileInputStream(durl);
                   URL u=new URL(durl);
                   HttpURLConnection httpConnection = (HttpURLConnection)u.openConnection();
                   //设置User-Agent
httpConnection.setRequestProperty("User-Agent","NetFox");
//设置断点续传的开始位置
httpConnection.setRequestProperty("RANGE","bytes=2000070");
//获得输入流
InputStream in = httpConnection.getInputStream();                   System.out.println(durl);
                   byte[] b = new byte[1024];
                   int i = 0;
   
                   while ((i = in.read(b)) > 0) {
                       out.write(b, 0, i);
                   }
   
                   out.close();
                   in.close();