在Android ---服务器重启后如何恢复下载？

Question

任何人帮助我.. 我的问题是，当我下载文件时，有时服务器被弯曲＆amp;服务器启动后，我只需要下载50％我需要从51％下载。因为在服务器停止之前完成了50％的下载。

我的代码在下面..但是它不起作用。

 HttpURLConnection connection = (HttpURLConnection) url.openConnection();
if(ISSUE_DOWNLOAD_STATUS.intValue()==ECMConstant.ECM_DOWNLOADING){
    File file=new File(DESTINATION_PATH);
    if(file.exists()){
         downloaded = (int) file.length();
         connection.setRequestProperty("Range", "bytes="+(file.length())+"-");
    }
}else{
    connection.setRequestProperty("Range", "bytes=" + downloaded + "-");
}
connection.setDoInput(true);
connection.setDoOutput(true);
progressBar.setMax(connection.getContentLength());
 in = new BufferedInputStream(connection.getInputStream());
 fos=(downloaded==0)? new FileOutputStream(DESTINATION_PATH): new FileOutputStream(DESTINATION_PATH,true);
 bout = new BufferedOutputStream(fos, 1024);
byte[] data = new byte[1024];
int x = 0;
while ((x = in.read(data, 0, 1024)) >= 0) {
    bout.write(data, 0, x);
     downloaded += x;
     progressBar.setProgress(downloaded);
}

感谢。