Android断点续传学习

先学习断点续传热热身，为多线程下载预热；

其实重点就是下载这里；

1，下载范围的设定

 urlConnection.setRequestProperty("Range","bytes=" + start + "-" + info.getLength());  

2 , 文件移动到指定位置

randomFile.seek(start); 

其他的没有难度，很简单；可以使用数据库或者文件作为缓存文件

主要是一个思路；这里简单的记录一下；作为学习记录

    class MyThread extends Thread{
         private FileInfo info = null;
         public MyThread(FileInfo threadInfo) {
             this.info = threadInfo;
         }
         @Override
         public void run() {
             //向数据库添加线程信息
             if(!threadDAO.isExits(info.getUrl())){
                 threadDAO.insert(info);
             }
             HttpURLConnection urlConnection = null;
             RandomAccessFile randomFile =null;
             InputStream inputStream = null;
             try {
                 URL url = new URL(info.getUrl());
                 urlConnection = (HttpURLConnection) url.openConnection();
                 urlConnection.setConnectTimeout(3000);
                 urlConnection.setRequestMethod("GET");
                 //设置下载位置
                 int start = info.getStart() + info.getNow();
                 urlConnection.setRequestProperty("Range","bytes=" + start + "-" + info.getLength());

                 //设置文件写入位置
                 File file = new File(DOWNLOAD_PATH,FILE_NAME);
                 randomFile = new RandomAccessFile(file, "rwd");
                 randomFile.seek(start);

                 //向Activity发广播
                 Intent intent = new Intent(ACTION_UPDATE);
                 finished += info.getNow();

                 if (urlConnection.getResponseCode() == HttpStatus.SC_PARTIAL_CONTENT) {
                     //获得文件流
                     inputStream = urlConnection.getInputStream();
                     byte[] buffer = new byte[512];
                     int len = -1;
                     long time = System.currentTimeMillis();
                     while ((len = inputStream.read(buffer))!= -1){
                         //写入文件
                         randomFile.write(buffer,0,len);
                         //把进度发送给Activity
                         finished += len;
                         //看时间间隔，时间间隔大于500ms再发
                         if(System.currentTimeMillis() - time >500){
                             time = System.currentTimeMillis();
                             intent.putExtra("now",finished *100 /fileInfo.getLength());
                             context.sendBroadcast(intent);
                         }
                         //判断是否是暂停状态
                         if(isPause){
                             threadDAO.update(info.getUrl(),finished);
                             return; //结束循环
                         }
                     }
                     //删除线程信息
                     threadDAO.delete(info.getUrl());
                 }
             }catch (Exception e){
                 e.printStackTrace();
             }finally {//回收工作略
             }
         }
     }
 }