断点续传

HTTP文件断点续传原理解析，欢迎star或fork

流程图

核心原理

  HttpURLConnection connection;
        RandomAccessFile raf;
        InputStream is;
        try {
            URL url = new URL(downloadInfo.getUrl());
            connection = (HttpURLConnection) url.openConnection();
            connection.setConnectTimeout(3000);
            connection.setRequestMethod("GET");
            //设置下载位置
            long start = downloadInfo.getStart() + downloadInfo.getProgress();
            connection.setRequestProperty("Range", "bytes=" + start + "-" + downloadInfo.getEnd());

            //设置文件写入位置
            File file = new File(DownloadService.DOWNLOAD_PATH, mFileInfo.getFileName());
            raf = new RandomAccessFile(file, "rwd");
            raf.seek(start);

            progress += downloadInfo.getProgress();
            Log.e(TAG,"下载文件进度(size)："+ downloadInfo.getProgress() + "");
            Log.e(TAG,"HttpResponseCode ==="+connection.getResponseCode() + "");
            //开始下载
            if (connection.getResponseCode() == HttpURLConnection.HTTP_PARTIAL) {
                Log.e(TAG,"剩余文件(size):"+connection.getContentLength() + "");
                Intent intent = new Intent(DownloadService.ACTION_UPDATE);//广播intent
                is = connection.getInputStream();
                byte[] buffer = new byte[1024 * 4];
                int len = -1;
                long time = System.currentTimeMillis();
                while ((len = is.read(buffer)) != -1) {
                    //下载暂停时，保存进度
                    if (isPause) {
                        Log.e(TAG,"保存进度文件(size):"+progress + "");
                        mDatabaseOperation.update(mFileInfo.getUrl(), mFileInfo.getId(), progress);
                        return;
                    }
                    //写入文件
                    raf.write(buffer, 0, len);
                    //把下载进度发送广播给Activity
                    progress += len;
                    if (System.currentTimeMillis() - time > 1000) {//超过一秒，就刷新UI
                        time = System.currentTimeMillis();
                        sendBroadcast(intent,(int)(progress * 100 / mFileInfo.getLength()));
                        Log.e(TAG,"进度：" + progress * 100 / mFileInfo.getLength() + "%");
                    }
                }
                sendBroadcast(intent,100);
                /**
                 *  删除下载信息（重新下载）
                 */
                mDatabaseOperation.delete(mFileInfo.getUrl(), mFileInfo.getId());
                is.close();
            }
            raf.close();
            connection.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }

Demo演示