java - 应用程序终止或销毁时文件下载不完整

Question

当我从服务器下载文件时，假设我杀死或破坏了应用程序意味着它只会下载一半数据如何在应用程序打开时恢复下载或如何删除文件中不完整的数据。

有什么想法吗？

private void downloadBookDetails(String pMainFolder, String pFileName, String pDownloadURL) {
    Log.i(TAG, "Coming to this downloadBookDetails ");
    try {
        URL url = new URL(pDownloadURL);
        URLConnection ucon = url.openConnection();
        ucon.setReadTimeout(5000);
        ucon.setConnectTimeout(10000);


        InputStream is = ucon.getInputStream();
        BufferedInputStream inStream = new BufferedInputStream(is, 1024 * 5);

        File directory = new File(pMainFolder, pFileName);
        FileOutputStream outStream = new FileOutputStream(directory);
        byte[] buff = new byte[5 * 1024];

        int len;
        while ((len = inStream.read(buff)) != -1) {
            outStream.write(buff, 0, len);
        }


        outStream.flush();
        outStream.close();
        inStream.close();
    } catch (Exception e) {
        //Add Network Error.
        Log.e(TAG, "Download Error Exception " + e.getMessage());

        e.printStackTrace();
    }
}

Answer 1

你应该使用 DownLoad Manager在您的应用程序中下载。这将自动为您处理所有事情。这是一个系统服务，可以处理长时间运行的 HTTP 下载。

更新

如果你想自己下载文件，那么你可以像下面这样使用它:

@SuppressLint("Wakelock")
@Override
protected String doInBackground(String... sUrl) {
    // take CPU lock to prevent CPU from going off if the user 
    // presses the power button during download
    PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
    PowerManager.WakeLock wl = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
         getClass().getName());
    wl.acquire();

    try {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            connection = (HttpURLConnection) url.openConnection();
            File SDCardRoot = Environment.getExternalStorageDirectory();                    
            File file = new File(SDCardRoot,"/"+fileName);
            int downloaded=0;
            if(file.exists()){
                downloaded=(int) file.length();
                connection.setRequestProperty("Range", "bytes=" + (int) file.length() + "-");
            }
            else{
                file.createNewFile();
            }
            connection.setDoInput(true);
            connection.setDoOutput(true);
            connection.connect();

            // expect HTTP 200 OK, so we don't mistakenly save error report 
            // instead of the file


            // this will be useful to display download percentage
            // might be -1: server did not report the length
            int fileLength = connection.getContentLength()+(int)file.length();
            // download the file
            input = connection.getInputStream();      
            if(downloaded>0){
                output = new FileOutputStream(file,true);
            }
            else{
                output = new FileOutputStream(file);
            }
            byte data[] = new byte[1024];
            long total = downloaded;
            int count;
            mProgressDialog.setMax(fileLength/1024);
            while ((count = input.read(data)) != -1) {
                // allow canceling with back button
                if (isCancelled())
                    return null;
                total += count;
                // publishing the progress....
                if (fileLength > 0) // only if total length is known
                    publishProgress((int)total/1024);
                output.write(data, 0, count);
            }
            output.flush();
            if (output != null)
                output.close();
            if (input != null)
                input.close();
            if (connection != null)
                connection.disconnect();
            wl.release();
            return null;
        } catch (Exception e) {
            return e.toString();
        }
    }
    catch (Exception e) {
        return e.toString();
    }        
}