Question

protected void doDownload(final String urlLink, final String fileName) {
       Thread dx = new Thread() {

                 public void run() {

                 File root = android.os.Environment.getExternalStorageDirectory();              
                 File dir = new File (root.getAbsolutePath() + "/Content2/");
                 if(dir.exists()==false) {

                         dir.mkdirs();
                    }
              //Save the path as a string value

               try 
               {
                       URL url = new URL(urlLink);
                       Log.i("FILE_NAME", "File name is "+imageFile);
                       Log.i("FILE_URLLINK", "File URL is "+url);
                       URLConnection connection = url.openConnection();
                       connection.connect();
                       // this will be useful so that you can show a typical 0-100% progress bar
                       int fileLength = connection.getContentLength();

                       // download the file
                       InputStream input = new BufferedInputStream(url.openStream());
                       OutputStream output = new FileOutputStream(dir+"/"+imageFile);

                       byte data[] = new byte[1024];
                       long total = 0;
                       int count;
                       while ((count = input.read(data)) != -1) {
                           total += count;

                           output.write(data, 0, count);
                       }

                       output.flush();
                       output.close();
                       input.close();
                   } 
               catch (Exception e) 
               {
                    e.printStackTrace();
                    Log.i("ERROR ON DOWNLOADING FILES", "ERROR IS" +e);
                   }
           }
       };

       dx.start();      
   }

通过这个，我无法从服务器下载文件。

如何解决这个问题？

Answer 1

首先，您应该使用 Async-Task。

以下是如何做到这一点

final DownloadTask downloadTask = new DownloadTask(YourActivity.this);
downloadTask.execute("the url to the file you want to download");

// usually, subclasses of AsyncTask are declared inside the activity class.
// that way, you can easily modify the UI thread from here
private class DownloadTask extends AsyncTask<String, Integer, String> {

    private Context context;

    public DownloadTask(Context context) {
        this.context = context;
    }

    @Override
    protected String doInBackground(String... sUrl) {
        InputStream input = null;
        OutputStream output = null;
        HttpURLConnection connection = null;
        try {
            URL url = new URL(sUrl[0]);
            connection = (HttpURLConnection) url.openConnection();
            connection.connect();

            // expect HTTP 200 OK, so we don't mistakenly save error report
            // instead of the file
            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                return "Server returned HTTP " + connection.getResponseCode()
                        + " " + connection.getResponseMessage();
            }

            // this will be useful to display download percentage
            // might be -1: server did not report the length
            int fileLength = connection.getContentLength();

            // download the file
            input = connection.getInputStream();
            output = new FileOutputStream("/sdcard/file_name.extension");

            byte data[] = new byte[4096];
            long total = 0;
            int count;
            while ((count = input.read(data)) != -1) {
                // allow canceling with back button
                if (isCancelled()) {
                    input.close();
                    return null;
                }
                total += count;
            }
        } catch (Exception e) {
            return e.toString();
        } finally {
            try {
                if (output != null)
                    output.close();
                if (input != null)
                    input.close();
            } catch (IOException ignored) {
            }

            if (connection != null)
                connection.disconnect();
        }
        return null;
    }

@Override
    protected void onPostExecute(String result) {
        if (result != null)
            Toast.makeText(context,"Download error: "+result, Toast.LENGTH_LONG).show();
        else
            Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show();
    }

如何从Android服务器下载sqlite数据库文件？

1 个答案: