pausing download to add garbage to file then resuming - android

Question

I wish to pause the file download at a particular point and add some bytes of data to it and then resume the download. How do I do it?

Below is a code snippet showing what I am downloading :-

private void startDownload() {
        String url = "http://coderzheaven.com/sample_folder/sample_file.png";
        new DownloadFileAsync().execute(url);
    }

Now, below is the DownloadFileAsync class

class DownloadFileAsync extends AsyncTask<String, String, String> {

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        showDialog(DIALOG_DOWNLOAD_PROGRESS);
    }

    @Override
    protected String doInBackground(String... aurl) {
        int count;

        try {

            URL url = new URL(aurl[0]);
            URLConnection conexion = url.openConnection();
            conexion.connect();

            int lenghtOfFile = conexion.getContentLength();
            Log.d("ANDRO_ASYNC", "Length of file: " + lenghtOfFile);

            InputStream input = new BufferedInputStream(url.openStream());

            File SDCardRoot = Environment.getExternalStorageDirectory();
            //create a new file, to save the downloaded file
            File file = new File(SDCardRoot,"downloaded_file.png");

            OutputStream output = new FileOutputStream(file);

            byte data[] = new byte[1024];

            long total = 0;

            while ((count = input.read(data)) != -1) {
                total += count;
                publishProgress("" + (int) ((total * 100) / lenghtOfFile));
                output.write(data, 0, count);
            }

            output.flush();
            output.close();
            input.close();
        } catch (Exception e) {
        }
        return null;

    }

    protected void onProgressUpdate(String... progress) {
        Log.d("ANDRO_ASYNC", progress[0]);
        mProgressDialog.setProgress(Integer.parseInt(progress[0]));
    }

    @Override
    protected void onPostExecute(String unused) {
        dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
    }
}

Answer 1

connection.setRequestProperty("Range", "bytes=" + ***downloaded*** + "-");

Make "downloaded" as global variable, because download start from this position.

when you press on restart button, check value of this downloaded variable,must not zero all time.

Please change the things in below code

public class DownloadWithProgressActivity extends Activity {

    public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
    private Button startBtn, pauseButton, resumeButton;
    private ProgressBar bar;
    URLConnection conexion;
    OutputStream output;
    static int count = 0;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        startBtn = (Button) findViewById(R.id.startBtn);
        pauseButton = (Button) findViewById(R.id.button1);
        resumeButton = (Button) findViewById(R.id.button2);
        bar = (ProgressBar) findViewById(R.id.progressBar1);
        bar.setVisibility(ProgressBar.INVISIBLE);
        bar.setId(0);

        startBtn.setOnClickListener(new OnClickListener() {
            public void onClick(View v) {
                startDownload();
            }
        });
        pauseButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                try {
                    output.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        resumeButton.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {
                //  not getting what to write here
            }
        });
    }

    private void startDownload() {
        String url = "http://farm1.static.flickr.com/114/298125983_0e4bf66782_b.jpg";
        new DownloadFileAsync().execute(url);
    }

    class DownloadFileAsync extends AsyncTask<String, String, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            bar.setVisibility(ProgressBar.VISIBLE);

        }

        @Override
        protected String doInBackground(String... aurl) {
            int downloaded = 0;
            File file = new File("/sdcard/some_photo_from_gdansk_poland.jpg");
            URL url = null;
            try {
                url = new URL(aurl[0]);
            } catch (MalformedURLException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            try {
                conexion = url.openConnection();
                if (file.exists()) {
                    downloaded = (int) file.length();
                    conexion.setRequestProperty("Range", "bytes="+(file.length())+"-");

                }

                else {
                    conexion.setRequestProperty("Range", "bytes=" + downloaded
                            + "-");
                }
            } catch (Exception exception1) {
            }
            conexion.setDoInput(true);
            conexion.setDoOutput(true);

            System.out.println(tryGetFileSize(url));
            conexion.setRequestProperty("Range", "bytes=" + count + "-");
            try {
                conexion.connect();
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            int lenghtOfFile = conexion.getContentLength();
            Log.d("ANDRO_ASYNC", "Lenght of file: " + lenghtOfFile);
            InputStream input = null;
            try {
                input = new BufferedInputStream(url.openStream());
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            try {
                output = new FileOutputStream(file);
            } catch (FileNotFoundException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            byte data[] = new byte[1024];
            long total = 0;
            try {
                while ((count = input.read(data)) != -1) {
                    total += count;
                    publishProgress("" + (int) ((total * 100) / lenghtOfFile));
                    output.write(data, 0, count);
                }
            } catch (IOException e1) {
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }
            try {
                output.flush();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            try {
                output.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            try {
                input.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            return null;

        }

        protected void onProgressUpdate(String... progress) {
            Log.d("ANDRO_ASYNC", progress[0]);
            bar.setProgress(Integer.parseInt(progress[0]));
            System.out.println(Integer.parseInt(progress[0]));
        }

        protected void onPostExecute(String unused) {
        }

        int tryGetFileSize(URL url) {
            HttpURLConnection conn = null;
            try {
                conn = (HttpURLConnection) url.openConnection();
                conn.setRequestMethod("HEAD");
                conn.getInputStream();
                return conn.getContentLength();
            } catch (IOException e) {
                return -1;
            } finally {
                conn.disconnect();
            }
        }

    }
}