Working of Progress Bar for a File Download

0 votes

Here is the issue I am facing:-

I am trying to write a simple application that gets updated. For this I need a simple function that can download a file and show the current progress in a ProgressDialog. I know how to do the ProgressDialog, but I'm not sure how to display the current progress and how to download the file in the first place.

Jun 26, 2018 in Java by developer_1
• 3,280 points
658 views

1 answer to this question.

0 votes

Once of the ways to achieve is this:-

Using AsyncTask and show the download progress in a dialog

This method will allow you to execute some background processes and update the UI at the same time (in this case, we'll update a progress bar).

This is an example code:

// declare the dialog as a member field of your activity
ProgressDialog mProgressDialog;

// instantiate it within the onCreate method
mProgressDialog = new ProgressDialog(YourActivity.this);
mProgressDialog.setMessage("A message");
mProgressDialog.setIndeterminate(true);
mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
mProgressDialog.setCancelable(true);

// execute this when the downloader must be fired
final DownloadTask downloadTask = new DownloadTask(YourActivity.this);
downloadTask.execute("the url to the file you want to download");

mProgressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
    @Override
    public void onCancel(DialogInterface dialog) {
        downloadTask.cancel(true);
    }
});

The AsyncTask will look like this:

// 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;
    private PowerManager.WakeLock mWakeLock;

    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;
                // publishing the progress....
                if (fileLength > 0) // only if total length is known
                    publishProgress((int) (total * 100 / fileLength));
                output.write(data, 0, 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;
    }

The method above (doInBackground) runs always on a background thread. You shouldn't do any UI tasks there. On the other hand, the onProgressUpdate and onPreExecute run on the UI thread, so there you can change the progress bar:

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        // 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);
        mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
             getClass().getName());
        mWakeLock.acquire();
        mProgressDialog.show();
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        // if we get here, length is known, now set indeterminate to false
        mProgressDialog.setIndeterminate(false);
        mProgressDialog.setMax(100);
        mProgressDialog.setProgress(progress[0]);
    }

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

For this to run, you need the WAKE_LOCK permission.

<uses-permission android:name="android.permission.WAKE_LOCK" />
answered Jun 26, 2018 by Rishabh
• 3,540 points

Related Questions In Java

0 votes
1 answer

Retrieving the path of a running jar file

Its quite simple. Try using the below ...READ MORE

answered May 25, 2018 in Java by geek.erkami
• 2,320 points
752 views
0 votes
1 answer

Number of lines in a file in Java

I found this an efficient way in counting ...READ MORE

answered Jul 3, 2018 in Java by scarlett
• 1,280 points
18 views
0 votes
1 answer

How to download a file from spring controllers?

@RequestMapping(value = "/files/{file_name}", method = RequestMethod.GET) public void ...READ MORE

answered Sep 4, 2018 in Java by code.reaper12
• 3,450 points
93 views
0 votes
1 answer

Should a class file always be inside package for importing it in jsp page?

Hey there! It is not necessary for the ...READ MORE

answered May 24 in Java by Karan
20 views
0 votes
1 answer

Fixing android.os.NetworkOnMainThreadException in Java

Android has some good tips on good ...READ MORE

answered Jun 12, 2018 in Java by Rishabh
• 3,540 points
1,199 views
0 votes
1 answer

How to pass an object from one activity to another on Android

One option could be letting your custom ...READ MORE

answered Jun 25, 2018 in Java by Rishabh
• 3,540 points
339 views
0 votes
1 answer

Calling SOAP web services on Android using JAVA

Android does not provide any sort of ...READ MORE

answered Jun 28, 2018 in Java by Sushmita
• 6,840 points
73 views
0 votes
1 answer

How to configure Android SDK for finding JDK

Actual SETUP: OS: Windows 8.1 JDK file: jdk-8u11-windows-x64.exe ADT file: ...READ MORE

answered Jun 29, 2018 in Java by Rishabh
• 3,540 points
32 views
0 votes
1 answer

How do I create a Java string from the contents of a file?

If you're looking for an alternative that ...READ MORE

answered Apr 19, 2018 in Java by Rishabh
• 3,540 points
72 views
0 votes
1 answer

How to download and save a file from Internet using Java?

public void saveUrl(final String filename, final String ...READ MORE

answered May 24, 2018 in Java by Rishabh
• 3,540 points
32 views