Downloading a File to Device

[Andy Crowther]

So thanks to help yesterday, I can now parse the xml file I need.  Today I would like to be able to download this file through the app, so it can then be parsed.

I've got what looks to be the code I need.  It doesn't throw any errors at least and looks like this -

import android.util.Log;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

/**
 * A utility that downloads a file from a URL.
 *
 * @author www.codejava.net
 */
public class DownloadFromURL {
    private static final int BUFFER_SIZE = 4096;

    /**
     * Downloads a file from a URL
     *
     * @param fileURL HTTP URL of the file to be downloaded
     * @param saveDir path of the directory to save the file
     * @throws IOException
     */
    public static void downloadFile(String fileURL, String saveDir)
            throws IOException {
        URL url = new URL(fileURL);
        HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
        int responseCode = httpConn.getResponseCode();

        // always check HTTP response code first
        if (responseCode == HttpURLConnection.HTTP_OK) {
            String fileName = "";
            String disposition = httpConn.getHeaderField("Content-Disposition");
            String contentType = httpConn.getContentType();
            int contentLength = httpConn.getContentLength();

            if (disposition != null) {
                // extracts file name from header field
                int index = disposition.indexOf("filename=");
                if (index > 0) {
                    fileName = disposition.substring(index + 10,
                            disposition.length() - 1);
                }
            } else {
                // extracts file name from URL
                fileName = fileURL.substring(fileURL.lastIndexOf("/") + 1,
                        fileURL.length());
            }

            // opens input stream from the HTTP connection
            InputStream inputStream = httpConn.getInputStream();
            String saveFilePath = saveDir + File.separator + fileName;

            // opens an output stream to save into file
            FileOutputStream outputStream = new FileOutputStream(saveFilePath);

            int bytesRead = -1;
            byte[] buffer = new byte[BUFFER_SIZE];
            while ((bytesRead = inputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }

            outputStream.close();
            inputStream.close();

            Log.i("Download","File downloaded");
        } else {
            Log.i("Download","No file to download. Server replied HTTP code: " + responseCode);
        }
        httpConn.disconnect();
    }
}

It is then called by this code -

String fileURL = "http://m.highways.gov.uk/feeds/rss/AllEvents.xml";
            String saveDir = "raw";
            try {
                DownloadFromURL.downloadFile(fileURL, saveDir);
            } catch (IOException ex) {
                ex.printStackTrace();
            }

The problem is, it does flag a runtime error as clearly I need to extend AsyncTask.  I've tried to do this, but can't seem to get the code right.  How should it look?

Thanks for the help!

[Tim Moores]

Network access should always be done in the background on Android, so as not too block the main thread for an indeterminate amount of time. AsyncTask is one way to do this, but you can also start a thread something like this:

new Thread(new Runnable() {
    public void run() {
        // network access here
    }
}).start();

Or use Android's DownloadManager to handle it for you: https://www.sandersdenardi.com/using-the-android-downloadmanager/

[Andy Crowther]

Thanks, I feel like I'm getting there, but back to the file not found issues I had with parsing.  My code is now -

public class DownloadFromURL implements Runnable {
    private static final int BUFFER_SIZE = 4096;

    @Override
    public void run() {
        Log.i("Download From URL", "Run");

        String fileURL = "http://m.highways.gov.uk/feeds/rss/AllEvents.xml";
        String saveDir = "/data/data/com.androidandyuk.bikersbestfriend/files";
        URL url;
        try {
            url = new URL(fileURL);

            HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();

            int responseCode = httpConn.getResponseCode();
            Log.i("Download from URL", "Resp Code :" + responseCode);
            // always check HTTP response code first
            if (responseCode == HttpURLConnection.HTTP_OK) {
                String fileName = "";
                String disposition = httpConn.getHeaderField("Content-Disposition");
                String contentType = httpConn.getContentType();
                int contentLength = httpConn.getContentLength();

                if (disposition != null) {
                    // extracts file name from header field
                    int index = disposition.indexOf("filename=");
                    if (index > 0) {
                        fileName = disposition.substring(index + 10,
                                disposition.length() - 1);
                    }
                } else {
                    // extracts file name from URL
                    fileName = fileURL.substring(fileURL.lastIndexOf("/") + 1,
                            fileURL.length());
                }

                // opens input stream from the HTTP connection
                InputStream inputStream = httpConn.getInputStream();
                String saveFilePath = saveDir + File.separator + fileName;
                Log.i("Download from URL", "Opening a Stream");
                // opens an output stream to save into file
                FileOutputStream outputStream = new FileOutputStream(saveFilePath);  // this line causes the error
                int bytesRead = -1;
                byte[] buffer = new byte[BUFFER_SIZE];
                while ((bytesRead = inputStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, bytesRead);
                }

                outputStream.close();
                inputStream.close();

                Log.i("Download", "File downloaded");
            } else {
                Log.i("Download", "No file to download. Server replied HTTP code: " + responseCode);
            }

            httpConn.disconnect();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

And called by -

DownloadFromURL getTraffic = new DownloadFromURL();
            Thread t = new Thread(getTraffic);
            t.start();

But I get the error pointing at the FileOutputStream -

W/System.err: java.io.FileNotFoundException: /data/data/com.androidandyuk.bikersbestfriend/files/AllEvents.xml (No such file or directory)
05-18 10:34:50.286 15549-15800/com.androidandyuk.bikersbestfriend.live W/System.err:     at java.io.FileOutputStream.open(Native Method)
05-18 10:34:50.286 15549-15800/com.androidandyuk.bikersbestfriend.live W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:221)
05-18 10:34:50.286 15549-15800/com.androidandyuk.bikersbestfriend.live W/System.err:     at java.io.FileOutputStream.<init>(FileOutputStream.java:108)
05-18 10:34:50.286 15549-15800/com.androidandyuk.bikersbestfriend.live W/System.err:     at com.androidandyuk.bikersbestfriend.DownloadFromURL.run(DownloadFromURL.java:61)
05-18 10:34:50.286 15549-15800/com.androidandyuk.bikersbestfriend.live W/System.err:     at java.lang.Thread.run(Thread.java:761)

I understand I can't save to raw, hence the data/data/... saveDir.

Any ideas?

[Dave Tolls]

Does that directory exist?
The OutputStream won't create it.

[Dave Tolls]

Personally, I would use the tools available.
As Tim says, there's a DownloadManager built into Android.

[Tim Moores]

Don't try to construct absolute paths on an Android device. See https://developer.android.com/guide/topics/data/data-storage.html#filesInternal for how to read and write files.

[Andy Crowther]

Hi guys, just posting to say thanks for the help.  I did some research on DownloadManager and currently I'm downloading the xml to the Downloads folder and parsing it from there.  Perhaps at somepoint I'll look into parsing it direct from the http source, but for now it works at least!