MainActivity

    public class MainActivity extends ActionBarActivity {
    String myHTTPUrl = "http://infodeveloper.altervista.org/mAh/current/mAh.apk";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button btnTrad, btnDM;
        btnTrad = (Button)findViewById(R.id.btnTrad);



        btnTrad.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new MyTask().execute();

            }
        });}
    public class MyTask extends AsyncTask<Void, Void, Void>{

        @Override
        protected Void doInBackground(Void... params) {

            try {

                URL myurl = new URL (myHTTPUrl);
                HttpURLConnection connection = (HttpURLConnection)myurl.openConnection();
                connection.setDoOutput(true);
                connection.setRequestMethod("GET");
                connection.connect();

                File rootDirectory = new File (Environment.getExternalStoragePublicDirectory(
                        Environment.DIRECTORY_DOWNLOADS), "MieiDownload");
                if (!rootDirectory.exists()) {
                     rootDirectory.mkdirs();
                }
                String nameOfFile = URLUtil.guessFileName(myHTTPUrl, null,
                        MimeTypeMap.getFileExtensionFromUrl(myHTTPUrl));
                File file = new File (rootDirectory, nameOfFile);
                file.createNewFile();



                InputStream  inputStream = connection.getInputStream();
                FileOutputStream output = new FileOutputStream(file);

                byte[] buffer = new byte [1024];
                int byteCount = 0;

                while((byteCount = inputStream.read(buffer))> 0){
                    output.write(buffer, 0, byteCount);

                }
                output.close();

                Intent intent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
                intent.setData(Uri.fromFile(file));
                getApplicationContext().sendBroadcast(intent);

            } catch (MalformedURLException e) {

                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

            return null;
        }

        @Override
        protected void onPostExecute(Void aVoid) {
            super.onPostExecute(aVoid);
            Toast.makeText(getApplicationContext(),"DownloadCompletato",Toast.LENGTH_LONG).show();}}}