Download file from url in android using retrofit

Downloading files from a url is a common use case these days for a countless number of apps. The files to be downloaded can be of smaller size or bigger size depending on the app requirements. We will be checking how to download a bigger sized file in this tutorial.

We will be using retrofit 2 as our network client in this tutorial.

So first of all, go ahead and add the following dependencies in your newly created android studio project. Be sure that you add the dependencies in your app level build.gradle file and not the project level build.gradle file :

implementation 'com.squareup.retrofit2:retrofit:2.3.0' 

implementation 'com.squareup.okhttp3:okhttp:3.10.0'

Now go to your AndroidManifest.xml file and add the following two permissions inside it

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> 

<uses-permission android:name="android.permission.INTERNET" />

The android.permission.WRITE_EXTERNAL_STORAGE permission is required  to write the downloaded file to android storage whereas the permission android.permission.INTERNET is to make a network call over the internet to fetch the url to download.

First of all create an interface for the network calls which will interact with the network endpoints. See below code :

RetrofitInterface.java

public interface RetrofitInterface {
    @Streaming
    @GET
    Call<ResponseBody> downloadFile(@Url String downloadUrl);
}

In the above code you can notice the @Streaming annotation which will help us to access the raw data which can be processed as streams of data. This data may be bigger than our android's disk space and will help to prevent the data from directly getting downloaded into our device storage. Instead of moving the data directly into the storage we can process the data accordingly and then write to disk accordingly.

If you check here you can see that WRITE_EXTERNAL_STORAGE is listed as a dangerous permission and hence we will need to check runtime permissions for these cases.


So add the following code to your MainActivity.java file

private void askForPermission(String permission, Integer requestCode) {
        if (ContextCompat.checkSelfPermission(MainActivity.this, permission) != PackageManager.PERMISSION_GRANTED) {


            if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, permission)) {
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);

            } else {
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);
            }
        } else if (ContextCompat.checkSelfPermission(MainActivity.this, permission) == PackageManager.PERMISSION_DENIED) {
            Toast.makeText(getApplicationContext(), "Permission was denied", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (ActivityCompat.checkSelfPermission(this, permissions[0]) == PackageManager.PERMISSION_GRANTED) {

            if (requestCode == 101)
                Toast.makeText(this, "Permission granted", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "Permission denied", Toast.LENGTH_SHORT).show();
        }
    }

We have to check for runtime permissions on newer android versions because these newer versions deny permission even if we have added the permission in AndroidManifest.xml file.


Now you will need to create the network call inside MainActivity.java like shown below :

private void downloadFile() {

        OkHttpClient client=new OkHttpClient();
        try {
            client = new OkHttpClient.Builder()
                    .sslSocketFactory(new TLSSocketFactory())
                    .build();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://github.com/")
                .client(client)
                .build();

        RetrofitInterface retrofitInterface = retrofit.create(RetrofitInterface.class);
        Call<ResponseBody> call = retrofitInterface.downloadFile("Navneet7k/ContactsSurf/archive/master.zip");

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, final Response<ResponseBody> response) {
                if (response.isSuccessful()) {

                    Toast.makeText(getApplicationContext(), "Download in progress...", Toast.LENGTH_SHORT).show();
                    downloadFileTask = new DownloadFileTask();
                    downloadFileTask.execute(response.body());

                } else {
                    Toast.makeText(getApplicationContext(), "Oops, something went wrong!!! >> Error : "+response.errorBody(), Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {
                Toast.makeText(getApplicationContext(), "Connection Failure!!!", Toast.LENGTH_SHORT).show();
            }
        });
    }

If you notice here, you can see that i have added an OkHttpClient with TLSSocketFactory() to our retrofit instance. This is because android devices with api level below 20 does not support tls 1.2 by default, we need to enable it by using a custom sslSocketFactory - TLSSocketFactory() like shown below :


TLSSocketFactory.java

public class TLSSocketFactory extends SSLSocketFactory {
    private SSLSocketFactory delegate;

    public TLSSocketFactory() throws KeyManagementException, NoSuchAlgorithmException {
        SSLContext context = SSLContext.getInstance("TLS");
        context.init(null, null, null);
        delegate = context.getSocketFactory();
    }

    @Override
    public String[] getDefaultCipherSuites() {
        return delegate.getDefaultCipherSuites();
    }

    @Override
    public String[] getSupportedCipherSuites() {
        return delegate.getSupportedCipherSuites();
    }

    @Override
    public Socket createSocket() throws IOException {
        return enableTLSOnSocket(delegate.createSocket());
    }

    @Override
    public Socket createSocket(Socket s, String host, int port, boolean autoClose) throws IOException {
        return enableTLSOnSocket(delegate.createSocket(s, host, port, autoClose));
    }

    @Override
    public Socket createSocket(String host, int port) throws IOException, UnknownHostException {
        return enableTLSOnSocket(delegate.createSocket(host, port));
    }

    @Override
    public Socket createSocket(String host, int port, InetAddress localHost, int localPort) throws IOException, UnknownHostException {
        return enableTLSOnSocket(delegate.createSocket(host, port, localHost, localPort));
    }

    @Override
    public Socket createSocket(InetAddress host, int port) throws IOException {
        return enableTLSOnSocket(delegate.createSocket(host, port));
    }

    @Override
    public Socket createSocket(InetAddress address, int port, InetAddress localAddress, int localPort) throws IOException {
        return enableTLSOnSocket(delegate.createSocket(address, port, localAddress, localPort));
    }

    private Socket enableTLSOnSocket(Socket socket) {
        if(socket != null && (socket instanceof SSLSocket)) {
            ((SSLSocket)socket).setEnabledProtocols(new String[] {"TLSv1.2"});
        }
        return socket;
    }
}

as shown above i have added TLSv1.2 to enabled protocols list like this

private Socket enableTLSOnSocket(Socket socket) {
        if(socket != null && (socket instanceof SSLSocket)) {
            ((SSLSocket)socket).setEnabledProtocols(new String[] {"TLSv1.2"});
        }
        return socket;
    }

If you notice the retrofit onResponse callback, you can see DownloadFileTask which is an async task to write the file to the disk , see code below

private class DownloadFileTask extends AsyncTask<ResponseBody, Pair<Integer, Long>, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(ResponseBody... urls) {
            //Copy you logic to calculate progress and call
            saveToDisk(urls[0], "sample-project.zip");
            return null;
        }

        protected void onProgressUpdate(Pair<Integer, Long>... progress) {

            Log.d("API123", progress[0].second + " ");

            if (progress[0].first == 100)
                Toast.makeText(getApplicationContext(), "File downloaded successfully", Toast.LENGTH_SHORT).show();


            if (progress[0].second > 0) {
                int currentProgress = (int) ((double) progress[0].first / (double) progress[0].second * 100);
                progressBar.setProgress(currentProgress);

                txtProgressPercent.setText("Progress " + currentProgress + "%");

            }

            if (progress[0].first == -1) {
                Toast.makeText(getApplicationContext(), "Download failed", Toast.LENGTH_SHORT).show();
            }

        }

        public void doProgress(Pair<Integer, Long> progressDetails) {
            publishProgress(progressDetails);
        }

        @Override
        protected void onPostExecute(String result) {

        }
    }

Also define saveToDisk() where we carry out the file write option mentioned in above async task

private void saveToDisk(ResponseBody body, String filename) {
        try {

            File destinationFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), filename);

            InputStream inputStream = null;
            OutputStream outputStream = null;

            try {

                inputStream = body.byteStream();
                outputStream = new FileOutputStream(destinationFile);
                byte data[] = new byte[4096];
                int count;
                int progress = 0;
                long fileSize = body.contentLength();
                Log.d(TAG, "File Size=" + fileSize);
                while ((count = inputStream.read(data)) != -1) {
                    outputStream.write(data, 0, count);
                    progress += count;
                    Pair<Integer, Long> pairs = new Pair<>(progress, fileSize);
                    downloadFileTask.doProgress(pairs);
                    Log.d(TAG, "Progress: " + progress + "/" + fileSize + " >>>> " + (float) progress / fileSize);
                }

                outputStream.flush();

                Log.d(TAG, destinationFile.getParent());
                Pair<Integer, Long> pairs = new Pair<>(100, 100L);
                downloadFileTask.doProgress(pairs);
                return;
            } catch (IOException e) {
                e.printStackTrace();
                Pair<Integer, Long> pairs = new Pair<>(-1, Long.valueOf(-1));
                downloadFileTask.doProgress(pairs);
                Log.d(TAG, "Failed to save the file!");
                return;
            } finally {
                if (inputStream != null) inputStream.close();
                if (outputStream != null) outputStream.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
            Log.d(TAG, "Failed to save the file!");
            return;
        }
    }

Now edit your activity_main.xml like this

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <TextView
        android:id="@+id/txtProgressPercent"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Downloaded 0%"
        android:textColor="@color/colorAccent"
        android:textStyle="bold"
        android:textAppearance="@style/Base.TextAppearance.AppCompat.Display1"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <ProgressBar
        android:id="@+id/progressBar"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginTop="16dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txtProgressPercent" />

    <Button
        android:id="@+id/button"
        style="@style/ButtonStyle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="DOWNLOAD FILE"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/progressBar" />

</android.support.constraint.ConstraintLayout>

Complete code for your MainActivity.java file will be like the following

public class MainActivity extends AppCompatActivity {

    TextView txtProgressPercent;
    ProgressBar progressBar;
    Button btnDownloadFile;

    DownloadFileTask downloadFileTask;
    private static final String TAG = "MainActivity";


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


        askForPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE, 101);

        txtProgressPercent = findViewById(R.id.txtProgressPercent);
        progressBar = findViewById(R.id.progressBar);
        btnDownloadFile = findViewById(R.id.button);

        btnDownloadFile.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                downloadFile();
            }
        });
    }

    private void downloadFile() {

        OkHttpClient client = new OkHttpClient();
        try {
            client = new OkHttpClient.Builder()
                    .sslSocketFactory(new TLSSocketFactory())
                    .build();
        } catch (KeyManagementException e) {
            e.printStackTrace();
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("https://github.com/")
                .client(client)
                .build();

        RetrofitInterface retrofitInterface = retrofit.create(RetrofitInterface.class);
        Call<ResponseBody> call = retrofitInterface.downloadFile("Navneet7k/ContactsSurf/archive/master.zip");

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Call<ResponseBody> call, final Response<ResponseBody> response) {
                if (response.isSuccessful()) {

                    Toast.makeText(getApplicationContext(), "Download in progress...", Toast.LENGTH_SHORT).show();
                    downloadFileTask = new DownloadFileTask();
                    downloadFileTask.execute(response.body());

                } else {
                    Toast.makeText(getApplicationContext(), "Oops, something went wrong!!! >> Error : " + response.errorBody(), Toast.LENGTH_SHORT).show();
                }
            }

            @Override
            public void onFailure(Call<ResponseBody> call, Throwable t) {
                Toast.makeText(getApplicationContext(), "Connection Failure!!!", Toast.LENGTH_SHORT).show();
            }
        });
    }


    private class DownloadFileTask extends AsyncTask<ResponseBody, Pair<Integer, Long>, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

        }

        @Override
        protected String doInBackground(ResponseBody... urls) {
            //Copy you logic to calculate progress and call
            saveToDisk(urls[0], "sample-project.zip");
            return null;
        }

        protected void onProgressUpdate(Pair<Integer, Long>... progress) {

            Log.d("API123", progress[0].second + " ");

            if (progress[0].first == 100)
                Toast.makeText(getApplicationContext(), "File downloaded successfully", Toast.LENGTH_SHORT).show();


            if (progress[0].second > 0) {
                int currentProgress = (int) ((double) progress[0].first / (double) progress[0].second * 100);
                progressBar.setProgress(currentProgress);

                txtProgressPercent.setText("Progress " + currentProgress + "%");

            }

            if (progress[0].first == -1) {
                Toast.makeText(getApplicationContext(), "Download failed", Toast.LENGTH_SHORT).show();
            }

        }

        public void doProgress(Pair<Integer, Long> progressDetails) {
            publishProgress(progressDetails);
        }

        @Override
        protected void onPostExecute(String result) {

        }
    }

    private void saveToDisk(ResponseBody body, String filename) {
        try {

            File destinationFile = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS), filename);

            InputStream inputStream = null;
            OutputStream outputStream = null;

            try {

                inputStream = body.byteStream();
                outputStream = new FileOutputStream(destinationFile);
                byte data[] = new byte[4096];
                int count;
                int progress = 0;
                long fileSize = body.contentLength();
                Log.d(TAG, "File Size=" + fileSize);
                while ((count = inputStream.read(data)) != -1) {
                    outputStream.write(data, 0, count);
                    progress += count;
                    Pair<Integer, Long> pairs = new Pair<>(progress, fileSize);
                    downloadFileTask.doProgress(pairs);
                    Log.d(TAG, "Progress: " + progress + "/" + fileSize + " >>>> " + (float) progress / fileSize);
                }

                outputStream.flush();

                Log.d(TAG, destinationFile.getParent());
                Pair<Integer, Long> pairs = new Pair<>(100, 100L);
                downloadFileTask.doProgress(pairs);
                return;
            } catch (IOException e) {
                e.printStackTrace();
                Pair<Integer, Long> pairs = new Pair<>(-1, Long.valueOf(-1));
                downloadFileTask.doProgress(pairs);
                Log.d(TAG, "Failed to save the file!");
                return;
            } finally {
                if (inputStream != null) inputStream.close();
                if (outputStream != null) outputStream.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
            Log.d(TAG, "Failed to save the file!");
            return;
        }
    }

    private void askForPermission(String permission, Integer requestCode) {
        if (ContextCompat.checkSelfPermission(MainActivity.this, permission) != PackageManager.PERMISSION_GRANTED) {


            if (ActivityCompat.shouldShowRequestPermissionRationale(MainActivity.this, permission)) {
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);

            } else {
                ActivityCompat.requestPermissions(MainActivity.this, new String[]{permission}, requestCode);
            }
        } else if (ContextCompat.checkSelfPermission(MainActivity.this, permission) == PackageManager.PERMISSION_DENIED) {
            Toast.makeText(getApplicationContext(), "Permission was denied", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    public void onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (ActivityCompat.checkSelfPermission(this, permissions[0]) == PackageManager.PERMISSION_GRANTED) {

            if (requestCode == 101)
                Toast.makeText(this, "Permission granted", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "Permission denied", Toast.LENGTH_SHORT).show();
        }
    }
}