How to upload File from form data POST in Android with Retrofit 2

 The last day I explain how to upload a simple CSV file using node. And now I teach how to upload from android device.

Get source code here:  GitHub

This article is write in java... later I'll add the method for kotlin. The logic is not changed, only the format code.

1) Is necessary add the dependencies in gradle: module

implementation 'com.google.code.gson:gson:2.8.6'
// RETROFIT //
implementation 'com.squareup.retrofit2:retrofit:2.6.2'
implementation 'com.squareup.retrofit2:converter-gson:2.6.2'
implementation 'com.squareup.retrofit2:converter-scalars:2.5.0'

2) Add permissions in AndroidManifest.xml and modified the application for work with network security policy

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


in applitacion add this for work with HTTP
android:usesCleartextTraffic="true"

3) Add all code necessary for request any permission for write or read the memory card (you can use the traditional system for request permission or use contract). I worked directly in MainActivity and added a button to test my app

private final int PERMISSION = 100;
private final String[] permissions = {
	Manifest.permission.WRITE_EXTERNAL_STORAGE,
	Manifest.permission.READ_EXTERNAL_STORAGE
};
private Button btn;
private ProgressBar progressBar;

@Override
protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_main);
	btn = (Button) findViewById(R.id.button);
	progressBar = (ProgressBar) findViewById(R.id.progressBar);
	progressBar.setVisibility(View.GONE);
	verificPermission();
}

public void send(View v) {
	btn.setEnabled(false);
	progressBar.setVisibility(View.VISIBLE);
	initialize(); // in this point, this method is not exist
}

private void verificPermission() {
	if(ContextCompat.checkSelfPermission(this, Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_DENIED) {
		showPermissionRequest();
	}
}

private void showPermissionRequest() {
	AlertDialog.Builder builder = new AlertDialog.Builder(this);
	builder.setTitle("Information");
	builder.setMessage("Next, a dialog box will be shown where you will be asked to authorize the media handling permissions, please accept them so that the application can continue working properly ...");
	builder.setPositiveButton("Ok", new DialogInterface.OnClickListener() {
		@Override
		public void onClick(DialogInterface dialog, int which) {
			getPermissions();
		}
	});
	builder.setCancelable(false);
	builder.show();
}

private void getPermissions() {
	ActivityCompat.requestPermissions(this, permissions, PERMISSION);
}

@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
	super.onRequestPermissionsResult(requestCode, permissions, grantResults);
	if(requestCode == PERMISSION) {
		showMessage("permissions granted");
	}
}

private void showMessage(String message) {
	message = (message.isEmpty()) ? "There is no message to show" : message;
	Toast.makeText(this, message, Toast.LENGTH_LONG).show();
}

4) Create a class singlenton for retrofit Instance

public class RetrofitInstance {
    private static Retrofit retrofit;
    private static final String BASE_URL = "http://192.168.0.160:3000"; // this IP is changed for your IP

    public static Retrofit getInstance() {
        final OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .connectTimeout(1, TimeUnit.MINUTES)
                .writeTimeout(1,TimeUnit.MINUTES)
                .readTimeout(1,TimeUnit.MINUTES)
                .build();
        if (retrofit==null) {
            retrofit = new Retrofit.Builder()
                .client(okHttpClient)
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        }
        return retrofit;
    }
}

5) Create a interface for upload the file from form data (multipart) POST

public interface RetrofitServices {

    @Multipart
    @POST("upload/")
    Call<CSVUploadResponse> uploadAttachment(@Part MultipartBody.Part filePart);

}

6) Create a simple class for read the response message (change this class is not using my project node for upload file

public class CSVUploadResponse {

    @SerializedName("message")
    private String message;

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

7) Implements these method in MainActivity, I created a ExportCSVFaker for generate a simple file for upload (this code is in GitHub)

private void initialize() {
	ExportCSVFaker exportCSVFaker = new ExportCSVFaker(this);
	if(exportCSVFaker.isCSVExist()) {
		sendCSVToServer(exportCSVFaker.getCsv());
	} else {
		showMessage("The file was not generated");
	}
}

private void sendCSVToServer(File csv) {
	MultipartBody.Part filePart = MultipartBody.Part.createFormData(
			"uploadFile",
			csv.getName(),
			RequestBody.create(MediaType.parse("text/plain" + "; charset=utf-8"), csv)
	);
	RetrofitServices retroServices = RetrofitInstance.getInstance().create(RetrofitServices.class);
	Call<CSVUploadResponse> responseCall = retroServices.uploadAttachment(filePart);

	responseCall.enqueue(new Callback<CSVUploadResponse>() {
		@Override
		public void onResponse(Call<CSVUploadResponse> call, Response<CSVUploadResponse> response) {
			showMessage(response.message());
			setVisibilityElements();
		}

		@Override
		public void onFailure(Call<CSVUploadResponse> call, Throwable t) {
			t.printStackTrace();
			showMessage("The upload is failed");
			setVisibilityElements();
		}
	});
}

private void setVisibilityElements() {
	btn.setEnabled(true);
	progressBar.setVisibility(View.GONE);
}

The magic is in the method "sendCSVToServer" and the parameter of type File for send to server using the class "MultipartBody.Part" for add to "responseCall"

The result is the next

That's folks