Upload multiple file using Retrofit as multipart

private void mulipleFileUploadFile(Uri[] fileUri) {
    OkHttpClient okHttpClient = new OkHttpClient();
    OkHttpClient clientWith30sTimeout = okHttpClient.newBuilder()
            .readTimeout(30, TimeUnit.SECONDS)
            .build();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(API_URL_BASE)
            .addConverterFactory(new MultiPartConverter())
            .client(clientWith30sTimeout)
            .build();

    WebAPIService service = retrofit.create(WebAPIService.class); //here is the interface which you have created for the call service
    Map<String, okhttp3.RequestBody> maps = new HashMap<>();

    if (fileUri!=null && fileUri.length>0) {
        for (int i = 0; i < fileUri.length; i++) {
            String filePath = getRealPathFromUri(fileUri[i]);
            File file1 = new File(filePath);

            if (filePath != null && filePath.length() > 0) {
                if (file1.exists()) {
                    okhttp3.RequestBody requestFile = okhttp3.RequestBody.create(okhttp3.MediaType.parse("multipart/form-data"), file1);
                    String filename = "imagePath" + i; //key for upload file like : imagePath0
                    maps.put(filename + "\"; filename=\"" + file1.getName(), requestFile);
                }
            }
        }
    }

    String descriptionString = " string request";//
    //hear is the your json request
    Call<String> call = service.postFile(maps, descriptionString);
    call.enqueue(new Callback<String>() {
        @Override
        public void onResponse(Call<String> call,
                               Response<String> response) {
            Log.i(LOG_TAG, "success");
            Log.d("body==>", response.body().toString() + "");
            Log.d("isSuccessful==>", response.isSuccessful() + "");
            Log.d("message==>", response.message() + "");
            Log.d("raw==>", response.raw().toString() + "");
            Log.d("raw().networkResponse()", response.raw().networkResponse().toString() + "");
        }

        @Override
        public void onFailure(Call<String> call, Throwable t) {
            Log.e(LOG_TAG, t.getMessage());
        }
    });
}
    
public String getRealPathFromUri(final Uri uri) { // function for file path from uri,
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT && DocumentsContract.isDocumentUri(mContext, uri)) {
        // ExternalStorageProvider
        if (isExternalStorageDocument(uri)) {
            final String docId = DocumentsContract.getDocumentId(uri);
            final String[] split = docId.split(":");
            final String type = split[0];

            if ("primary".equalsIgnoreCase(type)) {
                return Environment.getExternalStorageDirectory() + "/" + split[1];
            }
        }
        // DownloadsProvider
        else if (isDownloadsDocument(uri)) {

            final String id = DocumentsContract.getDocumentId(uri);
            final Uri contentUri = ContentUris.withAppendedId(
                    Uri.parse("content://downloads/public_downloads"), Long.valueOf(id));

            return getDataColumn(mContext, contentUri, null, null);
        }
        // MediaProvider
        else if (isMediaDocument(uri)) {
            final String docId = DocumentsContract.getDocumentId(uri);
            final String[] split = docId.split(":");
            final String type = split[0];

            Uri contentUri = null;
            if ("image".equals(type)) {
                contentUri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI;
            } else if ("video".equals(type)) {
                contentUri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI;
            } else if ("audio".equals(type)) {
                contentUri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
            }

            final String selection = "_id=?";
            final String[] selectionArgs = new String[]{
                    split[1]
            };

            return getDataColumn(mContext, contentUri, selection, selectionArgs);
        }
    }
    // MediaStore (and general)
    else if ("content".equalsIgnoreCase(uri.getScheme())) {

        // Return the remote address
        if (isGooglePhotosUri(uri))
            return uri.getLastPathSegment();

        return getDataColumn(mContext, uri, null, null);
    }
    // File
    else if ("file".equalsIgnoreCase(uri.getScheme())) {
        return uri.getPath();
    }

    return null;
}

public interface WebAPIService {
    @Multipart
    @POST("main.php")
    Call<String> postFile(@PartMap Map<String,RequestBody> Files, @Part("json") String description);
}