How to Upload Files to the Server With the File Upload API

by on September 1, 2019

There are several ways to upload file content to the server:

  1. The traditional approach where a physical file from the client environment is uploaded using the API.
  2. Creating a remote file with content generated on the client-side.

In this article, we will review the first option – uploading a file with the API.

Once a file is uploaded, the File Service enables the following:

  • You can see the file in File Browser in Backendless Console.
  • The file can be downloaded via a URL assigned to it. The URL is composed as:<application id>/<version name>/files/<path>/<file name>
  • The application developer can assign permissions to control who (users or roles) can download or delete the file.
  • If git integration is enabled for the application; the file is also committed to the repository.

The example below demonstrates the API for file upload:

       // create a file locally so there is something to upload
       String filename = "myhelloworld-async.txt";
       FileOutputStream fileOutputStream = new FileOutputStream(filename);
       fileOutputStream.write("Hello mbaas!\nUploading files is easy!".getBytes());
       final File file = new File(filename);
       // now upload the file
       Backendless.Files.upload(file, "/myfiles", new AsyncCallback() {
           public void handleResponse(BackendlessFile uploadedFile) {
               Log.i(TAG, "File has been uploaded. File URL is - " + uploadedFile.getFileURL());
           public void handleFault(BackendlessFault fault) {
               Log.e(TAG, fault.getMessage());

       // create a file locally so there is something to upload
       val filename = "myhelloworld-async.txt"
       val fileOutputStream = FileOutputStream(filename)
       fileOutputStream.write("Hello mbaas!\nUploading files is easy!".toByteArray())
       val file = File(filename)
       // now upload the file
       Backendless.Files.upload(file, "/myfiles", object : AsyncCallback {
           override fun handleResponse(uploadedFile: BackendlessFile) {
               Log.i(TAG, "File has been uploaded. File URL is - ${uploadedFile.fileURL}")
           override fun handleFault(fault: BackendlessFault) {
               Log.e(TAG, fault.message)

    // create a file data so there is something to upload
    NSData *data = [@"Hello mbaas!\nUploading files is easy!" dataUsingEncoding:NSUTF8StringEncoding];
    // now upload the file
    [Backendless.shared.file uploadFileWithFileName:@"myhelloworld.txt" filePath:@"myfiles" content:data overwrite: YES responseHandler:^(BackendlessFile *uploadedFile) {
        NSLog(@"File has been uploaded. File URL is - %@", uploadedFile.fileUrl);
    } errorHandler:^(Fault *fault) {
        NSLog(@"Error: %@", fault.message);

    // create a file data so there is something to upload
    if let data = "Hello mbaas!\nUploading files is easy!".data(using: .utf8) {
        // now upload the file
        Backendless.shared.file.uploadFile(fileName: "myhelloworld.txt", filePath: "myfiles", content: data, overwrite: true, responseHandler: { uploadedFile in
            print("File has been uploaded. File URL is - \(uploadedFile.fileUrl ?? "")")
        }, errorHandler: { fault in
            print("Error: \(fault)")

    const Backendless = require('backendless')
     Or use `import Backendless from 'backendless'` for client side.
     If you don't use npm or yarn to install modules, you can add the following line
     <script src="//"></script>
     to your index.html file and use the global Backendless variable.
    Backendless.initApp('YOUR_APP_ID', 'YOUR_JS_API_KEY')
    const handleFileSelect = event => {
      const { files } = // FileList object
      for (let file of files) {
        Backendless.Files.upload(file, '/myFiles')
          .then(onSuccess, onError)
    const onSuccess = file => {
      console.log('Uploaded file URL - ' + file.fileURL)
    const onError = error => {
      console.error('Server reported an error: ', error.message)
      console.error('error code: ', error.code)
      console.error('http status: ', error.status)

       // create a file locally so there is something to upload
       String filename = "myhelloworld-async.txt";
       File file = await File(filename).writeAsString("Hello mbaas!\nUploading files is easy!");
       Backendless.Files.upload(file, "/myfiles").then((response) {
         print("File has been uploaded. File URL is - " + response);

    When you run the code and the files are uploaded, you can see them in Backendless Console. To do that:
    1. Login to Console, select your app and click the Files icon.
    2. You will see the “myfiles” directory created by the code above. Click the directory name to see its contents.
    3. You should see two files as shown in the screenshot below.
    4. To see the contents of the file, click the Edit file icon:



    I have created some files in the root directory some years ago and overwrite them with new uploaded data from my apps. With the new Swift API, I need to specify the “filePath” which was not required in the Objective-C API. How to set the “filePath” parameter to upload files to the root directory like it used to be? Thanks.

    I didn’t get the part of how to integrate backendless into my swift project.

    Please see this for instructions on how to integrate Backendless into your Swift project:

    What is the maximum size of file

    Hi Vinod, the maximum upload file size is 1 GB.

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