Get file name upload via form api?
The 'managed_file' FormElement plugin specifically stores the uploaded file as a managed file entity. This plugin stores the file entity id inside form state value as part of its validation.

  /**
   * {@inheritdoc}
   */
  public function submitForm(array &amp;$form, FormStateInterface $form_state) {
    drupal_set_message($this-&gt;t('@can_name ,Your application is being submitted!', array('@can_name' =&gt; $form_state-&gt;getValue('name'))));
    // Use the fid to load the file entity. Unfortunately ManagedFile loads the file entity, but does not store it in form state.
    $fid = $form_state-&gt;getValue('resume');
    $file = \Drupal\file\Entity\File::load($fid);
    // Do something other than "echo" $file-&gt;getFilename() here.
  }