$image_data = file_get_contents($thumbnail);
$filename = basename($thumbnail);

file_put_contents($thumbnail, $image_data);

$wp_filetype = wp_check_filetype($filename, null );
$attachment = array(
    'post_mime_type' => $wp_filetype['type'],
    'post_title' => sanitize_file_name($filename),
    'post_content' => '',
    'post_status' => 'inherit'
);
$attach_id = wp_insert_attachment( $attachment, $thumbnail, $postId );
require_once(ABSPATH . 'wp-admin/includes/image.php');
$attach_data = wp_generate_attachment_metadata( $attach_id, $thumbnail );
$res1= wp_update_attachment_metadata( $attach_id, $attach_data );
  update_post_meta( $postId, '_thumbnail_id', $attach_id );

<img width="350" height="421" src="http://localhost/w/wp-content/uploads/https://1.bp.blogspot.com/-yL4P2_f5ygk/Vxx2SBGRrII/AAAAAAAANL0/pfK0uEWrRTwZuJoq0UuwxNHpXMQ4ouypQCLcB/s1600/Step%2BUp%2BRevolution%2B2012%2BDual%2BAudio%2BHindi%2BBluRay.jpg"  class="attachment-post-thumbnail size-post-thumbnail wp-post-image"  alt="Step2BUp2BRevolution2B20122BDual2BAudio2BHindi2BBluRay.jpg" />