Que dois-je faire si le fichier de téléchargement php ne peut pas être ouvert ?

if (file_exists(CACHE_PATH . $file_name)){
            //$this->logger->error('file realpath:'.realpath(CACHE_PATH . $file_name));
      header( 'Pragma: public' );
      header( 'Expires: 0' );
      header( 'Content-Encoding: none' );
      header( 'Cache-Control: must-revalidate, post-check=0, pre-check=0' );
      header( 'Cache-Control: public' );
   header( 'Content-Type: application/vnd.ms-excel'); 
      header( 'Content-Description: File Transfer' );
      header( 'Content-Disposition: attachment; filename=' . $file_name );
      header( 'Content-Transfer-Encoding: binary' );
      header( 'Content-Length: ' . filesize ( CACHE_PATH . $file_name ) );
      readfile ( CACHE_PATH . $file_name );
  } else {
   $this->logger->error('export model :'.$id.' 错误：未生产文件');
      echo &#39;<script>alert(\&#39;export error, file not exists！\&#39;)</script>&#39;;
  }