解决php下载excel无法打开的问题

<?php
/**
* php代码实现excel文件下载
* edit: www.jb200.com
*/
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 '<script>alert('export error, file not exists！')</script>';
  }