关于文件下载的异常，怎么解决啊？

java.lang.IllegalStateException: getOutputStream() has already been called for this response每次都报这样的异常，这是我的源代码。请高手指教！
<%@ page contentType="text/html; charset=GBK" import="java.util.ArrayList"%><%@ page import="java.io.*" %>
<%@ page import="javax.servlet.ServletOutputStream" %>
<html>
<head>
</head>
<body>
<%request.setCharacterEncoding("GBK");
response.setCharacterEncoding("GBK");
String excelpath = (String)request.getAttribute("path");
String Path = excelpath.substring(3,excelpath.length());
if(excelpath!=null && !excelpath.equals(""))
{
  ServletOutputStream fo = null;
  BufferedOutputStream bos = null;
  BufferedInputStream bis = null;
  File temp = new File(excelpath);
  try
  {
    response.setContentType("application/vnd.ms-execl");
    response.setHeader("Content-Disposition","attachment;filename="+Path);
    bis = new BufferedInputStream(new FileInputStream(temp));
    fo = response.getOutputStream();
    bos = new BufferedOutputStream(fo);
    byte[] buff = new byte[2048];
    int bytesRead;
    while(-1 != (bytesRead = bis.read(buff, 0, buff.length)))
    {
      bos.write(buff,0,bytesRead);
    }
  }
  catch(Exception ex)
  {
    ex.printStackTrace();
  }
  finally
  {
    if(bos!=null)
    bos.close();
    if(bis!=null){
      bis.close();
    }
    fo.close();
    temp.delete();
  }%><% }
  else
  {
    out.println("11111111");
  }%>
  </body>
</html>