servlet getWriter() has already been called for this response

Servlet代码：
OutputStream os = response.getOutputStream();
response.setContentType("application/msexcel");
response.setHeader("Content-disposition","attachment;   filename=Excel1.xls");
报错：getWriter() has already been called for this response
解决办法：
response.reset();加入这句就搞定了
OutputStream os = response.getOutputStream();
response.setContentType("application/msexcel");
response.setHeader("Content-disposition","attachment;   filename=Excel1.xls");