jsp文件下载的问题,RequestDispatcher的方式

我用RequestDispatcher的方式进行文件下载,为啥每次都只能下载20%就下载失败了
代码如下:
<%

response.setContentType("application/octet-stream");
String filedownload = request.getParameter("filePath_KC");
String filedisplay = request.getParameter("fileName_KC");
String filenamedisplay = URLEncoder.encode(filedisplay,"UTF-8");

response.addHeader("Content-Disposition","attachment;filename=" + filedisplay);

try

{

RequestDispatcher dis = application.getRequestDispatcher(filedownload);

if(dis!= null)

{

dis.forward(request,response);

}

response.flushBuffer();

}

catch(Exception e)

{

e.printStackTrace();

}

finally

{

}

不用这句。response.flushBuffer();