servlet实现文件下载

public void execute(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
	response.setContentType("application/download");
	String filename=request.getParameter("fileName");
	String sourceName= filename;
	filename=new String(filename.getBytes("UTF-8"),"ISO8859-1");
	response.addHeader("content-Disposition", "attachment;filename=\"" + filename + "\"");
		
	InputStream in =new FileInputStream(request.getServletContext().getRealPath("upload/" + sourceName));
	ServletOutputStream out = response.getOutputStream();
		
	byte[] buf=new byte[1024];
	int len=-1;
	while((len=in.read(buf, 0, buf.length))!=-1){
		out.write(buf, 0, len);
	 out.flush();
	}
	in.close();
	out.close();
}