下载中文名的文件显示文件不存在，下载不带中文的能成功
String path = getServletContext().getRealPath("/") + "material/";
String filename = req.getParameter("filename");
File file = new File(path + filename);
if(file.exists()){
//设置相应类型application/octet-stream
resp.setContentType("application/x-msdownload");
//设置头信息
resp.setHeader("Content-Disposition", "attachment;filename=\"" + filename + "\"");
InputStream inputStream = new FileInputStream(file);
ServletOutputStream ouputStream = resp.getOutputStream();
byte b[] = new byte[1024];
int n ;
while((n = inputStream.read(b)) != -1){
ouputStream.write(b,0,n);
