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);