@WebServlet("/download")

public class DownloadServlet extends HttpServlet{

    @Override

    protected void service(HttpServletRequest req, HttpServletResponse resp)

            throws ServletException, IOException {

        resp.setCharacterEncoding("utf-8");

        resp.setContentType("application/octet-stream");

        //解决 以文件形式下载 而不会被浏览器打开    以及中文文件名需要编码

        resp.setHeader("Content-Disposition", "attachment;filename="+URLEncoder.encode("中国", "utf-8")+".txt");

        PrintWriter os = resp.getWriter();

        String path = this.getServletContext().getRealPath("/download");

        Reader is = new BufferedReader(new FileReader(new File(path,"t.txt")));

        int len=0;

        char[] buffer = new char[200];

        while((len=is.read(buffer))!=-1){

            os.print(new String(buffer,0,len));

        }

        is.close();

        os.close();

    }

}