求解servlet中流的问题！

public class DownloadServlet extends HttpServlet {



    protected void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {



        //通过get方式取得文件名

        String filename = request.getParameter("filename");//movie.mp4



        response.setContentType(this.getServletContext().getMimeType(filename));

   

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



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



        InputStream in = new FileInputStream(path);



        ServletOutputStream out = response.getOutputStream();

        //实现IO

        int len = 0;

        byte[] buffer = new byte[1024];

        while((len=in.read(buffer))>0){

            out.write(buffer, 0, len);

        }



        in.close();



    }



    protected void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        doGet(request, response);

    }

}