用Jsp来实现文件下载功能的几种方式

public void service(HttpServletRequest req, HttpServletResponse res)
            throws ServletException, IOException {
        res.setContentType(" text/plain ");
        OutputStream outputStream = null;
        try {
            outputStream = res.getOutputStream();
            //把文件路径为srcFile的文件写入outputStream中
            popFile(srcFile, outputStream)) ;
     
        } catch (IOException e) {
            e.printStackTrace();    
     }
    }