用Jsp来实现文件下载功能的几种方式

URLConnection con;
        try {
            con = url.openConnection();
            //url是被调用的SERVLET的网址 如 *.do         
　　        con.setUseCaches(false);
            con.setDoInput(true);
            con.setDoOutput(true);
            con.setRequestProperty("Content-Type","application/octet-stream");  
            OutputStream out = con.getOutputStream();
            //localfilepath本地路径,localstr文件文件夹，filename本地文件名
            String localfilepath = localstr + filename;
            //文件getOutputStream是把文件localfilepath写到输出流out中
            getOutputStream(localfilepath,out);
            InputStream in = con.getInputStream();
            return true;
        }catch (IOException e) {
               System.out.println("文件上传出错！");
            e.printStackTrace();
        }