JavaWebservlet如何实现下载与上传功能

protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {
    // 1.获取下载目标
    String filename = request.getParameter("target");
    System.out.println(filename);
    // 2.找到下载目标
    String path = getServletContext().getRealPath("download/" + filename);
    File file = new File(path);
    if (file.exists()) {
      // 3.如果文件存在，那么设置响应的内容为下载，告诉浏览器将信息识别成下载
      // 判断一下浏览器
      String agent = request.getHeader("User-Agent");
      if (agent.contains("Firefox")) {// 火狐
        BASE64Encoder base64Encoder = new BASE64Encoder();
        filename = "=?utf-8?B?" + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
      } else {// ie和谷歌
        filename = URLEncoder.encode(filename, "utf-8");
      }
      response.setHeader("Content-Disposition", "attachment; filename=" + filename);
      // 4.获取文件流
      FileInputStream fis = new FileInputStream(file);
      OutputStream os = response.getOutputStream();
      // 5.返回给浏览器
      int len = 0;
      byte[] buffer = new byte[1024];
      while ((len = fis.read(buffer)) != -1) {
        os.write(buffer, 0, len);
      }
      os.flush();// flush一下，确保一下
      os.close();
      fis.close();
    } else {
      response.setContentType("text/html;charset=UTF-8");
      response.getWriter().write("找不到文件");
    }

  }

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    request.setCharacterEncoding("utf-8");
    DiskFileItemFactory factory=new DiskFileItemFactory();//1.创建DiskFileItemFactory工厂类
    ServletFileUpload upload=new ServletFileUpload(factory);//2.创建解析类，用于解析resquest
    try {
      List list = upload.parseRequest(request);//3.解析内容，获取一个list，数据都存储在list中
      for(FileItem item:list) {
        if(item.isFormField()) {//判断是否是普通的表单内容
          System.out.println(item.getFieldName());//获取的是表单中name属性的值
          System.out.println(item.getString());//获取的是对应的表单的值
        }else {//为假，说明是上传项
          //获取流，进行处理
          InputStream ism = item.getInputStream();
          String path=getServletContext().getRealPath("/upload/");
          System.out.println(path);
          String filename = item.getName();//这里getName可以获取文件名
          System.out.println(filename);
          File file=new File(path+filename);
          file.createNewFile();//这里不做文件存在性和名字重复判断
          OutputStream fos = new FileOutputStream(file);
          //这里直接借助commons.io来做io对接，不然需要做流的读取和写入
          IOUtils.copy(ism,fos);//把输入流的数据拷贝到输出流
          IOUtils.closeQuietly(ism);
          IOUtils.closeQuietly(fos);
          
        }
      }
    } catch (FileUploadException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    
    
  }