body>
  h2>上传图书课件/h2>
  form action="LimitFile" name="one" enctype="multipart/form-data" method="post">
    选择一个rar文件：
    input type="file" name="fileupload" value="upload" /> 
    input type="submit" value="上传"> input type="reset" value="取消">
  /form>
 /body> 

public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    request.setCharacterEncoding("utf-8");
    response.setCharacterEncoding("utf-8");
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();
    String uploadpath = "";
    DiskFileItemFactory factory = new DiskFileItemFactory();
    //设置是否使用临时文件保存解析出来的数据的那个临界值，该方法传入参数的单位是字节。
    factory.setSizeThreshold(30 * 1024);
    //用于设置setSizeThreshold()方法中提到的临时文件的存放目录，这里要求使用绝对路径。
    factory.setRepository(factory.getRepository());
    ServletFileUpload upload = new ServletFileUpload(factory);
    List list = null;
    try{
      list = upload.parseRequest(request);
      String[] limit = new String[]{".jpg", ".gif", ".png", ".bmp"};
      //定义限制的文件类型
      SuffixFileFilter filter = new SuffixFileFilter(limit);
      //获取SuffixFileFilter实例
      Iterator iterator = list.iterator();
      while(iterator.hasNext()){
        FileItem item =(FileItem)iterator.next();
        if(!item.isFormField()){
          String filePath = item.getName();
          if(filePath != null){
            File filename= new File(filePath);
            File uploadFile = new File(request.getSession().getServletContext().getRealPath("/") + "upload");
            uploadpath = uploadFile.getAbsolutePath()+File.pathSeparator + uploadpath;
            //因为路径后面多了个";"号，所以要去掉
            uploadpath = uploadpath.substring(0, uploadpath.length()-1);
            File saveFile = new File(uploadpath,filename.getName());
            boolean flag = filter.accept(saveFile);
            if(flag){
              out.print("禁止上传传图片文件");
              break;
            }else{
              try {
                item.write(saveFile);
                out.print("文件上传成功");
              } catch (Exception e) {
                out.print("文件上传失败了");
                e.printStackTrace();
              }
            }
          }
        }
      }
    }catch(FileUploadException e){
      e.printStackTrace();
    }
  }