1、将commons-fileupload-1.3.3.jar复制到Web应用的lib文件夹下，在WebRoot目录下创建limit.jsp页面，在该页面中添加一个文件域的表单，设置类型为 multipart/form-data。代码如下：
<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>
上述代码指定提交后将请求提交给LimitFile处理，LimitFile(Servlet)用来处理上传文件及判断文件类型是否匹配，显示上传结果。
2、创建名为LimitFile的Servlet，并在doPost()方法中编写实现代码，如下所示：
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(); } }
上述代码在字节串数组limit中定义了不允许上传的文件类型，然后将该数组传递给SuffixFileFilter类的构造函数。在通过该类的accept()方法验证当前上传的文件是否符合条件。最后将文件保存到项目的upload目录下。