java实现文件上传功能

<dependency>
 <groupId>commons-fileupload</groupId>
 <artifactId>commons-fileupload</artifactId>
 <version>1.3.3</version>
</dependency>

<form action="/file.do" enctype="multipart/form-data" method="post">
 <p>上传用户:<input type="text" name="username"></p>
 <p><input type="file" name="file1"></p>
 <p><input type="file" name="file2"></p>
 <p><input type="submit">|<input type="reset"></p>
</form>

protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
  //判断上传的是普通表单还是带文件的表单
  if (!ServletFileUpload.isMultipartContent(req)) {
   return;
  }
  //创建上传文件保存的地址，一般创建在WEB-INF目录下，用户无法直接访问该目录下的文件
  String uploadPath = this.getServletContext().getRealPath("/WEB-INF/upload");
  File uploadFile = new File(uploadPath);
  //如果文件夹不存在，则创建一个
  if (!uploadFile.exists()) {
   uploadFile.mkdir();
  }

  //创建上传大文件的临时地址，一般几天后自动删除，用户可以手动删除或者转为永久文件
  // 一般创建在WEB-INF目录下，用户无法直接访问该目录下的文件
  String tempPath = this.getServletContext().getRealPath("/WEB-INF/temp");
  File tempFile = new File(tempPath);
  //如果文件夹不存在，则创建一个
  if (!tempFile.exists()) {
   tempFile.mkdir();
  }

  //1.创建diskFileItemFactory对象，处理文件上传路径或者大小限制
  DiskFileItemFactory factory = getDiskFileItemFactory(tempFile);

  //2.获取ServletFileUpload
  ServletFileUpload upload = getServletFileUpload(factory);

  //3.处理上传的文件
  try {
   String msg = uploadParseRequest(upload, req, uploadPath);
   //转发
   req.setAttribute("msg",msg);
   req.getRequestDispatcher("info.jsp").forward(req, resp);
  } catch (FileUploadException e) {
   e.printStackTrace();
  }
 }


 public DiskFileItemFactory getDiskFileItemFactory(File file) {
  DiskFileItemFactory factory = new DiskFileItemFactory();
  //创建一个缓存区，当上传文件大于设置的缓存区时，将该文件放到临时目录
  factory.setSizeThreshold(1024 * 1024);//缓存区大小为1M
  factory.setRepository(file);//临时目录
  return factory;
 }

 public ServletFileUpload getServletFileUpload(DiskFileItemFactory factory) {
  ServletFileUpload upload = new ServletFileUpload(factory);
  //监听文件上传进度
  upload.setProgressListener(new ProgressListener() {
   @Override
   public void update(long uploaded, long totalSize, int i) {
    System.out.println("已上传："+(uploaded*100)/totalSize+"%");
   }
  });
  upload.setHeaderEncoding("UTF-8");//乱码处理
  upload.setFileSizeMax(1024 * 1024 * 10);//设置单个文件的最大值10M
  upload.setSizeMax(1024 * 1024 * 100);//设置总共能上传文件的最大值100M
  return upload;
 }

 public String uploadParseRequest(ServletFileUpload upload, HttpServletRequest req, String uploadPath) throws FileUploadException, IOException {
  String msg = "";
  //把前端请求解析，封装成一个List对象
  List<FileItem> fileItems = upload.parseRequest(req);
  for (FileItem fileItem : fileItems) {
   if (fileItem.isFormField()) {//判断上传的文件是普通的表单还是带文件的表单
    String name = fileItem.getName();//前端表单控件的name：username
    String value = fileItem.getString("UTF-8");//乱码处理
    System.out.println(name + ":" + value);
   } else {//判断为上传的文件
    //==================处理文件=====================
    String uploadFileName = fileItem.getName();//前端表单控件的name
    System.out.println("上传的文件名:" + uploadFileName);
    if (uploadFileName.trim().equals("") || uploadFileName == null) {//可能存在不合法的情况
     continue;
    }
    String fileName = uploadFileName.substring(uploadFileName.lastIndexOf("/") + 1);//文件名
    String fileExtName = uploadFileName.substring(uploadFileName.lastIndexOf(".") + 1);//文件后缀名
    System.out.println("文件名：" + fileName + "--文件后缀：" + fileExtName);
    //==================存放地址==================
    String uuidPath = UUID.randomUUID().toString();
    //文件存储的真实路径
    String realPath = uploadPath + "/" + uuidPath;
    System.out.println("文件上传到的位置:"+realPath);
    //给每个文件创建一个文件夹
    File realPathFile = new File(realPath);
    if (!realPathFile.exists()) {//如果文件夹不存在，则创建一个
     realPathFile.mkdir();
    }
    //==================文件传输==================
    //获得文件上传的流
    InputStream inputStream = fileItem.getInputStream();
    //创建一个文件输出流
    FileOutputStream fileOutputStream = new FileOutputStream(realPath + "/" + fileName);
    //创建一个缓冲区
    byte[] buffer = new byte[1024 * 1024];
    //判断读取是否完毕
    int len = 0;
    while ((len = inputStream.read(buffer)) > 0) {
     fileOutputStream.write(buffer, 0, len);
    }
    //关闭流
    fileOutputStream.close();
    inputStream.close();
    msg = "上传成功";
    fileItem.delete();//上传成功，清除临时文件
   }
  }
  return msg;
}