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;
}