Struts上传文件出错，请大神帮忙看一下?报错

报错内容如下：

public class FileAction {
 private File upload;
 private String uploadFileName;
 private String uploadContentType;

 public String upload() {
  byte[] buffer = new byte[1024];
  String path = ServletActionContext.getServletContext().getRealPath(
    "/upload/" + this.uploadFileName);
  System.out.println(path);
  // 设置上传文件目录

  FileInputStream fis = new FileInputStream(upload);  //报错应该转为String类型
  FileOutputStream fos = new FileOutputStream(path);
  IOUtils.copy(fis, fos);
  fos.flush();
  fos.close();
  fis.close();
  return "success";
 }