文件上传中的一个致命异常

public ActionForward execute(ActionMapping mapping, ActionForm form,

			final HttpServletRequest request, final HttpServletResponse response)

			throws Exception {

		

		ThreadPoolExecutor threadPool = (ThreadPoolExecutor) Executors.newCachedThreadPool();

		

		Properties config = getProperty(config_path);

        if (config == null) {

            config = loadConfig(config_path);

        }

        final String tempDir = config.getProperty("tempDir");//存储图片的临时目录

        final String photoDir = config.getProperty("photoDir");//照片目录

        final String photoUrl = config.getProperty("photoUrl");//照片的URL

        final String memorySize = config.getProperty("memorySize");//内存缓冲大小

        final String sizeMax = config.getProperty("sizeMax");//文件允许的最大值

        final String outTime = config.getProperty("outTime");//设置线程在终止前可以保持空闲的时间限制

        threadPool.setKeepAliveTime(Long.parseLong(outTime), TimeUnit.SECONDS);



		final PrintWriter out = response.getWriter();

		threadPool.execute(new Runnable() {

			public void run() {

				try {

					// 创建磁盘工厂

					DiskFileItemFactory factory = new DiskFileItemFactory();

					// 设置内存缓冲大小

					factory.setSizeThreshold(Integer.parseInt(memorySize));

					// 设置临时目录

					File file = new File(tempDir);

					if(!file.exists()){

						file.mkdir();

					}

					factory.setRepository(file);

					// 创建处理工具

					ServletFileUpload upload = new ServletFileUpload(factory);

					// 设置最大允许的尺寸

					int setFileSize = Integer.parseInt(sizeMax);

					int fileSize = request.getContentLength();

					upload.setSizeMax(setFileSize);

					

					if (fileSize <= setFileSize) {

						// 解析

						String contentType = request.getContentType();//multipart/form-data; boundary=p89nCm2-NdBgJFcZIdCixdGVgEbKHP

						if(contentType == null && "".equals(contentType)){

							out.print("File Upload Error");

							return;

						}

						List<FileItem> fileItems = upload.parseRequest(request);

						Iterator<FileItem> iter = fileItems.iterator();



						for (; iter.hasNext();) {



							FileItem fileItem = (FileItem) iter.next();

							// 判断FileItem类对象封装的数据是一个普通文本表单字段，还是一个文件表单字段，如果是普通表单字段则返回true，否则返回false

							if (fileItem.isFormField()) {

								// 当前是一个表单项

								out.print("form field : "

										+ fileItem.getFieldName() + ", "

										+ fileItem.getString());

							} else {

								// 当前是一个上传的文件

								String fileName = fileItem.getName();

								File fileDir = new File(photoDir + fileName);

								fileItem.write(fileDir);

								

								out.print(photoUrl + fileName);

							}

						}

					} else {

						out.print("你上传的文件过大");

					}

				}  catch (Exception e) {

					e.printStackTrace();

					out.print("File Upload Fail!");

				}

			}

		});

		return null;

	}