使用ServletFileUpload实现上传

1.首先我们应该为上传的文件建一个存放的位置，一般位置分为暂时和真是目录，那我们就须要获取这俩个目录的绝对路径，在servlet中我们能够这样做

		ServletContext application = this.getServletContext();
		String tempDirectory = application.getRealPath(Constant.TEMP_DIRECTORY) + "/";
		String realDirectory = application.getRealPath(Constant.REAL_DIRECTORY) + "/";

		FileItemFactory factory = new DiskFileItemFactory(Constant.SIZE_THRESHOLD,new File(tempDirectory));
		ServletFileUpload upload = new ServletFileUpload(factory);

		upload.setSizeMax(500*1024*1024);//设置该次上传最大值为500M

List<FileItem> list = upload.parseRequest(request);
			Iterator<FileItem> iter = list.iterator();
			while (iter.hasNext()) {
				FileItem item = iter.next();
				//item.isFormField()用来推断当前对象是否是file表单域的数据  假设返回值是true说明不是 就是普通表单域
				if(item.isFormField()){
					System.out.println( "普通表单域" +item.getFieldName());
					System.out.println(item.getString("utf-8"));

				}else{
					//System.out.println("file表单域" + item.getFieldName());
					/*
					 * 仅仅有file表单域才将该对象中的内容写到真实目录中 
					 */
					String lastpath = item.getName();//获取上传文件的名称
					lastpath = lastpath.substring(lastpath.lastIndexOf("."));
					String filename = UUID.randomUUID().toString().replace("-", "") + lastpath;
					item.write(new File(realDirectory+filename));