Formdata图片传输，java后台解析问题

这是前端代码：
var formdata = new FormData();
formdata.append("files",files);
var json = {"files":files};
$.ajax({
type: "post",
url: "http://localhost:8080/Ajax1/practise",
async: true,
data: "files="+formdata,
dataType: "text",
success: function(data) {

            alert(data);
        },
        error: function() {
            alert("登录出错");
        }
    }); 


    java后台要什么解析，通过
    String fi = request.getParameter("files");

    输出是个对象
    [object FormData]

    要怎么解析formdata

已解决
DiskFileItemFactory factory = new DiskFileItemFactory();
ServletFileUpload upload = new ServletFileUpload(factory);

    try {
        List<FileItem> items = upload.parseRequest(request);
        System.out.println("1:=========" + items.size());
        Map param = new HashMap();
        for (Object object : items) {
            FileItem fileItem = (FileItem) object;
            System.out.println("2:=========" + fileItem.toString());
            System.out.println("3：fileItem.getFieldName():==" + fileItem.getFieldName());

            if (fileItem.isFormField()) {
                param.put(fileItem.getFieldName(),
                        fileItem.getString("utf-8"));// 如果你页面编码是utf-8的
                System.out.println("4: param.get(fileItem.getFieldName())==="
                        + param.get(fileItem.getFieldName()));
            } else {

                String picturename =fileItem.getName();

                String path = "D:\\temp\\" + picturename;
                System.out.println("======================="+path+"==========");
                String path2 = "D:\\k\\java开发\\Hbuilder\\ajaxServlet1\\img\\"
                        + fileItem.getName();
                fileItem.write(new File(path));
            }
        }

慕课网有视频，你可以去看看