uploadify build: 3.2.1

核心代码
html: <tr><td><div id="fileQueue"></div></td></tr>
    <tr><td colspan="2">上传证件：<input id="uploadify" type="file"  multiple="true"/><p>
     <a href="javascript:$('#uploadify').uploadify('upload','*')">开始上传</a>| 
     <a href="javascript:$('#uploadify').uploadify('cancel','*')">取消上传</a>
    </p>支持上传的类型：<span class="bt_n">png、jpg、gif、jpeg。</span></td></tr>
js:$("#uploadify").uploadify({
'method':"post",
        'uploader':tool.getRootPath()+"upload/uploadimg.action",
        'swf' : tool.getRootPath()+"static/plugins/uploadify/uploadify.swf",
       //'checkExisting' :tool.getRootPath()+"upload/uploadimg.action",
       //'buttonImage': tool.getRootPath()+"static/plugins/uploadify/uploadify-cancel.png",
        'fileSizeLimit' : '1MB',
        'fileTypeExts' : '*.gif; *.jpg; *.png; *.jpeg',
        'fileTypeDesc' : "支持上传的类型：gif、jpg、png、jpeg",
        'queueID': 'fileQueue',
        'auto'           : false,
        'multi'          : true,
        'simUploadLimit' : 2,
        'removeTimeout' : 10,
        'buttonText'     : '浏览'
    });
java action:
public class UploadAction  extends BaseAdminAction{
private static Logger logger = Logger.getLogger(UploadAction.class);
private File uploadify;
private String uploadifyFileName;
private String filepath;
/**
 * 上传图片
 * @return 图片路径
 */
@Action(value="uploadimg",results={@Result(name="uploadimg",type="json",params={"root","filepath"})})
public String uploadimg(){
String savePath = ServletActionContext.getServletContext().getRealPath("/UploadFile");//上传完后文件存放位置  
System.out.println(savePath);  
        String newsuffix = "";  
        String current=new java.text.SimpleDateFormat("yyyyMMdd").format(new Date());
        if((uploadifyFileName != null)&&(uploadifyFileName.length()>0))  
        {  
            int dot = uploadifyFileName.lastIndexOf(".");  
            if((dot >-1) && (dot < (uploadifyFileName.length() - 1)))  
            {  
                 newsuffix = uploadifyFileName.substring(dot + 1);  
            }  
        }
        try {
        FileInputStream fis = new FileInputStream(uploadify);
        filepath = savePath+"/"+current + "." + newsuffix;
        FileOutputStream fos = new FileOutputStream(filepath);  
        IOUtils.copy(fis, fos);  
        fos.flush();  
        fos.close();  
        fis.close();  
        } catch (Exception e) {
logger.error("图片上传错误", e);
filepath="";
}
return "uploadimg";
}
在进入uploadimg方法时  uploadify，uploadifyFileName为NULL 求小伙伴们指点