java – Excel读取错误：标头签名无效.怎么解决？

在我使用的两个jsp文件下面：
JSP 1：

<form action="Upload.jsp" enctype="MULTIPART/FORM-DATA" method=post >
  <input type="file" name="filename" />
  <input type="submit" value="Upload" />
</form>

JSP 2：Upload.jsp

try{
        InputStream file = request.getInputStream();
        POIFSFileSystem myFileSystem = new POIFSFileSystem(file);
        hssfWorkbook myWorkBook = new hssfWorkbook(myFileSystem);
        hssfSheet mySheet = myWorkBook.getSheetAt(0);
        Iterator rowIter = mySheet.rowIterator();
        rowIter.next(); 
        while (rowIter.hasNext()) {
            hssfRow myRow = (hssfRow) rowIter.next();
            Iterator cellIter = myRow.cellIterator();
            cellIter.next();
            System.out.println(((hssfCell)cellIter.next()).toString());
        }


    }catch(Exception ex){
        System.out.println(ex.getMessage());
    }

但是在POIFSFileSystem myFileSystem =新的POIFSFileSystem(文件)中获取错误;

如何解决这个问题？