问无法使用JExcelApi在现有excel中写入测试结果

EN

      String usernamevalidationmsg = a.findElement(By.id("UserNameRequired")).getText()

      String usernamevalidationexpected = "Email is required.";

      if (usernamevalidationmsg.equals(usernamevalidationexpected))
      {
        try
        { 
                   FileOutputStream f = new FileOutputStream("D:\\seleniumreport.xls",true);
                   WritableWorkbook book = Workbook.createWorkbook(f);
                   WritableSheet sheet = book.getSheet(0);
                   Label l = new Label(1, 2, "Pass");
                   sheet.addCell(l);
                   book.write(); 
                   book.close(); 
         }
         catch (Exception e)
         {
                   e.printStackTrace();
         }