poi-3.9通过模板构建的excel2007工作簿读取不到模板的内容

public static void testcopy() throws FileNotFoundException, IOException{
File file = new File("D://Earlyreturn.xlsx");
XSSFWorkbook sw = new XSSFWorkbook(new FileInputStream(file));
SXSSFWorkbook sxw = new SXSSFWorkbook(sw,1000);
SXSSFSheet sheet = (SXSSFSheet) sxw.getSheetAt(0);
System.out.println(sheet.getSheetName());//可以读取sheet的名称
System.out.println(sheet.getRow(0));//读取不到，为null
}
/*
* 官方解释：
There are three use-cases to use SXSSFWorkbook(XSSFWorkbook) :
1.Append new sheets to existing workbooks. You can open existing workbook from a file or create on the fly with XSSF.
2.Append rows to existing sheets. The row number MUST be greater than max(rownum) in the template sheet.
3.Use existing workbook as a template and re-use global objects such as cell styles, formats, images, etc.
All three use cases can work in a combination.

What is not supported:
•Access initial cells and rows in the template. After constructing SXSSFWorkbook(XSSFWorkbook) all internal windows are empty and SXSSFSheet@getRow and SXSSFRow#getCell return null.
•Override existing cells and rows. The API silently allows that but the output file is invalid and Excel cannot read it.
* */
}