sheet.getRow(0)获取的row为null？

new SXSSFWorkbook(new XSSFWorkbook(inputStream));
这种方式创建的Workbook，使用sheet.getRow(0)获取的row为null；

原因是new SXSSFWorkbook(new XSSFWorkbook(inputStream))的时候，SXSSFWorkbook对象内部会维护一个HashMap(反编译后的名称为_xFromSxHash)；

当使用workBok.getSheetAt(0)的时候，其实是从_xFromSxHash中获取新创建的Sheet对象；从而导致sheet.getRow(0)获取的row为null。

Workbook workBook = new SXSSFWorkbook(new XSSFWorkbook(inputStream));
Sheet sheet = workBook.getSheetAt(0);
Row row = sheet.getRow(0);

改为如下取值即可：

Workbook workBook = new SXSSFWorkbook(new XSSFWorkbook(inputStream));
Sheet sheet;
if (workBook instanceof SXSSFWorkbook) {
   SXSSFWorkbook sxssfWorkbook = (SXSSFWorkbook) workBook;
   sheet = sxssfWorkbook.getXSSFWorkbook().getSheetAt(sheetIndex);
} else {
   sheet = workBook.getSheetAt(sheetIndex);
}
Row row = sheet.getRow(0);