Excel file created with apache poi (Java) can't be opened on Windows

As Axel mentioned, the problem was the file extension.

I can open the files created this way in Ubuntu (Both 14.04 and 16.04), but not in Windows (7, 8 and 10).

The solution is to use the .xls extension and NOT .xlsx, that way I can open and use the files in any OS.

HSSF is the Office 97 *.xls format. (It stands for Horrible Spreadsheet Format.)

} catch (FileNotFoundException e) {
    workbook = new HSSFWorkbook();
}

When you did that, you chose the *.xls format. You need to use XSSFWorkbook if you want *.xlsx format.

https://poi.apache.org/components/spreadsheet/quick-guide.html#NewWorkbook

enter image description here

https://poi.apache.org/components/spreadsheet/

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