Apache POI: Transfer time from cell to cell - apache-poi

Question

Need in short: I'd like to copy a time value from one cell to another cell.
Problem in short: POI 5.2.2 (or more specific: DateUtil.internalGetExcelDate) transforms the 08:00 o'clock from the input cell to the numeric value -1.00.
More details: There's an xlsx file (created with LibreOffice 7.0.4.2) with the time '08:00:00' in it:
I can read that value with sourceCell.getLocalDateTimeCellValue(), which is fine.
But when I try to transfer that value into another cell (targetCell.setCellValue(sourceCell.getLocalDateTimeCellValue())), in the targetCell there is the value -1 instead of the expected 08:00:00 o'clock.
Here's a screenshot while debugging the setCellValue call:
And here's a screenshot while debugging the DateUtil.internalGetExcelDate call:
Possible workaround: I guess that it would work to evaluate the LocalDateTime from the sourceCell and if its year is < 1904 then I add some years to that the resulting LocalDateTime is not transformed to -1.00 by DateUtil.internalGetExcelDate.
This is something I don't want to do because that would set another value in the targetCell than there was in the sourceCell.
Another workaround: Another workaround would be to use LocalDateTime.now(), set the hour and minute, call targetCell.setCellValue(...) and then change the format like this:
short format = workbook.createDataFormat().getFormat("HH:MM:SS");
CellStyle cellStyle = workbook.createCellStyle();
cellStyle.setDataFormat(format);
targetCell.setCellStyle(cellStyle);
Unfortunately I don't know whether the sourceCell just contains a time or whether it contains a full timestamp. I just want to copy cell contents (which works fine with String, Number, ...).
Actual workaround: As a current (working) workaround I check the year and if it's <1900 then I set another year at the date, set the modified LocalDateTime into the cell and set the dataformat (see workaround description above).
Question: How can I transfer a LocalTime value from one cell to another cell (without manipulating the year)? I guess that my (working) workaround should not be the answer ...

Answer 1

Excel cell date types
Microsoft Excel only has following cell data types:
String (alphanumeric)
Numeric (floating point number)
Boolean (true or false)
Formula (formula strings)
Error (internally error codes)
Empty (empty cell)
There is no special date cell data type as well as no special Integer cell date type.
How Excel stores date or time or date-time
If Excel stores date-time, it stores it as floating point number. There 1.00 is 1900-01-01 00:00:00.000. (There is a special case when Excel has set 1904-Date. But that is a special case only about the meaning of 1.00.).
Adding 1.00 means adding one day. Adding 1/24 means adding one hour. Adding 1/24/60 means adding one minute. Adding 1/24/60/60 means adding one second. Adding 1/24/60/60/10 means adding a tenth second and so on.
For cell values lower than 1.00, Excel interprets that as time in day 0 of month 1 in year 1900 (or 1904 if Excel has set 1904-Date). There 1/24 means one hour. 1/24 + 1/24/60 means one hour and one minute and so on. So your 08:00:00 is the cell value 8*1/24 (8 hours) = 1/3.
When reading Excel cell values the only way to determine whether Excel interprets a cell value as a date or time or date-time is to get the cell's number format too. If that is a date or time or date-time format, then Excel interprets a cell value of 1.00 as 1900-01-01, a cell value of 1/24 as 01:00:00, a cell value of 1/24 + 1/24/60 as 01:01:00 and so on.
But your observation is correct. If Apache POI reads a date-time from an Excel cell which has set only a time, which is a numeric (double) value between 0.00 and 1.00, then it reads a date-time of day 1899-12-31. But that is not what Excel does. For Excel the time-only value is in day 0 of month 1 in year 1900. If then Apache POI sets a date-time value of, for example 1899-12-31 08:00:00, then it sets -1 because Excel cannot have date-time values before 1900.
So the only way to set time values in Excel cells is to set numeric (double) values between 0.00 and 1.00 and set a cell style having a number format of HH:MM:SS. One cannot set a time only Excel cell value from a Java date-time value, because there is not a Java date-time value which can have day 0 of month 1 in year 1900.
So if DateUtil.isCellDateFormatted tells that the source cell is date formatted and the numeric (double) cell value of that cell is lower than 1, then set that numeric (double) cell value to the new cell and format that cell the same as the source cell.
Complete example to test:
import java.io.FileInputStream;
import java.io.FileOutputStream;
import org.apache.poi.ss.usermodel.*;
public class ExcelSetCellValue {
public static void main(String[] args) throws Exception {
Workbook workbook = WorkbookFactory.create(new FileInputStream("./ExcelWithTime.xlsx")); String filePath = "./ExcelWithTimeNew.xlsx";
//Workbook workbook = WorkbookFactory.create(new FileInputStream("./ExcelWithTime.xls")); String filePath = "./ExcelWithTimeNew.xls";
Sheet sheet = workbook.getSheetAt(0);
Cell sourceCell = sheet.getRow(0).getCell(0); // get cell value from A1: 08:00:00
Row targetRow = sheet.getRow(5); if (targetRow==null) targetRow = sheet.createRow(5);
Cell targetCell = targetRow.getCell(5); if (targetCell==null) targetCell = targetRow.createCell(5);
if (sourceCell.getCellType() == CellType.NUMERIC && DateUtil.isCellDateFormatted(sourceCell)) {
System.out.println(sourceCell.getNumericCellValue()); // 8*1/24 = 1/3
System.out.println(sourceCell.getLocalDateTimeCellValue()); // 1899-12-31T08:00
//targetCell.setCellValue(sourceCell.getLocalDateTimeCellValue()); // does not work because sourceCell.getLocalDateTimeCellValue() is in year 1899
targetCell.setCellValue(sourceCell.getNumericCellValue());
targetCell.setCellStyle(sourceCell.getCellStyle());
}
FileOutputStream out = new FileOutputStream(filePath);
workbook.write(out);
out.close();
workbook.close();
}
}