Develop Reference

Apache POI - issue with cell background color

I want to color an Excel cell with blue color :
HSSFCellStyle headerCellStyle = worksheet.getWorkbook().createCellStyle();
headerCellStyle.setFillBackgroundColor(HSSFColor.BLUE.index);
headerCellStyle.setFillPattern(CellStyle.FINE_DOTS);
cell = rowHeader.createCell(startColIndex++);
cell.setCellValue("Titre");
cell.setCellStyle(headerCellStyle);
The cell should be blue instead of grey. I don't understant what I am doing wrong.

Excel Sheet with existing Date style not working

Need to fill data in Excel template , whcih has Date format style applied to cells. Somehow Date format is not reflecting after filling data in excel cell.
if (cellVal instanceof Date || cellVal instanceof Timestamp) {
cell.setCellValue("20-08-2019"));
CellStyle style = cell.getCellStyle();
cell.setCellStyle(style);
}
Here cell.getCellStyle() to get existing cell style from excel template which should convert date in this format: "20-AUG-19"
issue is even after appying this style cell.setCellStyle(style), Date values style remained same i.e. "20-08-2019"

CellStyle style = cell.getCellStyle();
cell.setCellStyle(style);
you are getting the style of cell variable and setting it again to cell so you're not changing anything at all.
your code should be like that:
CellStyle style = cellVal.getCellStyle(); //cellVal instead of cell
cell.setCellStyle(style);

SXSSF can't create Font and DateFormat

Question
In a SXSSF Workbook:
How can I set font?
How can I set celltype to date?
Context
I need to write an excel .xlsx file with a huge amount of rows and columns (400.000 rows, 50 fields each) so I'm using apache poi, SXSSF workbook. I created a test file with this amount of dummy text and it works but I want cells to have a custom font: so if text is somehow representing time cell type should be set to "date" (allowing me to filter rows by date easily).
I wrote a function which allows me to create a cell, check and modify its text type (currency, string, data) based on textType value that I pass to the function. Text type is correctly recognized as I examine data. Currency and text are correctly modified but when I tried to set Font and Data type it doesn't work at all.
(I already have a working function (XSSF) which creates an excel with custom font and different data types included "date", it just can't generate large excel files due to GC overhead, that's why I had to switch to SXSSF)
Error
I get this kind of compile error.
Errors incompatible types;found :
org.apache.poi.ss.usermodel.Font,required:
org.apache.poi.xssf.usermodel.XSSFFont at line 235 (235:40)
incompatible types;found :
org.apache.poi.ss.usermodel.DataFormat,required:
org.apache.poi.xssf.usermodel.XSSFDataFormat at line 271 (271:54)
incompatible types;found :
org.apache.poi.ss.usermodel.DataFormat,required:
org.apache.poi.xssf.usermodel.XSSFDataFormat at line 308 (308:54)
incompatible types;found :
org.apache.poi.ss.usermodel.DataFormat,required:
org.apache.poi.xssf.usermodel.XSSFDataFormat at line 335 (335:54)
incompatible types;found :
org.apache.poi.ss.usermodel.DataFormat,required:
org.apache.poi.xssf.usermodel.XSSFDataFormat at line 375 (375:66)
Since SXSSFFont doesn't exists, I tried to fix it by creating a Font object and then using it instead of XSSFFont.
Same for DataFormat.
But I still find types issues here and there in code.
XSSFFont font = (XSSFFont) workbook.createFont();
XSSFDataFormat df = (XSSFFont) workbook.createDataFormat();
Also tried code above but it doesnt work, I get
ClassCastException error
Code
//[...]
SXSSFWorkbook workbook = new SXSSFWorkbook(100);
Sheet sheet;
Row row;
Cell cell;
//[...]
XSSFFont font = workbook.createFont();
font.setBold(fontBold);
font.setItalic(fontItalic);
font.setFontHeightInPoints( (short) fontSize);
if (!fontUnderline) {
font.setUnderline(FontUnderline.NONE);
}
else {
font.setUnderline(FontUnderline.SINGLE);
}
font.setColor(fontColor);
CellStyle style = workbook.createCellStyle();
style.setFont(font);
//[...]
if (textType == 'T') {
XSSFDataFormat df = workbook.createDataFormat();
style.setDataFormat(df.getFormat("d-mmm-yyyy hh:mi:ss"));
Calendar c = Calendar.getInstance();
c.set(year, month, day, hour, minute,second);
cell.setCellValue(c.getTime());
}
//in the end I set cell value and style
cell.setCellStyle(style);
cell.setCellValue(text);

Here I created a short example using a SXSSFWorkbook and filling 1 cell with a date and applying the proper format as well as a font.
SXSSFWorkbook s = new SXSSFWorkbook();
Font font = s.createFont();
font.setBold(true);
font.setItalic(true);
short dateStyle = s.createDataFormat().getFormat("mm/dd/yy;#");
CellStyle dateCellFormat = s.createCellStyle();
dateCellFormat.setDataFormat(dateStyle);
dateCellFormat.setFont(font);
SXSSFSheet sheet = s.createSheet("Test");
Row r = sheet.createRow(0);
Cell c = r.createCell(0);
c.setCellValue(new Date());
c.setCellStyle(dateCellFormat);
s.write(Files.newOutputStream(Paths.get("D:/test.xlsx"), StandardOpenOption.CREATE_NEW));
s.close();
You will have to make some adjustments, but I hope you get the idea (use the appropriate Interface's)

Applying specific cell data format using POI

I need to apply specific data format to cell.
XSSFCellStyle cellStyle = workBook.createCellStyle();
XSSFDataFormat format = workBook.createDataFormat();
cellStyle.setDataFormat(format.getFormat("m/d/yy h:mm"));
dataCell.setCellType(1); //String
dataCell.setCellStyle(cellStyle);
The data is being written but the problem is that the format is applied only when I open excel sheet (in Excel application), click inside the cell with my data.
And then pressing Enter key.
Only then the format is applied.
How can I apply the format without clicking on every cell?

Your problem is that you're setting the cell to be a string. For the most part, cell formatting rules only apply to numeric cells. They don't apply to string cells, those don't get formatted (as they're already formatted to a string!)
XSSFCellStyle cellStyle = workBook.createCellStyle();
XSSFDataFormat format = workBook.createDataFormat();
cellStyle.setDataFormat(format.getFormat("m/d/yy h:mm"));
dataCell.setCellStyle(cellStyle);
// Set Cell Type not really needed, the setCellValue does it
dataCell.setCellType(Cell.CELL_TYPE_NUMERIC);
// Set a date value (2012-06-05 08:50)
dataCell.setCellValue(new Date(1338878999635));
When you open that in Excel, it ought to be have as expected

This is how you change the cell format to Date.
var workBook = new XSSFWorkbook();
var sheet = workBook.CreateSheet("Sheet1");
var dateStyle = workBook.CreateCellStyle();
var dataFormat = workBook.CreateDataFormat();
dateStyle.DataFormat = dataFormat.GetFormat("M/D/YYYY");
row.CreateCell(0).SetCellValue(item.ModifiedDate.HasValue ?
item.ModifiedDate.Value.ToShortDateString(): "");
row.Cells[0].CellStyle = dateStyle; // This will change your cell to date
format.

Why does org.apache.poi.hssf give wrong color with Excel 2007?

Why does org.apache.poi.hssf give the wrong color a cell which with Excel 2007? With the 2010 version there are no problem.
Any idea for a fix/workaround?
final HSSFCellStyle cellStyle = (HSSFCellStyle) cell.getCellStyle();
final HSSFColor backgroundColor = cellStyle.getFillForegroundColorColor();
String theColor = ExcelToHtmlUtils.getColor( backgroundColor );
I tried couple libraries but no luck. Only xlsgen gives good results but it is not open source, which I would prefer.

One thing that I notice: you seem to want the background color, but you instead ask for the FillForegroundColorColor. I think you want to do this instead:
final HSSFColor backgroundColor = cellStyle.getFillBackgroundColorColor();
Try that instead and let us know.