Creating the border for the merged cells in POI

Question

Could anyone explain me how to create the borders for the merged cells using Apache POI?
The Code I'm using is only affecting one cell.

sheet.addMergedRegion(new CellRangeAddress(1, 1, 2, 3));
Cell monthCell = subheaderRow.createCell(2);
monthCell.setCellValue(2);
monthCell.setCellStyle(styles.get("month"));



style = wb.createCellStyle();

style.setBorderBottom(CellStyle.BORDER_THIN);
style.setBorderTop(CellStyle.BORDER_THIN);
style.setBorderLeft(CellStyle.BORDER_THIN);
style.setBorderRight(CellStyle.BORDER_THIN);
style.setAlignment(CellStyle.ALIGN_CENTER);
style.setAlignment(CellStyle.ALIGN_CENTER);
style.setVerticalAlignment(CellStyle.VERTICAL_CENTER);
// style.setFillForegroundColor(IndexedColors.DARK_BLUE.getIndex());
// style.setFillPattern(CellStyle.SOLID_FOREGROUND);
// style.setFont(monthFont);
styles.put("month", style);

Answer 1

This can be done as below:

public void doMerge(int rowIndex, int columnIndex, int rowSpan, int columnSpan) {
    Cell cell = sheet.getRow(rowIndex).getCell(columnIndex);
    CellRangeAddress range = new CellRangeAddress(rowIndex, rowIndex + rowSpan - 1, columnIndex, columnIndex
            + columnSpan - 1);

    sheet.addMergedRegion(range);

    RegionUtil.setBorderBottom(cell.getCellStyle().getBorderBottom(), range, sheet, sheet.getWorkbook());
    RegionUtil.setBorderTop(cell.getCellStyle().getBorderTop(), range, sheet, sheet.getWorkbook());
    RegionUtil.setBorderLeft(cell.getCellStyle().getBorderLeft(), range, sheet, sheet.getWorkbook());
    RegionUtil.setBorderRight(cell.getCellStyle().getBorderRight(), range, sheet, sheet.getWorkbook());

    RegionUtil.setBottomBorderColor(cell.getCellStyle().getBottomBorderColor(), range, sheet, sheet.getWorkbook());
    RegionUtil.setTopBorderColor(cell.getCellStyle().getTopBorderColor(), range, sheet, sheet.getWorkbook());
    RegionUtil.setLeftBorderColor(cell.getCellStyle().getLeftBorderColor(), range, sheet, sheet.getWorkbook());
    RegionUtil.setRightBorderColor(cell.getCellStyle().getRightBorderColor(), range, sheet, sheet.getWorkbook());
}