XSSFRow pre = sheet.createRow(0);
		
	XSSFCell titleCell = pre.createCell(0);
	titleCell.setCellType(CellType.STRING);
	titleCell.setCellValue("Sent Email Detailed Statistics");
	XSSFFont font = workbook.createFont();
	font.setFontHeightInPoints((short) 25);
	XSSFCellStyle titleStyle = workbook.createCellStyle();
	XSSFColor grey = new XSSFColor(new java.awt.Color(255,195,1));
	titleStyle.setFillBackgroundColor(grey);
	//titleStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND);
	titleStyle.setFont(font);
	titleStyle.setAlignment(HorizontalAlignment.CENTER);
	titleStyle.setWrapText(true);
	titleCell.setCellStyle(titleStyle);

	XSSFCell desCell = pre.createCell(2);
	desCell.setCellType(CellType.STRING);
	desCell.setCellValue("Details statistics for each email which is already sent.");
	XSSFFont desFont = workbook.createFont();
	desFont.setItalic(true);
	XSSFCellStyle desStyle = workbook.createCellStyle();
	desStyle.setFont(desFont);
	titleStyle.setWrapText(true);
	desCell.setCellStyle(desStyle);
		
    //merge cell
	int firstRow = 0;
	int lastRow = 0;
	int firstCol = 0;
	int lastCol = 1;
	sheet.addMergedRegion(new CellRangeAddress(firstRow, lastRow, firstCol, lastCol));
		
    //auto size columns include merged cell.
	sheet.autoSizeColumn(0, true);
	sheet.autoSizeColumn(1, true);
	sheet.autoSizeColumn(3, true);
	sheet.autoSizeColumn(4, true);

	XSSFRow headerRow = sheet.createRow(1);

	int i = 0;
	for (String headerCell : header) {
		XSSFCell cell = headerRow.createCell(i);
		cell.setCellType(CellType.STRING);
		cell.setCellValue(headerCell);
		sheet.autoSizeColumn(i, true);
		cell.setCellStyle(style);
		i++;
	}