// i wrote a sample code to create xlsx format file, but it is not working properly at line number 19

private void write2007(File file) throws FileNotFoundException, IOException {
        XSSFWorkbook workbook = new XSSFWorkbook();
        if (sheetName.isEmpty()) {
            sheetName = "Sheet 1";
        }
        XSSFSheet sheet = workbook.createSheet(sheetName);
        XSSFRow headRow = sheet.createRow(0);
        // Write Head
        for (int i = 0; i < tableModel.getColumnCount(); i++) {
            XSSFCell cell = headRow.createCell(i);
            cell.setCellType(HSSFCell.CELL_TYPE_STRING);
            cell.setCellValue(tableModel.getColumnName(i));
            //Cell Style
            XSSFCellStyle cellStyle = workbook.createCellStyle();
            cellStyle.setAlignment(HorizontalAlignment.CENTER);
	    // bug code, unable to change the background color of cell
            cellStyle.setFillBackgroundColor(new XSSFColor(Color.LIGHT_GRAY));
            XSSFFont font = workbook.createFont();
            font.setBoldweight(XSSFFont.BOLDWEIGHT_BOLD);
            cellStyle.setFont(font);
            cell.setCellStyle(cellStyle);
        }
        //Write Data
        for (int i = 0; i < tableModel.getRowCount(); i++) {
            XSSFRow row = sheet.createRow(i + 1);
            for (int j = 0; j < tableModel.getColumnCount(); j++) {
                XSSFCell cell = row.createCell(j);
                String cellVal = null;
                try {
                    cellVal = tableModel.getValueAt(i, j).toString();
                } catch (NullPointerException ex) {
                    cellVal = "";
                }
                try {
                    float parseFloat = Float.parseFloat(cellVal);
                    cell.setCellType(Cell.CELL_TYPE_NUMERIC);
                    cell.setCellValue(parseFloat);
                } catch (NumberFormatException ex) {
                    cell.setCellType(Cell.CELL_TYPE_STRING);
                    cell.setCellValue(cellVal);
                }
            }
        }
        for (int i = 0; i < tableModel.getColumnCount(); i++) {
            sheet.autoSizeColumn(i);
        }
        FileOutputStream fos = new FileOutputStream(file);
        workbook.write(fos);
        fos.close();
    }