POI设置某一单元格的字体颜色等样式（踩坑记录）

for (Cell cell : redColorCellList) {
    CellStyle cellStyle = cell.getCellStyle();
    Font font = workbook.getFontAt(cellStyle.getFontIndexAsInt());
    font.setColor(IndexedColors.RED.getIndex());
    cellStyle.setFont(font);
    cell.setCellStyle(cellStyle);
}

// 新建 excel
Workbook workbook = new XSSFWorkbook();
// 新建一个 sheet
Sheet sheet = workbook.createSheet();

CellStyle cellStyle = workbook.createCellStyle();
cellStyle.setFillForegroundColor(IndexedColors.LIGHT_YELLOW.getIndex()); // 背景色: 浅黄色
cellStyle.setFillPattern(FillPatternType.SOLID_FOREGROUND); // 背景色填充样式：单色填充
cellStyle.setAlignment(HorizontalAlignment.CENTER); // 水平布局：居中
cellStyle.setVerticalAlignment(VerticalAlignment.CENTER);// 垂直布局：居中
cellStyle.setBorderBottom(BorderStyle.DOUBLE); // 双边框
cellStyle.setBorderLeft(BorderStyle.THIN);// 薄边框
cellStyle.setBorderRight(BorderStyle.DOUBLE); // 双边框
cellStyle.setBorderTop(BorderStyle.THIN);// 薄边框
cellStyle.setBottomBorderColor(IndexedColors.WHITE.getIndex()); // 下边框：白色
cellStyle.setRightBorderColor(IndexedColors.GREEN.getIndex()); // 右边框：绿色
cellStyle.setWrapText(true); // 文本自动换行

Font font = workbook.createFont();
font.setBold(false); // 加粗
font.setFontName("微软雅黑"); // 字体
font.setFontHeightInPoints((short) 14); // 字体高度
font.setColor(IndexedColors.BLACK.getIndex()); // 字体颜色：黑色
cellStyle.setFont(font);

for (int i = 0; i < 5 ; i++) {
    // 设置列宽
    sheet.setColumnWidth(i, 30 * 160);
    // 新增一行 row
    Row row = sheet.createRow(i);
    row.setHeightInPoints(40);
    for (int j = 0; j < 5; j++) {
        // 新增一个单元格 cell
        Cell cell = row.createCell(j);
        cell.setCellValue("Hello_" + i + j);
        cell.setCellStyle(cellStyle);
    }
}

FileOutputStream outputStream = new FileOutputStream("D:\\poi-excel-style-demo.xlsx");
workbook.write(outputStream);
outputStream.flush();
outputStream.close();
workbook.close();

// 设置第一行为红色，并加粗
CellStyle redCellStyle = null;
for (int m = 0; m < 5; m++) {
    Cell cell = sheet.getRow(0).getCell(m);
    if (redCellStyle == null) {
        redCellStyle = workbook.createCellStyle();
        // 重点：从现有样式克隆style，只修改Font，其它style不变
        redCellStyle.cloneStyleFrom(cell.getCellStyle());
        // 获取原有字体
        Font oldFont = workbook.getFontAt(redCellStyle.getFontIndexAsInt());
        // 创建新字体
        Font redFont = workbook.createFont();
        // 重点：保留原字体样式
        redFont.setFontName(oldFont.getFontName()); // 保留原字体
        redFont.setFontHeightInPoints(oldFont.getFontHeightInPoints()); // 保留原字体高度
        redFont.setBold(true); // 加粗
        redFont.setColor(IndexedColors.RED.getIndex());  // 字体颜色：红色
        // 设置红色字体
        redCellStyle.setFont(redFont);
    }
    // 设置样式
    cell.setCellStyle(redCellStyle);
}

public static void setCellFont(List<Cell> cellList, FontParam fontParam) {
        if (CollectionUtils.isEmpty(cellList) || fontParam == null) {
            return;
        }
        CellStyle cellStyle = null;
        for (Cell cell : cellList) {
            if (cellStyle == null) {
                Workbook workbook = cell.getSheet().getWorkbook();
                cellStyle = workbook.createCellStyle();
                // 从现有样式克隆style，只修改Font，其它style不变
                cellStyle.cloneStyleFrom(cell.getCellStyle());
                // 获取原有字体
                Font oldFont = workbook.getFontAt(cellStyle.getFontIndexAsInt());
                // 创建新字体
                Font newFont = workbook.createFont();
                newFont.setFontName(fontParam.getFontName() == null? oldFont.getFontName(): fontParam.getFontName());
                newFont.setFontHeightInPoints(fontParam.getFontHeightInPoints() == null? oldFont.getFontHeightInPoints(): fontParam.getFontHeightInPoints());
                newFont.setBold(fontParam.getBold() == null? oldFont.getBold(): fontParam.getBold());
                newFont.setItalic(fontParam.getItalic() == null? oldFont.getItalic(): fontParam.getItalic());
                newFont.setStrikeout(fontParam.getStrikeout() == null? oldFont.getStrikeout(): fontParam.getStrikeout());
                newFont.setUnderline(fontParam.getUnderline() == null? oldFont.getUnderline(): fontParam.getUnderline());
                newFont.setColor(fontParam.getColor() == null? oldFont.getColor(): fontParam.getColor());
                // 设置字体
                cellStyle.setFont(newFont);
            }
            // 设置样式
            cell.setCellStyle(cellStyle);
        }
    }

    /**
     * 字体参数类，为null代表不设置
     */
    @Data
    @Builder
    @NoArgsConstructor
    @AllArgsConstructor
    public static class FontParam {

        /**
         * 字体名
         */
        private String fontName;
        /**
         * 字体像素高度
         */
        private Short fontHeightInPoints;
        /**
         * 是否加粗
         */
        private Boolean bold;
        /**
         * 是否斜体
         */
        private Boolean italic;
        /**
         * 是否删除线
         */
        private Boolean strikeout;
        /**
         * 下划线类型
         * @see #U_NONE
         * @see #U_SINGLE
         * @see #U_DOUBLE
         * @see #U_SINGLE_ACCOUNTING
         * @see #U_DOUBLE_ACCOUNTING
         */
        private Byte underline;
        /**
         * 字体颜色
         */
        private Short color;

        /**
         * not underlined
         */
        public final static byte U_NONE = 0;

        /**
         * single (normal) underline
         */
        public final static byte U_SINGLE = 1;

        /**
         * double underlined
         */
        public final static byte U_DOUBLE = 2;

        /**
         * accounting style single underline
         */
        public final static byte U_SINGLE_ACCOUNTING = 0x21;

        /**
         * accounting style double underline
         */
        public final static byte U_DOUBLE_ACCOUNTING = 0x22;
    }