引言

本文添加水印通過java生成圖片，設(shè)置為excel背景圖片實(shí)現(xiàn)。不僅僅局限于EasyExcel,凡是采用POI實(shí)現(xiàn)都可以采用該方案，但唯一的局限在于必須使用POI中的XSSFWorkbook對象，也就是對應(yīng)Excel2007的版本，擴(kuò)展名是.xlsx，具體實(shí)現(xiàn)可查看以下代碼。

maven依賴

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>easyexcel</artifactId>
    <version>2.2.5</version>
</dependency>
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.12</version>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>org.apache.poi</groupId>
    <artifactId>ooxml-schemas</artifactId>
    <version>1.4</version>
</dependency>
<!-- springboot相關(guān)依賴自行添加 -->

代碼實(shí)現(xiàn)

主要思路還是通過easyexcel獲取XSSFSheet對象，可以實(shí)現(xiàn)SheetWriteHandler，重寫afterSheetCreate方法來實(shí)現(xiàn)設(shè)置背景。easyexcel默認(rèn)使用的SXSSFWorkbook(低內(nèi)存操作excel的方式)，設(shè)置inMemory(true)則會使用XSSFWorkbook構(gòu)造excel操作對象。
如果不是使用easyexcel框架，使用XSSFWorkbook對象來創(chuàng)建excel操作對象即可。

1.eaysexcel Handler編寫

/**
 * excel添加水印，只支持XSSFWorkbook，其余類別：SXSSFWorkbook、SXSSFWorkbook請另尋他法
 * easyExcel使用時需要設(shè)置inMemory(true)，否者默認(rèn)使用的是SXSSFWorkbook，會報錯！
 */
@RequiredArgsConstructor
public class WaterMarkHandler implements SheetWriteHandler {

    private final String WATER_MARK;

    public static ByteArrayOutputStream createWaterMark(String content) throws IOException {
        int width = 200;
        int height = 150;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 獲取bufferedImage對象
        String fontType = "微軟雅黑";
        int fontStyle = Font.BOLD;
        int fontSize = 20;
        Font font = new Font(fontType, fontStyle, fontSize);
        Graphics2D g2d = image.createGraphics(); // 獲取Graphics2d對象
        image = g2d.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);
        g2d.dispose();
        g2d = image.createGraphics();
        g2d.setColor(new Color(0, 0, 0, 20)); //設(shè)置字體顏色和透明度，最后一個參數(shù)為透明度
        g2d.setStroke(new BasicStroke(1)); // 設(shè)置字體
        g2d.setFont(font); // 設(shè)置字體類型  加粗 大小
        g2d.rotate(-0.5, (double) image.getWidth() / 2, (double) image.getHeight() / 2);//設(shè)置傾斜度
        FontRenderContext context = g2d.getFontRenderContext();
        Rectangle2D bounds = font.getStringBounds(content, context);
        double x = (width - bounds.getWidth()) / 2;
        double y = (height - bounds.getHeight()) / 2;
        double ascent = -bounds.getY();
        double baseY = y + ascent;
        // 寫入水印文字原定高度過小，所以累計寫水印，增加高度
        g2d.drawString(content, (int) x, (int) baseY);
        // 設(shè)置透明度
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));
        // 釋放對象
        g2d.dispose();
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(image, "png", os);
        return os;
    }


    /**
     * 為Excel打上水印工具函數(shù)
     *
     * @param sheet excel sheet
     * @param bytes 水印圖片字節(jié)數(shù)組
     */
    public static void putWaterRemarkToExcel(XSSFSheet sheet, byte[] bytes) {
        //add relation from sheet to the picture data
        XSSFWorkbook workbook = sheet.getWorkbook();
        int pictureIdx = workbook.addPicture(bytes, Workbook.PICTURE_TYPE_PNG);
        String rID = sheet.addRelation(null, XSSFRelation.IMAGES, workbook.getAllPictures().get(pictureIdx))
                .getRelationship().getId();
        //set background picture to sheet
        sheet.getCTWorksheet().addNewPicture().setId(rID);
    }

    @Override
    public void beforeSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
    }

    @SneakyThrows
    @Override
    public void afterSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
        try (ByteArrayOutputStream waterMark = createWaterMark(WATER_MARK)){
            XSSFSheet sheet = (XSSFSheet) writeSheetHolder.getSheet();
            putWaterRemarkToExcel(sheet, waterMark.toByteArray());
        }
    }
}

2.導(dǎo)出示例

@GetMapping("/export")
public void export(HttpServletResponse response) throws IOException {
    response.setContentType("application/vnd.ms-excel");
    response.setCharacterEncoding("utf-8");
    // 這里URLEncoder.encode可以防止中文亂碼 當(dāng)然和easyexcel沒有關(guān)系
    String fileName = URLEncoder.encode("導(dǎo)出測試", "UTF-8");
    response.setHeader("Content-disposition", "attachment;filename=" + fileName + ".xlsx");
    EasyExcel.write(response.getOutputStream(), DemoData.class)
                .inMemory(true) // 注意，此項(xiàng)配置不能少
                .registerWriteHandler(new WaterMarkHandler("我是水印"))
                .sheet("模板")
                .doWrite(data());
}


private List<DemoData> data() {
    List<DemoData> list = new ArrayList<DemoData>();
    for (int i = 0; i < 10; i++) {
        DemoData data = new DemoData();
        data.setString("字符串" + i);
        data.setDate(new Date());
        data.setDoubleData(0.56);
        list.add(data);
    }
    return list;
}


@Data
public class DemoData {
    @ExcelProperty("字符串標(biāo)題")
    private String string;
    @ExcelProperty("日期標(biāo)題")
    private Date date;
    @ExcelProperty("數(shù)字標(biāo)題")
    private Double doubleData;
    /**
     * 忽略這個字段
     */
    @ExcelIgnore
    private String ignore;
}

3.導(dǎo)出效果

效果

4.基于POI

public static void main(String[] args) throws IOException {
    FileOutputStream fileOutputStream = new FileOutputStream(new File("F:\\test.xlsx"));
    XSSFWorkbook workbook = new XSSFWorkbook();
    XSSFSheet sheet = workbook.createSheet("Sheet1");
    try (ByteArrayOutputStream byteArrayOutputStream = WaterMarkHandler.createWaterMark("我是水印")){
        int pictureIdx = workbook.addPicture(byteArrayOutputStream.toByteArray(), Workbook.PICTURE_TYPE_PNG);
        //add relation from sheet to the picture data
        String rID = sheet.addRelation(null, XSSFRelation.IMAGES, workbook.getAllPictures().get(pictureIdx))
                .getRelationship().getId();
        //set background picture to sheet
        sheet.getCTWorksheet().addNewPicture().setId(rID);
        workbook.write(fileOutputStream);
    }
}

如此以來也算是實(shí)現(xiàn)了水印的功能，比插入圖片的方式強(qiáng)多了。excel是沒有水印功能的，目前來看也就只有插入圖片和設(shè)置背景圖片兩種方式。
通過以上兩種方式對比，可以發(fā)現(xiàn)核心代碼就sheet.getCTWorksheet().addNewPicture().setId(rID);是設(shè)置背景的方法，在Sheet的幾個實(shí)現(xiàn)中，只有XSSFSheet支持，當(dāng)然使用XSSF來操作excel的唯一問題就是耗內(nèi)存，如果有更好的實(shí)現(xiàn)也請告知一下哈！