EasyExcel：如何巧妙利用背景图片为Excel添加水印

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发布于 2025-08-14 15:27:14

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文章被收录于专栏：nobodynobody

在日常办公中，有时我们需要为Excel文件添加水印以表明文件状态，如“草稿”“机密”等。但Excel本身并没有直接添加水印的功能，常见的做法是插入图片，不过还有一种更高效的方法——将图片设置为工作表背景。今天就来揭秘如何利用EasyExcel结合POI技术实现这一操作。

创建水印图片

要设置背景图片作为水印，首先需生成合适的水印图片。我们使用Java的图形处理类来创建一张带有倾斜文字的透明图片。代码中，我们设置了图片的宽度、高度、字体样式、颜色及透明度，并将文字旋转一定角度以达到倾斜效果。


import com.alibaba.excel.write.handler.SheetWriteHandler;
import com.alibaba.excel.write.metadata.holder.WriteSheetHolder;
import com.alibaba.excel.write.metadata.holder.WriteWorkbookHolder;
import lombok.SneakyThrows;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.Color;
import java.awt.Font;
import java.awt.font.FontRenderContext;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

publicclass WatermarkWriteHandler implements SheetWriteHandler {
    privatefinal String waterMarkContent;

    public WatermarkWriteHandler(String waterMarkContent) {
        this.waterMarkContent = waterMarkContent;
    }

    

    public static ByteArrayOutputStream createWaterMark(String content) throws IOException {
        int width = 200;
        int height = 150;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 获取bufferedImage对象
        String fontType = "微软雅黑";
        int fontStyle = Font.BOLD;
        int fontSize = 20;
        Font font = new Font(fontType, fontStyle, fontSize);
        Graphics2D g2d = image.createGraphics(); // 获取Graphics2d对象
        image = g2d.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);
        g2d.dispose();
        g2d = image.createGraphics();
        g2d.setColor(new Color(0, 0, 0, 20)); //设置字体颜色和透明度，最后一个参数为透明度
        g2d.setStroke(new BasicStroke(1)); // 设置字体
        g2d.setFont(font); // 设置字体类型  加粗 大小
        g2d.rotate(-0.5, (double) image.getWidth() / 2, (double) image.getHeight() / 2);//设置倾斜度
        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;
        // 写入水印文字原定高度过小，所以累计写水印，增加高度
        g2d.drawString(content, (int) x, (int) baseY);
        // 设置透明度
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));
        // 释放对象
        g2d.dispose();
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(image, "png", os);
        return os;
    }



}

设置背景图片为水印

有了水印图片后，我们需要将其设置为Excel工作表的背景图片。在POI中，可以通过XSSFWorkbook和XSSFSheet对象来实现。


 /**
     * 为Excel打上水印工具函数
     *
     * @param sheet excel sheet
     * @param bytes 水印图片字节数组
     */
    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);
    }

WatermarkWriteHandler类整体实现如下：


import com.alibaba.excel.write.handler.SheetWriteHandler;
import com.alibaba.excel.write.metadata.holder.WriteSheetHolder;
import com.alibaba.excel.write.metadata.holder.WriteWorkbookHolder;
import lombok.SneakyThrows;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.xssf.usermodel.*;

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.Color;
import java.awt.Font;
import java.awt.font.FontRenderContext;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;

publicclass WatermarkWriteHandler implements SheetWriteHandler {
    privatefinal String waterMarkContent;

    public WatermarkWriteHandler(String waterMarkContent) {
        this.waterMarkContent = waterMarkContent;
    }

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

    public static ByteArrayOutputStream createWaterMark(String content) throws IOException {
        int width = 200;
        int height = 150;
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);// 获取bufferedImage对象
        String fontType = "微软雅黑";
        int fontStyle = Font.BOLD;
        int fontSize = 20;
        Font font = new Font(fontType, fontStyle, fontSize);
        Graphics2D g2d = image.createGraphics(); // 获取Graphics2d对象
        image = g2d.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);
        g2d.dispose();
        g2d = image.createGraphics();
        g2d.setColor(new Color(0, 0, 0, 20)); //设置字体颜色和透明度，最后一个参数为透明度
        g2d.setStroke(new BasicStroke(1)); // 设置字体
        g2d.setFont(font); // 设置字体类型  加粗 大小
        g2d.rotate(-0.5, (double) image.getWidth() / 2, (double) image.getHeight() / 2);//设置倾斜度
        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;
        // 写入水印文字原定高度过小，所以累计写水印，增加高度
        g2d.drawString(content, (int) x, (int) baseY);
        // 设置透明度
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));
        // 释放对象
        g2d.dispose();
        ByteArrayOutputStream os = new ByteArrayOutputStream();
        ImageIO.write(image, "png", os);
        return os;
    }

    /**
     * 为Excel打上水印工具函数
     *
     * @param sheet excel sheet
     * @param bytes 水印图片字节数组
     */
    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);
    }

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

}

使用EasyExcel导出带水印的Excel

在实际使用中，若使用EasyExcel进行Excel文件导出，可以通过实现SheetWriteHandler接口，并重写afterSheetCreate方法，来在创建工作表后添加水印。需注意，EasyExcel默认使用SXSSFWorkbook，要设置inMemory(true)才能使用XSSFWorkbook。


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

示例代码如下：

public static void main(String[] args) {
        try (ExcelWriter excelWriter = EasyExcel.write("/Users/logs/a.xlsx")
                .inMemory(true)//必须设置，以便使用XSSFWorkbook而非SXSSFWorkbook
                .registerWriteHandler(new WatermarkWriteHandler("认知科技技术团队"))
                .build()) {
            WriteSheet writeSheet1 = EasyExcel.writerSheet(0, "统计").head(Demo.class).build();
            WriteSheet writeSheet2 = EasyExcel.writerSheet(1, "分数据").head(Demo.class).build();
            WriteSheet writeSheet3 = EasyExcel.writerSheet(2, "分数据2").head(Demo.class).build();
            excelWriter.write(Arrays.asList(), writeSheet1);
            excelWriter.write(Arrays.asList(), writeSheet2);
            excelWriter.write(Arrays.asList(), writeSheet3);
        }
    }

水印效果如图：

使用POI单独设置水印

若不使用EasyExcel，仅使用POI来创建Excel文件并添加水印，可参考以下代码：

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);
        String rID = sheet.addRelation(null, XSSFRelation.IMAGES, workbook.getAllPictures().get(pictureIdx))
                .getRelationship().getId();
        sheet.getCTWorksheet().addNewPicture().setId(rID);
        workbook.write(fileOutputStream);
    }
}

以上方法，巧妙地利用了Excel工作表背景图片的特性，实现了类似水印的效果。该方案不仅适用于EasyExcel，也可用于其他基于POI的Excel操作场景。虽有内存消耗较大等局限，但在一些特定场景下，不失为一种实用的解决方案。

附：依赖

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>easyexcel-core</artifactId>
            <version>3.2.1</version>
        </dependency>
        <dependency>
            <groupId>org.apache.poi</groupId>
            <artifactId>ooxml-schemas</artifactId>
            <version>1.4</version>
        </dependency>

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原始发表：2025-08-14，如有侵权请联系 cloudcommunity@tencent.com 删除

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