实现easyexcel中的SheetWriteHandler，在afterSheetCreate中添加水印

smart-admin-api/sa-admin/src/main/java/net/lab1024/sa/admin/util/excel/CustomWaterMarkHandler.java

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+package net.lab1024.sa.admin.util.excel;
+
+
+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.extern.slf4j.Slf4j;
+import org.apache.poi.openxml4j.opc.PackagePartName;
+import org.apache.poi.openxml4j.opc.PackageRelationship;
+import org.apache.poi.openxml4j.opc.TargetMode;
+import org.apache.poi.xssf.usermodel.XSSFPictureData;
+import org.apache.poi.xssf.usermodel.XSSFRelation;
+import org.apache.poi.xssf.usermodel.XSSFSheet;
+import org.apache.poi.xssf.usermodel.XSSFWorkbook;
+
+import javax.imageio.ImageIO;
+import java.awt.*;
+import java.awt.geom.AffineTransform;
+import java.awt.image.BufferedImage;
+import java.io.ByteArrayOutputStream;
+
+/**
+ *
+ * @author liuzhexian
+ * @since 2024-04-16
+ * @email 1037512352@qq.com
+ */
+@Slf4j
+public class CustomWaterMarkHandler implements SheetWriteHandler {
+
+    private final Watermark watermark;
+
+    public CustomWaterMarkHandler(Watermark watermark) {
+        this.watermark = watermark;
+    }
+
+    @Override
+    public void afterSheetCreate(WriteWorkbookHolder writeWorkbookHolder, WriteSheetHolder writeSheetHolder) {
+        BufferedImage bufferedImage = createWatermarkImage();
+        XSSFWorkbook workbook = (XSSFWorkbook) writeSheetHolder.getParentWriteWorkbookHolder().getWorkbook();
+        try {
+            // 添加水印的具体操作
+            addWatermarkToSheet(workbook, bufferedImage);
+        } catch (Exception e) {
+            log.error("添加水印出错:", e);
+        }
+
+    }
+
+    /**
+     * 创建水印图片
+     *
+     * @return
+     */
+    private BufferedImage createWatermarkImage() {
+        // 获取水印相关参数
+        Font font = watermark.getFont();
+        int width = watermark.getWidth();
+        int height = watermark.getHeight();
+        Color color = watermark.getColor();
+        String text = watermark.getContent();
+
+        // 创建带有透明背景的 BufferedImage
+        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
+        Graphics2D g = image.createGraphics();
+
+        // 设置画笔字体、平滑、颜色
+        g.setFont(font);
+        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
+        g.setColor(color);
+
+        // 计算水印位置和角度
+        int y = watermark.getYAxis();
+        int x = watermark.getXAxis();
+        AffineTransform transform = AffineTransform.getRotateInstance(Math.toRadians(-watermark.getAngle()), 0, y);
+        g.setTransform(transform);
+        // 绘制水印文字
+        g.drawString(text, x, y);
+
+        // 释放资源
+        g.dispose();
+
+        return image;
+    }
+
+    private void addWatermarkToSheet(XSSFWorkbook workbook, BufferedImage watermarkImage) {
+        try (ByteArrayOutputStream os = new ByteArrayOutputStream()) {
+            ImageIO.write(watermarkImage, "png", os);
+            int pictureIdx = workbook.addPicture(os.toByteArray(), XSSFWorkbook.PICTURE_TYPE_PNG);
+            XSSFPictureData pictureData = workbook.getAllPictures().get(pictureIdx);
+            for (int i = 0; i < workbook.getNumberOfSheets(); i++) {
+                // 获取每个Sheet表
+                XSSFSheet sheet = workbook.getSheetAt(i);
+                PackagePartName ppn = pictureData.getPackagePart().getPartName();
+                String relType = XSSFRelation.IMAGES.getRelation();
+                PackageRelationship pr = sheet.getPackagePart().addRelationship(ppn, TargetMode.INTERNAL, relType, null);
+                sheet.getCTWorksheet().addNewPicture().setId(pr.getId());
+            }
+        } catch (Exception e) {
+            // 处理ImageIO.write可能抛出的异常
+            log.error("添加水印图片时发生错误", e);
+        }
+    }
+}
+