Apache POI 是一个用于处理 Microsoft Office 文件的 Java 库。它可以用来创建、读取和修改 Excel 文件。在 Excel 文件中添加水印是一种常见的需求，但在 Excel 和 LibreOffice 中生成的外观有时会不同。以下是一个示例代码，演示如何在 Apache POI 中添加水印并处理不同的外观。

import org.apache.poi.hssf.usermodel.HSSFWorkbook;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.util.IOUtils;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;

public class WatermarkExample {
    public static void main(String[] args) throws Exception {
        // 从文件读取模板
        InputStream inputStream = new FileInputStream("template.xls");
        Workbook workbook = new HSSFWorkbook(inputStream);

        // 创建样式
        Font font = workbook.createFont();
        font.setColor(IndexedColors.GREY_50_PERCENT.getIndex());
        font.setFontHeightInPoints((short) 100);
        font.setBold(true);

        CellStyle style = workbook.createCellStyle();
        style.setFont(font);
        style.setRotation((short) -45);

        // 创建水印
        Drawing drawing = workbook.getSheetAt(0).createDrawingPatriarch();
        CreationHelper helper = workbook.getCreationHelper();

        ClientAnchor anchor = helper.createClientAnchor();
        anchor.setAnchorType(ClientAnchor.AnchorType.MOVE_AND_RESIZE);
        anchor.setCol1(5);
        anchor.setRow1(5);
        anchor.setCol2(10);
        anchor.setRow2(10);

        Picture pic = helper.createPicture(anchor, loadWatermarkImage(workbook));
        pic.resize();
        pic.setLineStyle((short) 0);
        pic.setLineWidth(0);
        pic.setPictureFormat(PictureFormat.JPEG);

        // 设置水印样式
        for (Sheet sheet : workbook) {
            Header header = sheet.getHeader();
            header.setCenter("&" + Drawing.SHAPE + "0");

            for (int i = 0; i < 100; i++) {
                Row row = sheet.createRow(i);
                Cell cell = row.createCell