java使用Spire，实现对已经存在的Excel插入一张图片，并使其在单元格中居中

好的，针对您的问题，我可以给您提供以下Java代码示例，使用Spire插入一张图片并居中显示在单元格中：

import com.spire.xls.*;
import com.spire.xls.core.SheetViewBase;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;

public class InsertImageInExcel {

    public static void main(String[] args) throws Exception {

        //加载Excel文档
        Workbook workbook = new Workbook();
        workbook.loadFromFile("ExistingExcel.xlsx");

        //获取第一个工作表
        Worksheet sheet = workbook.getWorksheets().get(0);

        //加载图片
        BufferedImage image = ImageIO.read(new File("Image.jpg"));

        //将图片插入到单元格中
        int rowIndex = 1;
        int columnIndex = 1;
        sheet.getPictures().insert(image, rowIndex, columnIndex);

        //设置图片所在单元格居中显示
        Picture picture = sheet.getPictures().get(0);
        CellRange range = sheet.getCellRange(picture.getTopRow(), picture.getLeftColumn());
        setPictureCenter(range, picture);

        //保存Excel文档
        workbook.saveToFile("ExistingExcelWithImage.xlsx", ExcelVersion.Version2010);
    }
    
    //将图片居中显示在单元格中
    public static void setPictureCenter(CellRange range, Picture picture) {
        SheetViewBase view = range.getSheetView();
        Rectangle rect = view.getCellRectangle(range.getRow(), range.getColumn());
        int cellWidth = rect.width;
        int cellHeight = rect.height;
        int imageWidth = picture.getWidth();
        int imageHeight = picture.getHeight();
        int x = rect.x + (cellWidth - imageWidth) / 2;
        int y = rect.y + (cellHeight - imageHeight) / 2;
        picture.setTopLeftColumn(x);
        picture.setTopLeftRow(y);
    }
}

您需要将代码中的 "ExistingExcel.xlsx" 和 "Image.jpg" 替换为您自己的Excel文档和图片路径。此外，您还可以根据需要调整图片在单元格中的位置和大小。