如何将一个pdf文件转换为一个大图片呢?

多页pdf转大图片的实现思路

1.加载pdf文件
2.限制最大页数，禁止大于10页
3.读取pdf 到buffer中
4.输出图片

注意事项:
    由于图片有最大像素限制，所以笔者限制为只转换10页的数据

package com.jd;

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.rendering.ImageType;
import org.apache.pdfbox.rendering.PDFRenderer;

import javax.imageio.ImageIO;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

/**
 * java265.com
 *  将PDF转换为一张大图片，避免OOM问题
 * author: Adeal
 */
public class PdfToJpgConverter {

    public static void main(String[] args) {
        String pdfPath = "D:/tmp/test.pdf";
        String outputFilePath = "D:/tmp/tmp/combined.jpg";

        try (PDDocument document = PDDocument.load(new File(pdfPath))) {
            PDFRenderer pdfRenderer = new PDFRenderer(document);
            int numberOfPages = document.getNumberOfPages();

            System.out.println("总页数：" + numberOfPages);
            if(numberOfPages >10){
                numberOfPages =10;
            }


            // 计算总高度和最大宽度
            int totalHeight = 0;
            int maxWidth = 0;
            for (int pageIndex = 0; pageIndex < numberOfPages; pageIndex++) {
                BufferedImage bim = pdfRenderer.renderImageWithDPI(pageIndex, 150, ImageType.RGB); // 降低分辨率
                totalHeight += bim.getHeight();
                maxWidth = Math.max(maxWidth, bim.getWidth());
            }

            // 创建一个大图片
            BufferedImage combinedImage = new BufferedImage(maxWidth, totalHeight, BufferedImage.TYPE_INT_RGB);
            Graphics2D g2d = combinedImage.createGraphics();

            // 分批处理页面
            int batchSize = 10; // 每次处理10页
            int yPosition = 0;
            for (int batchStart = 0; batchStart < numberOfPages; batchStart += batchSize) {
                int batchEnd = Math.min(batchStart + batchSize, numberOfPages);
                for (int pageIndex = batchStart; pageIndex < batchEnd; pageIndex++) {
                    BufferedImage bim = pdfRenderer.renderImageWithDPI(pageIndex, 150, ImageType.RGB); // 降低分辨率
                    g2d.drawImage(bim, 0, yPosition, null);
                    yPosition += bim.getHeight();
                    bim.flush(); //释放图像资源
                }
            }

            // 释放资源
            g2d.dispose();

            // 保存为JPG文件
            File outputFile = new File(outputFilePath);
            ImageIO.write(combinedImage, "jpg", outputFile);

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}