<dependency>
        <groupId>org.icepdf.os</groupId>
        <artifactId>icepdf-core</artifactId>
        <version>6.1.2</version>
</dependency>

import org.icepdf.core.pobjects.Document;
import org.icepdf.core.pobjects.Page;
import org.icepdf.core.util.GraphicsRenderingHints;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

public class PDFToImageUtil {

    /*获取pdf文件名*/
    public String getPDFName(String filePath){
        File fileOrigin = new File(filePath);
        String fileName = fileOrigin.getName();
        fileName = fileName.substring(0,fileName.lastIndexOf("."));
        return fileName;
    }
    /*pdf转图片*/
    public List<String> Pdf2Img(String filePath,String imagePath) throws Exception {
        String fileName = getPDFName(filePath);
        File dir = new File(imagePath);
        if(!dir.exists()){
            boolean b = dir.mkdir();
            if(!b){
                return null;
            }
        }
        Document document = new Document();
        document.setFile(filePath);
        float scale = 2.5f;//缩放比例
        float rotation = 0f;//旋转角度
        List<String> filePaths = new ArrayList<String>();
        for(int i = 0; i<document.getNumberOfPages();i++){
            BufferedImage bufferedImage = (BufferedImage) document.getPageImage(i, GraphicsRenderingHints.SCREEN, Page.BOUNDARY_CROPBOX,rotation,scale);
            try {
                File file = new File(imagePath+"/"+fileName+new Date().getTime() +".png");
                filePaths.add(file.getPath());
                ImageIO.write(bufferedImage,"png",file);
            }catch (IOException e){
                e.printStackTrace();
            }
            bufferedImage.flush();
        }
        document.dispose();
        return  filePaths;
    }
}

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.List;

import javax.imageio.ImageIO;


public class PDFToMergeImageUtil {
    public String Pdf2MergeImg(String filePath,String imagePath) throws Exception {
        PDFToImageUtil pdfToImageUtil = new PDFToImageUtil();
        List<String> filePaths = pdfToImageUtil.Pdf2Img(filePath, imagePath);
        String fileName = pdfToImageUtil.getPDFName(filePath);
        BufferedImage destImage = null;
        for(int i =0 ; i < filePaths.size() - 1;i++){
            BufferedImage img1 = null;
            BufferedImage img2 = null;
            if(i == 0){
                img1 = getBufferedImage(filePaths.get(i));
                img2 = getBufferedImage(filePaths.get(i+1));
            }else{
                img1 = destImage;
                img2 = getBufferedImage(filePaths.get(i+1));
            }

            // 从图片中读取RGB
            int[] imageArrayOne = new int[img1.getWidth() * img1.getHeight()];
            imageArrayOne = img1.getRGB(0, 0, img1.getWidth(), img1.getHeight(), imageArrayOne, 0, img1.getWidth()); // 逐行扫描图像中各个像素的RGB到数组中
            int[] imageArrayTwo = new int[img2.getWidth() * img2.getHeight()];
            imageArrayTwo = img2.getRGB(0, 0, img2.getWidth(), img2.getHeight(), imageArrayTwo, 0, img2.getWidth());
            destImage = new BufferedImage(img1.getWidth(), img1.getHeight()+img2.getHeight(), BufferedImage.TYPE_INT_RGB);
            destImage.setRGB(0, 0, img1.getWidth(), img1.getHeight(), imageArrayOne, 0, img1.getWidth()); // 设置上半部分或左半部分的RGB
            destImage.setRGB(0, img1.getHeight(), img2.getWidth(), img2.getHeight(), imageArrayTwo, 0, img2.getWidth()); // 设置下半部分的RGB
        }
        File fileAll = new File(imagePath+"/"+fileName+".jpg");
        ImageIO.write(destImage,"png",fileAll);
        destImage.flush();
        return  fileAll.getPath();
    }
    /**
     * @param fileUrl
     *            文件绝对路径或相对路径

     * @return 读取到的缓存图像
     * @throws IOException
     *             路径错误或者不存在该文件时抛出IO异常
     */
    private BufferedImage getBufferedImage(String fileUrl)
            throws IOException {
        File f = new File(fileUrl);
        return ImageIO.read(f);
    }
}

import org.jeecg.business.utils.PDFToMergeImageUtil;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;
import java.io.IOException;
import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
public class Pdf2Image {

    @Value(value = "${path.imagePath}")
    private String imagePath;
    @Test
    public void test1() throws Exception {
        PDFToMergeImageUtil pdf = new PDFToMergeImageUtil();
        String listImg = pdf.Pdf2MergeImg("D://java//maven.pdf",imagePath);
        System.out.println(listImg);
    }
}