1、下载一个 PDFRenderer.jar的包
2、相关代码
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.channels.FileChannel;

import javax.imageio.ImageIO;

import com.sun.pdfview.PDFFile;
import com.sun.pdfview.PDFPage;

public class PdfToJpgUtil
{
    public static int convertPdfToJpg(String srcFile, String tarFile,
            String tarPath)
    {
        int pageCnt = 0;
        try
        {
            // 加载PDF文件
            File file = new File(srcFile);
            RandomAccessFile raf = new RandomAccessFile(file, "r");
            FileChannel channel = raf.getChannel();
            ByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY, 0,
                    channel.size());
            PDFFile pdffile = new PDFFile(buf);

            pageCnt = pdffile.getNumPages();

            for (int i = 1; i <= pdffile.getNumPages(); i++)
            {
                PDFPage page = pdffile.getPage(i);

                Rectangle rect = new Rectangle(0, 0, (int) page.getBBox()
                        .getWidth(), (int) page.getBBox().getHeight());
                int width = 1700;
                int height = rect.height * 1700 / rect.width;
                Image img = page
                        .getImage(width, height, rect, null, true, true);

                BufferedImage tag = new BufferedImage(width, height,
                        BufferedImage.TYPE_INT_RGB);
                tag.getGraphics().drawImage(img, 0, 0, width, height, null);
                String path = tarPath + "detail/" + i + ".jpg";
                // 输出到文件流
                FileOutputStream out = new FileOutputStream(path);
                ImageIO.write(tag, "jpg", out);
                out.close();
                raf.close();
            }
        }
        catch(IOException e)
        {
            e.printStackTrace();
        }

        return pageCnt;
    }

    public static void convertPdfToJpg(String srcFile, String tarPath)
    {
        RandomAccessFile raf=null;
        try
        {
            // 加载PDF文件
            File file = new File(srcFile);
            raf = new RandomAccessFile(file, "r");
            FileChannel channel = raf.getChannel();
            ByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY, 0,
                    channel.size());
            PDFFile pdffile = new PDFFile(buf);
            if (pdffile.getNumPages() > 0)
            {
                PDFPage page = pdffile.getPage(1);

                Rectangle rect = new Rectangle(0, 0, (int) page.getBBox()
                        .getWidth(), (int) page.getBBox().getHeight());
                int width = rect.width;
                int height = rect.height;
                Image img = page
                        .getImage(width, height, rect, null, true, true);

                BufferedImage tag = new BufferedImage(width, height,
                        BufferedImage.TYPE_INT_RGB);
                tag.getGraphics().drawImage(img, 0, 0, width, height, null);
                FileOutputStream out = new FileOutputStream(tarPath); // 输出到文件流
                ImageIO.write(tag, "jpg", out);
                out.close();
               
            }
        }
        catch(Exception e)
        {
            e.printStackTrace();
        }finally{
            if(raf!=null){
                try {
                    raf.close();
                }
                catch(IOException e) {
                    e.printStackTrace();
                }
            }
        }

    }
}