利用pdfbox和itext包将pdf的url转换为图片

首先，需要下载并导入pdfbox和itext包。

然后，可以使用以下代码将pdf的url转换为图片：

import java.awt.image.BufferedImage;
import java.io.File;
import java.net.URL;
import javax.imageio.ImageIO;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.rendering.PDFRenderer;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.parser.PdfReaderContentParser;
import com.itextpdf.text.pdf.parser.RenderListener;
import com.itextpdf.text.pdf.parser.ImageRenderInfo;
import com.itextpdf.text.pdf.parser.PdfRenderListener;

public class PDFtoImageConverter {
    public static void convertUsingPDFBox(String pdfUrl, String imagePath) throws Exception {
        URL url = new URL(pdfUrl);
        PDDocument document = PDDocument.load(url.openStream());
        PDFRenderer pdfRenderer = new PDFRenderer(document);
        for (int page = 0; page < document.getNumberOfPages(); ++page) {
            BufferedImage img = pdfRenderer.renderImageWithDPI(page, 300);
            ImageIO.write(img, "PNG", new File(imagePath + "_" + (page + 1) + ".png"));
        }
        document.close();
    }

    public static void convertUsingIText(String pdfUrl, String imagePath) throws Exception {
        PdfReader reader = new PdfReader(new URL(pdfUrl));
        PdfReaderContentParser parser = new PdfReaderContentParser(reader);
        ImageRenderListener listener = new ImageRenderListener(new File(imagePath));
        for (int i = 1; i <= reader.getNumberOfPages(); i++) {
            parser.processContent(i, listener);
        }
        reader.close();
    }

    private static class ImageRenderListener implements RenderListener {
        private final String basePath;
        private int pageNumber;

        public ImageRenderListener(File outputFolder) {
            this.basePath = outputFolder.getAbsolutePath();
            this.pageNumber = 0;
        }

        @Override
        public void beginTextBlock() {}

        @Override
        public void renderText(TextRenderInfo renderInfo) {}

        @Override
        public void endTextBlock() {}

        @Override
        public void renderImage(ImageRenderInfo renderInfo) {
            try {
                ++pageNumber;
                String filename = String.format("%s_%d.png", basePath, pageNumber);
                renderInfo.getImage().getBufferedImage().flush();
                ImageIO.write(renderInfo.getImage().getBufferedImage(), "png", new File(filename));
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
    }
}

调用示例：

public class Main {
    public static void main(String[] args) throws Exception {
        String pdfUrl = "https://example.com/sample.pdf";
        String imagePath = "/path/to/output/image";
        PDFtoImageConverter.convertUsingPDFBox(pdfUrl, imagePath);
        PDFtoImageConverter.convertUsingIText(pdfUrl, imagePath);
    }
}

其中，PDFtoImageConverter.convertUsingPDFBox()方法使用pdfbox包转换pdf为图片，PDFtoImageConverter.convertUsingIText()方法使用itext包转换pdf为图片。可以根据需要选择其中的一个方法进行转换。同时，需要将pdfUrl替换为实际的pdf文件url，将imagePath替换为输出图片的路径和文件名前缀。