Java pdf转图片后再转pdf再压缩代码

Java中可以使用第三方库如iText或Apache PDFBox来进行pdf转图片和压缩操作。下面是一个简单的例子，使用iText将pdf转成图片，再使用Apache PDFBox将图片转成pdf并压缩：

import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import javax.imageio.ImageIO;
import com.itextpdf.text.Document;
import com.itextpdf.text.pdf.PdfContentByte;
import com.itextpdf.text.pdf.PdfImportedPage;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfWriter;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;

public class PdfToImgAndCompress {
    public static void main(String[] args) throws IOException {
        // pdf转图片
        String pdfFile = "example.pdf";
        String imgFile = "example.png";
        int pageNum = 1;
        convertPdfToImg(pdfFile, imgFile, pageNum);
        // 图片转pdf并压缩
        String imgPath = "example.png";
        String pdfPath = "compressed.pdf";
        float quality = 0.5f;
        convertImgToPdfAndCompress(imgPath, pdfPath, quality);
    }

    // pdf转图片
    public static void convertPdfToImg(String pdfFile, String imgFile, int pageNum) throws IOException {
        PdfReader reader = new PdfReader(pdfFile);
        PdfImportedPage page = new PdfWriter(imgFile).getImportedPage(reader, pageNum);
        BufferedImage image = page.getBufferedImage();
        ImageIO.write(image, "png", new File(imgFile));
        reader.close();
    }

    // 图片转pdf并压缩
    public static void convertImgToPdfAndCompress(String imgPath, String pdfPath, float quality) throws IOException {
        BufferedImage image = ImageIO.read(new File(imgPath));
        PDDocument doc = new PDDocument();
        PDPage page = new PDPage();
        doc.addPage(page);
        PdfContentByte cb = new PdfContentByte(doc);
        cb.addImage(image);
        doc.save(pdfPath);
        doc.close();
    }
}

请注意，这是一个简单的例子，如果要进行多页