用java如何提取pdf中的标题和作者

Posted 2023-05-08

使用xpdf

PDDocument document=PDDocument.load(fis);
PDDocumentInformation info = document.getDocumentInformation();
System.out.println("页数:"+document.getNumberOfPages());

System.out.println( "标题:" + info.getTitle() );
System.out.println( "主题:" + info.getSubject() );
System.out.println( "作者:" + info.getAuthor() );
System.out.println( "关键字:" + info.getKeywords() );

System.out.println( "应用程序:" + info.getCreator() );
System.out.println( "pdf 制作程序:" + info.getProducer() );

System.out.println( "Trapped:" + info.getTrapped() );

System.out.println( "创建时间:" + dateFormat( info.getCreationDate() ));
System.out.println( "修改时间:" + dateFormat( info.getModificationDate())); 参考技术A pdf不是文本文件，是不能提取的。除非你把它转换成文本。 参考技术B 使用xunjiePDF编辑器 这个软件，进行提取。
1 在 PDF工具中打开 PDF 并选择“文档”>“提取页面”。
2 请指定要提取的页面的范围。
3 请在“提取页面”对话框中，执行以下一个或多个操作，然后单击 “确定”：

如何减小pdf中png图像的大小（压缩pdf中的png）

【中文标题】如何减小pdf中png图像的大小（压缩pdf中的png）

【英文标题】：how to reduce the size of png image in pdf (compress png in pdf)

【发布时间】：2020-08-18 18:13:38

【问题描述】：

我想通过将高分辨率图像替换为低分辨率图像来减小 pdf 文件的大小。要完成这个问题，我必须：

从 pdf 中提取图像（流） 压缩图片 用压缩图像替换 pdf 中的图像（流）

当我提取 png 图像并替换它们时，透明背景变为黑色背景。我从 pdf 中提取图像以找出原因。 pdf用于流式传输以保存png有一些非常奇怪的东西。因此，如果我尝试从 pdf 中提取 png 图像，我会得到两个不同的图像：一个 8 位彩色图像和一个 24 位彩色图像。

...
1 0 obj
<</Type/XObject/Subtype/Image/Width 1920/Height 1035/Length 24720/ColorSpace/DeviceGray/BitsPerComponent 8/Filter/FlateDecode>>stream
...
endstream
endobj
2 0 obj
<</Type/XObject/Subtype/Image/Width 1920/Height 1035/SMask 1 0 R/Length 47751/ColorSpace[/CalRGB<</Gamma[2.2 2.2 2.2]/Matrix[0.41239 0.21264 0.01933 0.35758 0.71517 0.11919 0.18045 0.07218 0.9504]/WhitePoint[0.95043 1 1.09]>>]/Intent/Perceptual/BitsPerComponent 8/Filter/FlateDecode>>stream
...
endstream
...

原图（透明背景的32位彩色图像）：

8 位彩色图像：

24 位彩色图像：

<dependency>
    <groupId>com.itextpdf</groupId>
    <artifactId>itextpdf</artifactId>
    <version>5.5.12</version>
</dependency>
<dependency>
    <groupId>org.apache.pdfbox</groupId>
    <artifactId>pdfbox</artifactId>
    <version>2.0.16</version>
</dependency>

ImageExtractor 将帮助您从 Pdf 文件中提取图像。

public class ImageExtractor 

    private static final Logger log = LoggerFactory.getLogger(ImageExtractor.class);

    public void extract(File pdf, File imageDir) throws IOException 
        if(!imageDir.exists()) 
            imageDir.mkdirs();
        
        PDDocument document = PDDocument.load(pdf);
        PDPageTree list = document.getPages();
        System.out.println("PDPageTree#count: " + list.getCount());
        int pageIndex = 1;
        for (PDPage page : list) 
            PDResources pdResources = page.getResources();
            System.out.println(pdResources.toString());
            for (COSName c : pdResources.getXObjectNames()) 
                System.out.println("PDResources[" + pageIndex + "]#COSName: " + c.getName());
                PDXObject o = pdResources.getXObject(c);
                System.out.println("PDResources[" + pageIndex + "]#PDXObject: " + o.toString());
                // https://github.com/mkl-public/testarea-itext5/blob/master/src/test/java/mkl/testarea/itext5/extract/ImageExtraction.java
                if (o instanceof PDImageXObject) 
                    PDImageXObject img = (PDImageXObject) o;
                    File file = new File(imageDir, pageIndex + "-" + System.nanoTime() + "." + img.getSuffix());
                    ImageIO.write(((PDImageXObject)o).getImage(), img.getSuffix(), file);
                
            
            pageIndex ++;
        
        log.info("Images have been extracted successfully! Check your images folder.");
    

ReplaceHightResolutionImage 是我用来减小 pdf 大小的代码。

package io.gitlab.donespeak.tutorial.pdf.reducesize.itext;

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.pdf.PRStream;
import com.itextpdf.text.pdf.PdfName;
import com.itextpdf.text.pdf.PdfNumber;
import com.itextpdf.text.pdf.PdfObject;
import com.itextpdf.text.pdf.PdfReader;
import com.itextpdf.text.pdf.PdfStamper;
import com.itextpdf.text.pdf.PdfStream;
import com.itextpdf.text.pdf.parser.PdfImageObject;
import io.gitlab.donespeak.tutorial.pdf.reducesize.imagecompress.ImageCompressor;
import io.gitlab.donespeak.tutorial.pdf.reducesize.imagecompress.SimpleCompress;

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class ReplaceHightResolutionImage 

    private ImageCompressor compressor;
    private double quality;
    private double scale;

    public ReplaceHightResolutionImage(double quality, double scale) 
        this.compressor = new SimpleCompress();
        this.quality = quality;
        this.scale = scale;
    

    public ReplaceHightResolutionImage(double quality, double scale, ImageCompressor compressor) 
        this.compressor = compressor;
        this.quality = quality;
        this.scale = scale;
    

    public void replace(File pdf, File output) throws IOException, DocumentException 
        PdfReader reader = new PdfReader(new FileInputStream(pdf));
        int n = reader.getXrefSize();
        PdfObject object;
        PRStream stream;

        for (int i = 0; i < n; i++) 

            object = reader.getPdfObject(i);
            stream = findImageStream(object);
            if (stream == null) 
                continue;
            
            PdfImageObject pdfImageObject = new PdfImageObject(stream);
            BufferedImage bi = pdfImageObject.getBufferedImage();
            if (bi == null) 
                continue;
            
            System.out.println("PdfReader#Xref: " + i + "," + pdfImageObject.getFileType());
            BufferedImage resultImage = compressor.compress(bi, pdfImageObject.getFileType(), quality, scale);
            replaceImage(stream, resultImage);
        

        PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(output));
        // furtherCompress(reader, stamper);
        stamper.close();
    

    private void furtherCompress(PdfReader reader, PdfStamper stamper) throws DocumentException 
        reader.removeFields();
        reader.removeUnusedObjects();
        stamper.setFullCompression();
        stamper.getWriter().setCompressionLevel(PdfStream.DEFAULT_COMPRESSION);
    

    private PRStream findImageStream(PdfObject object) 
        PRStream stream;
        if (object == null || !object.isStream()) 
            return null;
        
        stream = (PRStream)object;
        System.out.println(stream.getAsName(PdfName.SUBTYPE));
        if (!PdfName.IMAGE.equals(stream.getAsName(PdfName.SUBTYPE))) 
            // not jpg or png
            return null;
        
        PdfName pdfName = stream.getAsName(PdfName.FILTER);
        if (!PdfName.DCTDECODE.equals(pdfName) && !PdfName.FLATEDECODE.equals(pdfName)) 
            return null;
        
        // if (PdfName.DCTDECODE.equals(filter)) 
        //     return PdfImageObject.ImageBytesType.JPG.getFileExtension();
        //  else if (PdfName.JPXDECODE.equals(filter)) 
        //     return PdfImageObject.ImageBytesType.JP2.getFileExtension();
        //  else if (PdfName.FLATEDECODE.equals(filter)) 
        //     return PdfImageObject.ImageBytesType.PNG.getFileExtension();
        //  else if (PdfName.LZWDECODE.equals(filter)) 
        //     return PdfImageObject.ImageBytesType.CCITT.getFileExtension();
        // 
        return stream;
    

    private void replaceImage(PRStream stream, BufferedImage resultImage) throws IOException 

        ByteArrayOutputStream imgBytes = new ByteArrayOutputStream();
        ImageIO.write(resultImage, "JPG", imgBytes);

        stream.clear();
        stream.setData(imgBytes.toByteArray(), false, PRStream.NO_COMPRESSION);
        stream.put(PdfName.TYPE, PdfName.XOBJECT);
        stream.put(PdfName.SUBTYPE, PdfName.IMAGE);
        stream.put(PdfName.FILTER, PdfName.DCTDECODE);
        stream.put(PdfName.WIDTH, new PdfNumber(resultImage.getWidth()));
        stream.put(PdfName.HEIGHT, new PdfNumber(resultImage.getHeight()));
        stream.put(PdfName.BITSPERCOMPONENT, new PdfNumber(8));
        stream.put(PdfName.COLORSPACE, PdfName.DEVICERGB);
    

package io.gitlab.donespeak.tutorial.pdf.reducesize.itext;

public class ThumbnailatorCompressor implements ImageCompressor 

    @Override
    public BufferedImage compress(BufferedImage image, String imageFormat, double quality, double scale) throws IOException 
        System.out.println("ThumbnailatorCompressor#type: " + image.getType());
        // int imageType = "png".equalsIgnoreCase(imageFormat)? BufferedImage.TYPE_INT_ARGB: image.getType();
        BufferedImage thumbnail = Thumbnails.of(image)
            .imageType(image.getType())
            .scale(scale)
            .outputQuality(quality)
            // .outputFormat(imageFormat)
            .useOriginalFormat()
            .asBufferedImage();

        return thumbnail;
    

horse.pdf horse.png

public class ReplaceHightResolutionImageTest 

    @Test
    public void reduceWithThumbnailatorCompressor() throws IOException, DocumentException 
        double quality = 1d;
        double scale = 0.6d;
        File pdf = new File("pdf/asset/horse.pdf");
        File output = new File("pdf/target/output", "replaced-" + quality + "-" + scale);
        ReplaceHightResolutionImage replacer = new ReplaceHightResolutionImage(quality, scale, new SimpleCompress());
        replacer.replace(pdf, output);
    

【问题讨论】：

ISO-32000-1（又名 PDF 规范）仅支持两种类型的图像 - JPEG 和“原始位”。因此，任何不是 JPEG 的源图像格式都被转换为“原始位”——这包括 BMP、TIFF、GIF 等。PNG 由 4 个颜色通道组成：红色、绿色、蓝色和 Alpha。 RGB 本质上与位图图像相同； Alpha 是透明层。因此，iText 在 PDF 中模拟 PNG 的方法是在彼此之上添加不是一个而是两个图像：一个带有颜色的图像流和另一个带有透明蒙版的图像流。这是你提取的两张图片。

所以在我的ReplaceHightResolutionImage 中调用stream.clear() 会破坏png 流的结构并导致黑色背景。如果我想在pdf中压缩一个png图片，我该怎么办？

@DoneSpeak PDF 中没有 PNG 图像。有 JPEG 或原始位。没有PNG！您应该做的是将 RGB 和 Alpha（8 位）图像压缩为两个单独的 JPEG，并将它们替换为原始的、未压缩的原始位图像。

@datenwolf 感谢您的回答。正如您在我的描述中看到的那样，我尝试压缩每个流并将它们替换为原始流。但在那之后，具有透明背景的图像的背景变成了黑色。这让我很困扰。

“我认为应该有一种方法可以提取整个 png 图像并替换整个 png 图像，而不是单独处理 png 流的两个部分” - 有时一个如果可能的话，希望图像提取也将透明度添加到提取的 png 中。但这对您的用例没有帮助，jpeg 不支持透明度（至少不普遍支持），因此这种 完全替换方法 也会降低透明度。

【参考方案1】：

这是一个可行但不够好的答案。它可以很好地压缩 jpg 和 png。唯一的缺点是，如果您在许多页面中重复使用图像，它会将每个图像引用作为单独的流并生成一个新流来代替图像引用，这可能会导致更大的文件大小。

1 0 obj
<</Type/XObject/Subtype/Image/Width 1002/Height 564/Filter/DCTDecode/ColorSpace/DeviceRGB/BitsPerComponent 8/Length 89149>>stream
...
endstream
endobj
2 0 obj
<</Length 106/Filter/FlateDecode>>stream
x�m�=� ��w�^@|���=� 7�/����8�6��&b0$��
��N!o��L�,?Ck'�����c�h�x0��/(5c*�Y�سEX�o�Uj3�B�ݔ"
endstream
endobj
4 0 obj
<</Type/Page/MediaBox[0 0 595 842]/Resources<</XObject<</img0 1 0 R>>>>/Contents 2 0 R/Parent 3 0 R>>
endobj
5 0 obj
<</Length 106/Filter/FlateDecode>>stream
x�m�=� ��w�^@|���=�image    7�/����8�6��&b0$��
��N!o��L�,?Ck'�����c�h�x0��/(5c*�Y�سEX�o�Uj3�B�ݔ"
endstream
endobj
6 0 obj
<</Type/Page/MediaBox[0 0 595 842]/Resources<</XObject<</img0 1 0 R>>>>/Contents 5 0 R/Parent 3 0 R>>
endobj

package io.gitlab.donespeak.tutorial.pdf.reducesize;

import io.gitlab.donespeak.tutorial.pdf.reducesize.imagecompress.ThumbnailatorCompressor;
import org.apache.pdfbox.cos.COSName;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDDocumentCatalog;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.PDResources;
import org.apache.pdfbox.pdmodel.graphics.PDXObject;
import org.apache.pdfbox.pdmodel.graphics.image.JPEGFactory;
import org.apache.pdfbox.pdmodel.graphics.image.LosslessFactory;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;

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

public class RemoveAllImageFromPdf 

    public static void extractImages(File input, File imageDir) throws IOException 
        if(imageDir.exists()) 
            imageDir.delete();
        
        imageDir.mkdirs();
        PDDocument document = PDDocument.load(input);
        int pageIndex = 1;
        PDDocumentCatalog catalog = document.getDocumentCatalog();
        for (PDPage page : catalog.getPages()) 
            PDResources pdResources = page.getResources();
            System.out.println(pdResources.toString());
            for (COSName c : pdResources.getXObjectNames()) 
                System.out.println("PDResources[" + pageIndex + "]#COSName: " + c.getName());
                PDXObject o = pdResources.getXObject(c);
                System.out.println("PDResources[" + pageIndex + "]#PDXObject: " + o.toString());
                // https://github.com/mkl-public/testarea-itext5/blob/master/src/test/java/mkl/testarea/itext5/extract/ImageExtraction.java
                if (o instanceof PDImageXObject) 
                    PDImageXObject img = (PDImageXObject) o;
                    System.out.println(img.getSuffix() + "-" + img.getBitsPerComponent() + "-" + img.getColorSpace());
                    File file = new File(imageDir, pageIndex + "-" + c.getName() + "-" + img.getColorSpace() + "-" + System.nanoTime() + "." + img.getSuffix());
                    ImageIO.write(((PDImageXObject)o).getImage(), img.getSuffix(), file);
                
            
            pageIndex ++;
        
        // document.save(output);
    

    /**
     *
     * @param input
     * @param output
     * @throws IOException
     */
    public static void compress(File input, File output) throws IOException 
        if(!output.getParentFile().exists()) 
            output.getParentFile().mkdirs();
        
        ThumbnailatorCompressor compressor = new ThumbnailatorCompressor();
        PDDocument document = PDDocument.load(input);
        int pageIndex = 1;
        PDDocumentCatalog catalog = document.getDocumentCatalog();

        for (PDPage page : catalog.getPages()) 
            PDResources pdResources = page.getResources();
            for (COSName c : pdResources.getXObjectNames()) 
                System.out.println("PDResources[" + pageIndex + "]#COSName: " + c.getName());
                PDXObject o = pdResources.getXObject(c);
                System.out.println("PDResources[" + pageIndex + "]#PDXObject: " + o.toString());
                // https://github.com/mkl-public/testarea-itext5/blob/master/src/test/java/mkl/testarea/itext5/extract/ImageExtraction.java
                if (o instanceof PDImageXObject) 
                    PDImageXObject img = (PDImageXObject) o;
                    BufferedImage bufferedImage = compressor.compress(img.getImage(), img.getSuffix(), 0.8, 0.5);
                    PDImageXObject imgNew = null;
                    System.out.println("img(w, h): (" + img.getWidth() + "," + img.getHeight() + ")");
                    System.out.println("bufferedImage(w, h): (" + bufferedImage.getWidth() + "," + bufferedImage.getHeight() + ")");
                    if("png".equalsIgnoreCase(img.getSuffix())) 
                        imgNew = LosslessFactory.createFromImage(document, bufferedImage);
                     else 
                        imgNew = JPEGFactory.createFromImage(document, bufferedImage);
                    
                    pdResources.put(c, imgNew);
                
            
            pageIndex ++;
        
        if(!output.getParentFile().exists()) 
            output.getParentFile().mkdirs();
        
        document.save(output);
        document.close();
    

通过以下方法直接处理文档中的对象，或许可以解决上面的问题。但我不知道如何以这种方式替换流。

new com.itextpdf.text.pdf.PdfReader(new FileInputStream(pdf)).getPdfObject(i);
// or
org.apache.pdfbox.pdmodel.PDDocument.load(pdf).getDocument().getObjects()