PDFBox 2.0.8-从一个文档中提取图像并在另一个文档中使用

Question

I am writing a Java application to work as a template reader and writer. I have had success with working with text, but having some dificulty with the images...

Getting the images was the easy part - using a class extending PDFStreamEngine

package readingPdf;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.pdfbox.contentstream.PDFStreamEngine;
import org.apache.pdfbox.contentstream.operator.DrawObject;
import org.apache.pdfbox.contentstream.operator.Operator;
import org.apache.pdfbox.contentstream.operator.state.Concatenate;
import org.apache.pdfbox.contentstream.operator.state.Restore;
import org.apache.pdfbox.contentstream.operator.state.Save;
import org.apache.pdfbox.contentstream.operator.state.SetGraphicsStateParameters;
import org.apache.pdfbox.contentstream.operator.state.SetMatrix;
import org.apache.pdfbox.cos.COSBase;
import org.apache.pdfbox.cos.COSName;
import org.apache.pdfbox.pdmodel.graphics.PDXObject;
import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.util.Matrix;

public class ImageStripper extends PDFStreamEngine {

    ArrayList<Object  []> imagesData = null;
    public ImageStripper() throws IOException {
        // preparing PDFStreamEngine
        addOperator(new Concatenate());
        addOperator(new DrawObject());
        addOperator(new SetGraphicsStateParameters());
        addOperator(new Save());
        addOperator(new Restore());
        addOperator(new SetMatrix());
        imagesData = new ArrayList<Object[]>();
    }

    @Override
    protected void processOperator(Operator operator, List<COSBase> operands) throws IOException {
        String operation = operator.getName();
        if ("Do".equals(operation)) {
            COSName objectName = (COSName) operands.get(0);
            // get the PDF object
            PDXObject xobject = getResources().getXObject(objectName);
            // check if the object is an image object
            if (xobject instanceof PDImageXObject) {
                Object[] imageData = new Object[3];
                PDImageXObject image = (PDImageXObject) xobject;

                Matrix ctmNew = getGraphicsState().getCurrentTransformationMatrix();

                // position of image in the pdf in terms of user space units
                System.out.println("position in PDF = " + ctmNew.getTranslateX() + ", " + ctmNew.getTranslateY()
                        + " in user space units");

                imageData[0] = ctmNew.getTranslateX();// xPos
                imageData[1] = ctmNew.getTranslateY();// yPos

                imageData[2] = image;//Image

                imagesData.add(imageData);

            } else if (xobject instanceof PDFormXObject) {
                PDFormXObject form = (PDFormXObject) xobject;
                showForm(form);
            }
        } else {
            super.processOperator(operator, operands);
        }
    }

    public ArrayList<Object[]> getImagesList(){
        return imagesData;
    }
}

next is the implementation thereof

public class PDFManager{

    private PDFParser parser;
    private PDDocument pdDoc;
    private PDDocument retDoc;
    private COSDocument cosDoc;
    private PDPage page;
    private String filePath;
    private File file; 

    public PDDocument transferImage() throws IOException {
        this.pdDoc = null;
        this.cosDoc = null;

        file = new File(filePath);
        parser = new PDFParser(new RandomAccessFile(file, "r"));
        parser.parse();
        cosDoc = parser.getDocument();
        pdDoc = new PDDocument(cosDoc);

        //Get Image Data
        ImageStripper imageStripper = new ImageStripper();
        imageStripper.processPage(pdDoc.getPage(0));
        ArrayList<Object []> imageList = imageStripper.getImagesList();

        //Close Doc
        pdDoc.close();
        cosDoc.close();

        //Create new PDF Doc
        retDoc = new PDDocument();
        page = new PDPage(new PDRectangle(PDRectangle.A4.getHeight(), PDRectangle.A4.getWidth())); 
        retDoc.addPage(page);

        PDPageContentStream cs = new PDPageContentStream(retDoc, page, AppendMode.OVERWRITE, true);

        for(int pos = 0; pos < imageList.size() ; pos++) {
            Object [] imageData = imageList.get(pos);

            float xPos = (float)imageData[0];
            float yPos = (float)imageData[1];
            PDImageXObject image = (PDImageXObject)imageData[2];
            cs.drawImage(image, xPos, yPos);
        }

        cs.close();
        return retDoc;
    }

    public static void main(String[] args) throws IOException {

        PDFManager pdfManager = new PDFManager();

        PDDocument doc =pdfManager.ToText("c:\\test\\test.pdf"); 

        doc.save("c:\\test\\test2.pdf");
        doc.close();
    }
}

Now the problem comes in at the point where I am writing calling the cs.drawImage . All the code executes without any issue except when trying to save the new file... I get the exception COSStream has been closed and cannot be read. Perhaps its enclosing PDDocument has been closed? COSStream has been closed and cannot be read. Perhaps its enclosing PDDocument has been closed?

I suspect that there is still metadata linking the image to the original Document it was extracted from as calling PDImageXobject.createFromFile("c:\\\\test\\\\testImage.png", doc) returns a new instance of PDImageXObject which writes perfectly. As the PDDocument that gets written to gets passed into the PDImageXObject I suspect it gets linked in some way or another.

I can not save the image to a temp location as this is just testing for a POC.

Any assistance would be appreciated

Answer 1

@ Tilman Hausherr

Thanks for the solution

I moved the closing of the original document into a seperate method which I called after writing the file

public void closeFiles(){
    pdDoc.close();
    cosDoc.close();
}