基于Apache PDFBox的PDF数字签名

在Java语言环境中完成数字签名主要基于itext-pdf、PDFBox两种工具，itext-pdf受商业限制，应用于商业服务中需要购买授权。PDFBox是apache基金会开源项目，基于apache2.0开源协议，不受商业限制，开发者可放心使用。以下是基于PDFBox的数字签名源码，使用该源码可使用PDFBox对PDF格式的文件进行数字。此外，完成数字签名还生成数字证书，全流程的数字签名示例可下载开源项目模拟数字签名全流程。开源数字签名访问地址：https://gitee.com/kaifangqian

`package org.resrun.sdk.pdfbox;

import org.resrun.sdk.pdfbox.vo.AssinaturaModel;

import org.apache.pdfbox.Loader;

import org.apache.pdfbox.cos.COSName;

import org.apache.pdfbox.io.IOUtils;

import org.apache.pdfbox.pdmodel.PDDocument;

import org.apache.pdfbox.pdmodel.PDPage;

import org.apache.pdfbox.pdmodel.PDPageContentStream;

import org.apache.pdfbox.pdmodel.PDResources;

import org.apache.pdfbox.pdmodel.common.PDRectangle;

import org.apache.pdfbox.pdmodel.common.PDStream;

import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;

import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;

import org.apache.pdfbox.pdmodel.interactive.annotation.PDAnnotationWidget;

import org.apache.pdfbox.pdmodel.interactive.annotation.PDAppearanceDictionary;

import org.apache.pdfbox.pdmodel.interactive.annotation.PDAppearanceStream;

import org.apache.pdfbox.pdmodel.interactive.digitalsignature.PDSignature;

import org.apache.pdfbox.pdmodel.interactive.digitalsignature.SignatureOptions;

import org.apache.pdfbox.pdmodel.interactive.form.PDAcroForm;

import org.apache.pdfbox.pdmodel.interactive.form.PDField;

import org.apache.pdfbox.pdmodel.interactive.form.PDSignatureField;

import org.apache.pdfbox.util.Matrix;

import java.awt.geom.AffineTransform;

import java.awt.geom.Rectangle2D;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.IOException;

import java.io.InputStream;

import java.security.KeyStoreException;

import java.security.NoSuchAlgorithmException;

import java.security.UnrecoverableKeyException;

import java.security.cert.CertificateException;

import java.util.Calendar;

import java.util.List;

public class AssinaturaPDF extends SignatureBase {

private SignatureOptions signatureOptions;

private AssinaturaModel assinatura;
public AssinaturaPDF(AssinaturaModel assinaturaModel) throws KeyStoreException, UnrecoverableKeyException, NoSuchAlgorithmException, IOException, CertificateException {
    super(assinaturaModel.getCertInfo());
    this.assinatura = assinaturaModel;
    if (assinaturaModel.getTsa() != null && !assinaturaModel.getTsa().equals("")) {
        setTsaUrl(assinaturaModel.getTsa());
    }
}

public byte [] assina() throws Exception {

    if (assinatura.getPdf() == null || assinatura.getPdf().length == 0) {
        throw new Exception("pdf file null");
    }

    try (ByteArrayOutputStream bos = new ByteArrayOutputStream();
         PDDocument doc = Loader.loadPDF(assinatura.getPdf())) {
        if (doc.isEncrypted()) {
            try {
                doc.setAllSecurityToBeRemoved(true);
            } catch (Exception e) {
                throw new Exception("pdf passwd error", e);
            }
        }

        int accessPermissions = SigUtils.getMDPPermission(doc);
        if (accessPermissions == 1)
        {
            throw new IllegalStateException("No changes to the document are permitted due to DocMDP transform parameters dictionary");
        }

        PDSignature signature = null;
        PDAcroForm acroForm = doc.getDocumentCatalog().getAcroForm(null);
        PDRectangle rect = null;

        // TODO  签名域的位置  可能需要再计算
        Rectangle2D humanRect = new Rectangle2D.Float(assinatura.getPosition().getParseX(), assinatura.getPosition().getParseY(),
                assinatura.getPosition().getSignWidthFloat(), assinatura.getPosition().getSignHeightFloat());

        // sign a PDF with an existing empty signature, as created by the CreateEmptySignatureForm example.
        if (acroForm != null)
        {
            signature = findExistingSignature(acroForm, assinatura.getSignatureKey());
            if (signature != null)
            {
                rect = acroForm.getField(assinatura.getSignatureKey()).getWidgets().get(0).getRectangle();
            }
        }

        if (signature == null)
        {
            // create signature dictionary
            signature = new PDSignature();
        }

        if (rect == null)
        {
            rect = createSignatureRectangle(doc, humanRect);
        }

        if (doc.getVersion() >= 1.5f && accessPermissions == 0)
        {
            SigUtils.setMDPPermission(doc, signature, 2);
        }

        if (acroForm != null && acroForm.getNeedAppearances())
        {
            // PDFBOX-3738 NeedAppearances true results in visible signature becoming invisible
            // with Adobe Reader
            if (acroForm.getFields().isEmpty())
            {
                // we can safely delete it if there are no fields
                acroForm.getCOSObject().removeItem(COSName.NEED_APPEARANCES);
                // note that if you've set MDP permissions, the removal of this item
                // may result in Adobe Reader claiming that the document has been changed.
                // and/or that field content won't be displayed properly.
                // ==> decide what you prefer and adjust your code accordingly.
            }
            else
            {
                System.out.println("/NeedAppearances is set, signature may be ignored by Adobe Reader");
            }
        }

        // default filter
        signature.setFilter(PDSignature.FILTER_ADOBE_PPKLITE);

        // subfilter for basic and PAdES Part 2 signatures
        signature.setSubFilter(PDSignature.SUBFILTER_ADBE_PKCS7_DETACHED);

        signature.setName("Name");
        signature.setLocation("Location");
        signature.setReason("Reason");

// the signing date, needed for valid signature

signature.setSignDate(Calendar.getInstance());

        signatureOptions = new SignatureOptions();
        signatureOptions.setVisualSignature(createVisualSignatureTemplate(doc, 0, rect, signature));
        signatureOptions.setPage(assinatura.getPosition().getPage());

// signatureOptions.setPreferredSignatureSize(SignatureOptions.DEFAULT_SIGNATURE_SIZE * 2);

        doc.addSignature(signature, this, signatureOptions);

// doc.saveIncremental(bos);

doc.saveIncremental(bos);

IOUtils.closeQuietly(signatureOptions);

doc.close();

return bos.toByteArray();

// return null;

}

}

private InputStream createVisualSignatureTemplate(PDDocument srcDoc, int pageNum,

PDRectangle rect, PDSignature signature) throws IOException

{

try (PDDocument doc = new PDDocument())

{

PDPage page = new PDPage(srcDoc.getPage(pageNum).getMediaBox());

doc.addPage(page);

PDAcroForm acroForm = new PDAcroForm(doc);

doc.getDocumentCatalog().setAcroForm(acroForm);

PDSignatureField signatureField = new PDSignatureField(acroForm);

PDAnnotationWidget widget = signatureField.getWidgets().get(0);

List acroFormFields = acroForm.getFields();

acroForm.setSignaturesExist(true);

acroForm.setAppendOnly(true);

acroForm.getCOSObject().setDirect(true);

acroFormFields.add(signatureField);

        widget.setRectangle(rect);

        // from PDVisualSigBuilder.createHolderForm()
        PDStream stream = new PDStream(doc);
        PDFormXObject form = new PDFormXObject(stream);
        PDResources res = new PDResources();
        form.setResources(res);
        form.setFormType(1);
        PDRectangle bbox = new PDRectangle(rect.getWidth(), rect.getHeight());
        float height = bbox.getHeight();
        Matrix initialScale = null;
        switch (srcDoc.getPage(pageNum).getRotation())
        {
            case 90:
                form.setMatrix(AffineTransform.getQuadrantRotateInstance(1));
                initialScale = Matrix.getScaleInstance(bbox.getWidth() / bbox.getHeight(), bbox.getHeight() / bbox.getWidth());
                height = bbox.getWidth();
                break;
            case 180:
                form.setMatrix(AffineTransform.getQuadrantRotateInstance(2));
                break;
            case 270:
                form.setMatrix(AffineTransform.getQuadrantRotateInstance(3));
                initialScale = Matrix.getScaleInstance(bbox.getWidth() / bbox.getHeight(), bbox.getHeight() / bbox.getWidth());
                height = bbox.getWidth();
                break;
            case 0:
            default:
                break;
        }
        form.setBBox(bbox);

        // from PDVisualSigBuilder.createAppearanceDictionary()
        PDAppearanceDictionary appearance = new PDAppearanceDictionary();
        appearance.getCOSObject().setDirect(true);
        PDAppearanceStream appearanceStream = new PDAppearanceStream(form.getCOSObject());
        appearance.setNormalAppearance(appearanceStream);
        widget.setAppearance(appearance);

        try (PDPageContentStream cs = new PDPageContentStream(doc, appearanceStream))
        {
            // for 90° and 270° scale ratio of width / height
            // not really sure about this
            // why does scale have no effect when done in the form matrix???
            if (initialScale != null)
            {
                cs.transform(initialScale);
            }

            // show background (just for debugging, to see the rect size + position)

// cs.setNonStrokingColor(Color.yellow);

// cs.addRect(-5000, -5000, 10000, 10000);

cs.fill();

            if (assinatura.getSignatureImage() != null)
            {

                PDImageXObject img =  PDImageXObject.createFromByteArray(doc,assinatura.getSignatureImage(),"test");
                int imgHeight = img.getHeight();
                int imgWidth = img.getWidth();
                cs.saveGraphicsState();
                cs.transform(Matrix.getScaleInstance(rect.getWidth()/imgWidth*1.0f,rect.getHeight()/imgHeight*1.0f));
                cs.drawImage(img, 0,0);
                cs.restoreGraphicsState();

            }
        }

        // no need to set annotations and /P entry

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        doc.save(baos);

// FileUtils.writeByteArrayToFile(new File("C:\Users\Administrator\Desktop\tem\pdfbox\sign-t.pdf"), baos.toByteArray());

return new ByteArrayInputStream(baos.toByteArray());

}

}

private PDRectangle createSignatureRectangle(PDDocument doc, Rectangle2D humanRect)
{
    float x = (float) humanRect.getX();
    float y = (float) humanRect.getY();
    float width = (float) humanRect.getWidth();
    float height = (float) humanRect.getHeight();
    PDPage page = doc.getPage(0);
    PDRectangle pageRect = page.getCropBox();
    PDRectangle rect = new PDRectangle();
    // signing should be at the same position regardless of page rotation.
    switch (page.getRotation())
    {
        case 90:
            rect.setLowerLeftY(x);
            rect.setUpperRightY(x + width);
            rect.setLowerLeftX(y);
            rect.setUpperRightX(y + height);
            break;
        case 180:
            rect.setUpperRightX(pageRect.getWidth() - x);
            rect.setLowerLeftX(pageRect.getWidth() - x - width);
            rect.setLowerLeftY(y);
            rect.setUpperRightY(y + height);
            break;
        case 270:
            rect.setLowerLeftY(pageRect.getHeight() - x - width);
            rect.setUpperRightY(pageRect.getHeight() - x);
            rect.setLowerLeftX(pageRect.getWidth() - y - height);
            rect.setUpperRightX(pageRect.getWidth() - y);
            break;
        case 0:
        default:
            rect.setLowerLeftX(x);
            rect.setUpperRightX(x + width);
            rect.setLowerLeftY(pageRect.getHeight() - y - height);
            rect.setUpperRightY(pageRect.getHeight() - y);
            break;
    }
    return rect;
}

private PDSignature findExistingSignature(PDAcroForm acroForm, String sigFieldName)
{
    PDSignature signature = null;
    PDSignatureField signatureField;
    if (acroForm != null)
    {
        signatureField = (PDSignatureField) acroForm.getField(sigFieldName);
        if (signatureField != null)
        {
            // retrieve signature dictionary
            signature = signatureField.getSignature();
            if (signature == null)
            {
                signature = new PDSignature();
                // after solving PDFBOX-3524
                // signatureField.setValue(signature)
                // until then:
                signatureField.getCOSObject().setItem(COSName.V, signature);
            }
            else
            {
                throw new IllegalStateException("The signature field " + sigFieldName + " is already signed.");
            }
        }
    }
    return signature;
}

}

`