PDF签名itext pkcs7多重标志

我想在pdf文档上做多个签名，就像在工作流程中一样 . 我正在使用以下代码签署我写的pdf，工作正常 .

得到哈希

public String getHash() {
    LOGGER.debug("PDFSigner.getHash : method invoked");
    String pdfHashValue = null;
    try {
        int contentEstimated = PDFSigner.CONTENT_ESTIMATED;//8192
        HashMap<PdfName, Integer> exc = new HashMap<>();
        exc.put(PdfName.CONTENTS, contentEstimated * 2 + 2);
        PdfSignature pdfSignature = new PdfSignature(PdfName.ADOBE_PPKLITE,
                PdfName.ADBE_PKCS7_DETACHED);
        pdfSignature.setReason(appearance.getReason());
        pdfSignature.setLocation(appearance.getLocation());
        pdfSignature.setContact(appearance.getContact());
        pdfSignature.setDate(new PdfDate(appearance.getSignDate()));
        appearance.setCryptoDictionary(pdfSignature);
        appearance.preClose(exc);
        InputStream data = appearance.getRangeStream();
        MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
        byte buf[] = new byte[contentEstimated];
        int n = 0;
        while ((n = data.read(buf, 0, contentEstimated)) > 0) {
            messageDigest.update(buf, 0, n);
        }
        byte hash[] = messageDigest.digest();
        byte[] reqBytesdata = Hex.encode(hash);
        pdfHashValue = new String(reqBytesdata, "UTF8"); 
    } catch (Exception exp) {
        LOGGER.error("PDFSigner error occured getHash", exp);
    }
    return pdfHashValue;
}

签署文件

//dSignature is the received encoded signature pkcs7 (SHA256).
//starts with MIIOWQYJKoZIhvcNAQcCo.....
    public boolean doSign(String dSignature) throws IOException, DocumentException {

        boolean pdfGenerationStatus = false;
        try {
            byte[] PKCS7Response = Base64.decode(dSignature
                    .getBytes("UTF8"));
            byte[] paddedSig = new byte[PDFSigner.CONTENT_ESTIMATED];
            System.arraycopy(PKCS7Response, 0, paddedSig, 0,
                    PKCS7Response.length);
            PdfDictionary pdfDictionary = new PdfDictionary();
            pdfDictionary.put(PdfName.CONTENTS,
                    new PdfString(paddedSig).setHexWriting(true));  
            appearance.close(pdfDictionary);
            pdfGenerationStatus = true;

        } catch (Exception exp) {
            LOGGER.error("doSign ", exp);
        }
        return pdfGenerationStatus; 

    }

以上代码工作正常 . 我的新要求是添加多个签名 . 有没有办法重复使用此代码段 . 我经历了this，this和this但没有运气 .

除了我尝试的是，创建空白多个空白签名并尝试附加签名 . 但它导致创建损坏的文件 . 我也尝试使用link中提到的方法创建文件 . MakeSignature.signExternalContainer 还通过了一个伟大的文档PDF文档的数字签名

用例就像

• 创建pdf

• 生成doc hash

• 发送到外部服务器

• 外部服务器将返回pkcs7 base64编码的字符串

• 将签名附加到pdf

UPDATE

代码更改是针对'追加模式'，代码更改后我的代码支持多重签名，感谢@Paulo Soares，@ mlk

private void initAppearanceAppend(String customerName) throws IOException, DocumentException {
    System.out.println("PDFSigner.initAppearanceAppend");
    PdfReader readerpdf = new PdfReader(this.getInputPdfFilePath());
    int lastPageNumber = readerpdf.getNumberOfPages();
    this.pdfSignatureMetaData.setPageNumber(lastPageNumber);
    this.pdfSignatureMetaData.setSignerName(customerName);
    //this.pdfSignatureMetaData.setPageNumber(PDFSigner.SIGNATURE_PAGE_NUMBER);
    OutputStream fout = new FileOutputStream(this.outputPdfFilePath);
    //PdfStamper stamperpdf = PdfStamper.createSignature(readerpdf, fout, '\0'); OLD CODE WITHOUT APPEND MODE
    PdfStamper stamperpdf = PdfStamper.createSignature(readerpdf, fout, '\0', new File("E://temp"), true);

    this.appearance = stamperpdf.getSignatureAppearance();
    LOGGER.debug("PDFSigner.initAppearanceAppend : default configurations are made");
}