Question

Hello there I’m quite new to java and working with itext. The idea is to make digital signature in pdf. Source code is from here with some adjustments with paths..

package signaturefield;

public class Signaturefield {

 /** The resulting PDF */
public static String ORIGINAL = "c:/Users/example.pdf";
/** The resulting PDF */
public static String SIGNED1 = "c:/Users/signed_1.pdf";
/** The resulting PDF */
public static String SIGNED2 = "c:/Users/signed_2.pdf";

/** One of the resources. */
public static final String RESOURCE
    = "C:/Users/watermark.png";

/**
 * A properties file that is PRIVATE.
 * You should make your own properties file and adapt this line.
 */
public static String PATH = "c:/Users/key.properties";
/** Some properties used when signing. */
public static Properties properties = new Properties();
private PrivateKey pk;

/**
 * Creates a PDF document.
 * @param filename the path to the new PDF document
 * @throws DocumentException 
 * @throws IOException 
 */
public void createPdf(String filename) throws IOException, DocumentException {
    // step 1
    Document document = new Document();
    // step 2
    PdfWriter writer = PdfWriter.getInstance(document, new FileOutputStream(filename));
    // step 3
    document.open();
    // step 4
    document.add(new Paragraph("Hello World!"));
    PdfFormField field = PdfFormField.createSignature(writer);
    field.setWidget(new Rectangle(72, 732, 144, 780), PdfAnnotation.HIGHLIGHT_INVERT);
    field.setFieldName("mySig");
    field.setFlags(PdfAnnotation.FLAGS_PRINT);
    field.setPage();
    field.setMKBorderColor(BaseColor.BLACK);
    field.setMKBackgroundColor(BaseColor.WHITE);
    PdfAppearance tp = PdfAppearance.createAppearance(writer, 72, 48);
    tp.rectangle(0.5f, 0.5f, 71.5f, 47.5f);
    tp.stroke();
    field.setAppearance(PdfAnnotation.APPEARANCE_NORMAL, tp);
    writer.addAnnotation(field);
    // step 5
    document.close();
}

/**
 * Manipulates a PDF file src with the file dest as result
 * @param src the original PDF
 * @param dest the resulting PDF
 * @throws GeneralSecurityException 
 * @throws IOException 
 * @throws DocumentException 
 * @throws FileNotFoundException 
 * @throws KeyStoreException 
 * @throws Exception 
 */
public void signPdf(String src, String dest, boolean certified, boolean graphic) throws GeneralSecurityException, IOException, DocumentException {
    // private key and certificate
    String path = properties.getProperty("PRIVATE");
    String keystore_password = properties.getProperty("PASSWORD");
    String key_password = properties.getProperty("PASSWORD");
    KeyStore ks = KeyStore.getInstance("pkcs12", "BC");
    ks.load(new FileInputStream(path), keystore_password.toCharArray());
    String alias = (String)ks.aliases().nextElement();
    PrivateKey pk = (PrivateKey)ks.getKey(alias, key_password.toCharArray());
    Certificate[] chain = ks.getCertificateChain(alias);
    // reader and stamper
    PdfReader reader = new PdfReader(ORIGINAL);
    PdfStamper stamper = PdfStamper.createSignature(reader, new FileOutputStream(dest), '\0');
    // appearance
    PdfSignatureAppearance appearance = stamper.getSignatureAppearance();
    appearance.setVisibleSignature("mySig");
    appearance.setReason("It's personal.");
    appearance.setLocation("Foobar");
    if (certified) {
        appearance.setCertificationLevel(PdfSignatureAppearance.CERTIFIED_NO_CHANGES_ALLOWED);
    }
    if (graphic) {
        appearance.setSignatureGraphic(Image.getInstance(RESOURCE));
        appearance.setRenderingMode(PdfSignatureAppearance.RenderingMode.GRAPHIC);
    }
    // signature
    ExternalSignature es = new PrivateKeySignature(pk, "SHA-256", "BC");
    ExternalDigest digest = new BouncyCastleDigest();
    MakeSignature.signDetached(appearance, digest, es, chain, null,null, null, 0, CryptoStandard.CMS);
}


public static void main(String[] args)
    throws Exception {
    Security.addProvider(new BouncyCastleProvider());
    properties.load(new FileInputStream(PATH));
    Signaturefield signatures = new Signaturefield();
    signatures.createPdf(ORIGINAL);
    signatures.signPdf(ORIGINAL, SIGNED1, false, false);
    signatures.signPdf(ORIGINAL, SIGNED2, true, true);
}
}

after running this i get error:

Exception in thread "main" java.lang.NullPointerException
    at java.io.FileInputStream.<init>(FileInputStream.java:134)
    at java.io.FileInputStream.<init>(FileInputStream.java:97)
    at signaturefield.Signaturefield.signPdf(Signaturefield.java:114)
    at signaturefield.Signaturefield.main(Signaturefield.java:146)
Java Result: 1

Any idea of fixing it? thanks alot

Answer 1

That means that you path variable is null in signPdf method. Properties file which you are loading don’t have property named PRIVATE.