itext错误“线程“ main”中的异常java.lang.NullPointerException”

Question

您好，我对Java和使用itext还是很陌生。 这个想法是用pdf格式进行数字签名。 源代码是从这里开始的 ，并且对路径进行了一些调整。

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);
}
}

运行此后，我得到错误：

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

有解决的想法吗？ 非常感谢

Answer 1

这意味着您的path变量在signPdf方法中为null 。 您正在加载的属性文件没有名为PRIVATE属性。