Java Applet中的PdfStamper

我在Java applet中使用PdfStamper来签署pdf文件 . 问题是每次使用pdfStamper.close（）时到达行时，applet都会挂起;我认为我的问题与一些java applet策略有关但我已经授予所有权限：

grant {
  permission java.security.AllPermission;
};

我的代码是：

import com.lowagie.text.DocumentException;
import com.lowagie.text.Rectangle;
import com.lowagie.text.pdf.PdfReader;
import com.lowagie.text.pdf.PdfSignatureAppearance;
import com.lowagie.text.pdf.PdfStamper;
import java.io.BufferedReader;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.security.AccessController;
import java.security.KeyStore;
import java.security.KeyStoreException;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PrivilegedAction;
import java.security.UnrecoverableKeyException;
import java.security.cert.Certificate;
import java.security.cert.CertificateException;
import java.util.Enumeration;
import javax.swing.JApplet;

public class SignApplet extends JApplet {

    public void test() {
        AccessController.doPrivileged( new PrivilegedAction() {
            @Override
            public Object run() {
                try {
                    KeyStore keyStore = KeyStore.getInstance( "PKCS11-custom_name" );

                    String pin = "custom_pin";
                    keyStore.load( null, pin.toCharArray() );
                    Enumeration<String> aliases = keyStore.aliases();

                    String alias = aliases.nextElement();
                    PrivateKey key = ( PrivateKey ) keyStore.getKey( alias, pin.toCharArray() );
                    Certificate[] chain = keyStore.getCertificateChain( alias );

                    String unsigned_pdf = "C:\\Users\\user_name\\unsigned.pdf";
                    String signed_pdf = "C:\\Users\\user_name\\signed.pdf";

                    PdfReader pdfReader = new PdfReader( (new File( unsigned_pdf )).getAbsolutePath() );
                    File outputFile = new File( signed_pdf );
                    PdfStamper pdfStamper;
                    pdfStamper = PdfStamper.createSignature( pdfReader, null, '\0', outputFile );
                    PdfSignatureAppearance sap = pdfStamper.getSignatureAppearance();
                    sap.setCrypto( key, chain, null, PdfSignatureAppearance.SELF_SIGNED );
                    sap.setReason( "reason" );
                    sap.setLocation( "" );
                    sap.setVisibleSignature( new Rectangle( 10, 10, 50, 30 ), 1, null );

                    pdfStamper.setFormFlattening( true );
                    pdfStamper.close(); // -- applet suspends right there

                } catch ( Exception ex ) {
                    ex.printStackTrace();
                }
                return null;
            }
        } );
    }
}

我从那样的html运行它：

<APPLET CODE="SignApplet.class" NAME="SIGNAPPLET" ARCHIVE="SignApplet-1.0.jar, itext-2.1.7.jar" WIDTH="0" HEIGHT="0"></APPLET> 
<h:form>
    <h:button onclick="document.SIGNAPPLET.test();" value="--- TEST ---" />
</h:form>

密钥库来自USB令牌 .

在java调试控制台中，我没有看到任何异常 . 当我从main方法运行相同的源代码时（对传递参数几乎没有修改），它运行得很好 .

不知道是什么问题？