Generating a .pfx with java applet

Question

I'm trying to do an applet that generate a .pfx file from a X509Certificate but i have some doubts.
This is correct?
                KeyStore keyS = KeyStore.getInstance("PKCS12", "BC");
                keyS.load(null,null);
                keyS.setCertificateEntry(certFirmado.getSerialNumber().toString(), certFirmado);
                keyS.setKeyEntry(certFirmado.getSerialNumber().toString(), privada, pass, new X509Certificate[]{certFirmado});////this is what i´m not sure
                FileOutputStream out = new FileOutputStream(savePath+".pfx");
                keyS.store(out, pass);
                out.close();when i'm generating the keystore, in chain i have to put the certificate?
Is this correct to generate a .pfx?
thanks
My code:
private boolean guardarCertificado(PrivateKey privada, X509Certificate certFirmado,char[] pass) throws KeyStoreException, NoSuchProviderException, IOException, NoSuchAlgorithmException, CertificateException {
        JFileChooser chooser = new JFileChooser();
        chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
        int status = chooser.showSaveDialog(jPanel1);
        if(status == JFileChooser.APPROVE_OPTION){
            File saveFile = chooser.getSelectedFile();
            String savePath = saveFile.getAbsolutePath();
            if (!(new File(savePath+".pfx").exists())){
                KeyStore keyS = KeyStore.getInstance("PKCS12", "BC");
                keyS.load(null,null);
                keyS.setCertificateEntry(certFirmado.getSerialNumber().toString(), certFirmado);
                keyS.setKeyEntry(certFirmado.getSerialNumber().toString(), privada, pass, new X509Certificate[]{certFirmado});
                FileOutputStream out = new FileOutputStream(savePath+".pfx");
                keyS.store(out, pass);
                out.close();
                return true;
            }else{
                int answer = JOptionPane.showConfirmDialog(jPanel1, "Ya existe un archivo con ese nombre. ¿Desea reemplazarlo?","Descarga",JOptionPane.YES_NO_OPTION);
                if (answer == JOptionPane.YES_OPTION) {
                    KeyStore keyS = KeyStore.getInstance("PKCS12", "BC");
                    keyS.load(null,null);
                    keyS.setCertificateEntry(certFirmado.getSerialNumber().toString(), certFirmado);
                    keyS.setKeyEntry(certFirmado.getSerialNumber().toString(), privada, pass, new Certificate[]{certFirmado});
                    FileOutputStream out = new FileOutputStream(savePath+".pfx");
                    keyS.store(out, pass);
                    out.close();
                    return true;
                } else if (answer == JOptionPane.NO_OPTION) {
                  return false;
        return false;
    }

Answer 1

Thanks for your help. You're saying I just need to use setKeyEntry?
Then the code would stay this way:
private boolean guardarCertificado(PrivateKey privada, X509Certificate certFirmado, X509Certificate certCA,char[] pass) throws KeyStoreException, NoSuchProviderException, IOException, NoSuchAlgorithmException, CertificateException {
        JFileChooser chooser = new JFileChooser();
        chooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
        int status = chooser.showSaveDialog(jPanel1);
        if(status == JFileChooser.APPROVE_OPTION){
            File saveFile = chooser.getSelectedFile();
            String savePath = saveFile.getAbsolutePath();
            if (!(new File(savePath+".pfx").exists())){
                KeyStore keyS = KeyStore.getInstance("PKCS12", "BC");
                keyS.load(null,null);
                //keyS.setCertificateEntry(certFirmado.getSerialNumber().toString(), certFirmado);
                keyS.setKeyEntry(certFirmado.getSerialNumber().toString(), privada, pass, new X509Certificate[]{certFirmado,certCA});
                FileOutputStream out = new FileOutputStream(savePath+".pfx");
                keyS.store(out, pass);
                out.close();
                return true;
            }else{
                int answer = JOptionPane.showConfirmDialog(jPanel1, "Ya existe un archivo con ese nombre. ¿Desea reemplazarlo?","Descarga",JOptionPane.YES_NO_OPTION);
                if (answer == JOptionPane.YES_OPTION) {
                    KeyStore keyS = KeyStore.getInstance("PKCS12", "BC");
                    keyS.load(null,null);
                    //keyS.setCertificateEntry(certFirmado.getSerialNumber().toString(), certFirmado);
                    keyS.setKeyEntry(certFirmado.getSerialNumber().toString(), privada, pass, new Certificate[]{certFirmado,certCA});
                    FileOutputStream out = new FileOutputStream(savePath+".pfx");
                    keyS.store(out, pass);
                    out.close();
                    return true;
                } else if (answer == JOptionPane.NO_OPTION) {
                  return false;
        return false;
    }With respect to generating the request. What extensions do you recommend? The certificate will be used to sign documents.