Java 调用 pkcs#11的dll库，获取到的KeyStore 的size为0，是什么原因？

Question

插入USB-KEY， 想通过HttpClient来向服务器发送https请求。现在厂商已提供的USB-KEY的驱动程序PKCS#11接口，于是通过java程序访问USB-KEY。

代码如下

// 厂商提供的UKEY型号名称
private static final String UKEY_PROVIDER = "SJK1217";

// UKEY驱动lib库文件
private static final String UKEY_LIB = "E:/cer/System32/SJK1217Pkcs.dll";

// UKEY的PIN码
private static final String UKEY_PIN = "1234";

private static String keystorePath = "E:/cer/hxx_sign.keystore";

private static String keystorePass = "12345678";

public static void main(String[] args) throws Exception {
        String pkcs11config = "name = " + UKEY_PROVIDER + "\nlibrary = "+ UKEY_LIB + "\n";
        byte[] pkcs11configbytes = pkcs11config.getBytes();
        ByteArrayInputStream configStream = new ByteArrayInputStream(pkcs11configbytes);
        SunPKCS11 ps = new sun.security.pkcs11.SunPKCS11(configStream);
        System.out.println(ps.toString());

        Security.addProvider(ps);

        KeyStore.CallbackHandlerProtection pinHandler = new KeyStore.CallbackHandlerProtection(new TextCallbackHandler());

        KeyStore ks = KeyStore.Builder.newInstance("PKCS11", ps, pinHandler)
                .getKeyStore();

        ks.load(null, UKEY_PIN.toCharArray());

        printKeyStoreInfo(ks);
    }
    
    // 打印 KeyStore中的信息
public static void printKeyStoreInfo(KeyStore keystore) throws Exception {
    System.out.println("Provider : " + keystore.getProvider().getName());
    System.out.println("Type : " + keystore.getType());
    System.out.println("Size : " + keystore.size());

    Enumeration en = keystore.aliases();
    while (en.hasMoreElements()) {
        String alias = (String) en.nextElement();
        System.out.println("Alias: " + alias);

        X509Certificate cert = (X509Certificate) keystore
                .getCertificate(alias);
        System.out.println("Certificate: " + cert);

        PrivateKey privateKey = (PrivateKey) keystore.getKey(alias, null);
        System.out.println("Private key: " + privateKey);
    }
}

---

打印的结果

SunPKCS11-SJK1217 version 1.8
Provider : SunPKCS11-SJK1217
Type : PKCS11
Size : 0

获取到的KeyStore 的size为0，是什么原因？ 国内这方面的资料好难搜索得到，有这方面的大牛 能帮忙解答一下么？