public static String getTokenTwo (String appId, String packag) throws IOException, SignatureException, NoSuchAlgorithmException, InvalidKeyException {

        String nonceStr = getRandomString(32);
        long timestamp = System.currentTimeMillis() / 1000;
        String message = buildMessageTwo( appId,timestamp,nonceStr,packag);
        String signature = sign(message.getBytes("utf-8"));

        return signature;
    }
private static String buildMessageTwo(String appId, long timestamp, String nonceStr, String packag) {
    return appId + "\n"
            + timestamp + "\n"
            + nonceStr + "\n"
            + packag + "\n";
}
private static String sign(byte[] message) throws NoSuchAlgorithmException, SignatureException, IOException, InvalidKeyException {
    Signature sign = Signature.getInstance("SHA256withRSA"); //SHA256withRSA

    PrivateKey privateKey = getPrivateKey("密钥文件地址");
    sign.initSign(privateKey);
    sign.update(message);
    return Base64.getEncoder().encodeToString(sign.sign());
}