code: private static PrivateKey commonGetPrivatekeyByText(String keyText)
              throws NoSuchAlgorithmException, InvalidKeySpecException {
          byte[] keyBytes = Base64.base64ToByteArray(keyText);
          PKCS8EncodedKeySpec pkcs8EncodedKeySpec = new PKCS8EncodedKeySpec(keyBytes);
          KeyFactory keyFactory = KeyFactory.getInstance(RSA);
          return keyFactory.generatePrivate(pkcs8EncodedKeySpec);
      }
docs: (common)通过私钥文本获取私钥