code: public static PrivateKey generatePrivateKey(String algorithm, KeySpec keySpec) {
  		return KeyUtil.generatePrivateKey(algorithm, keySpec);
  	}
docs: 生成私钥，仅用于非对称加密<br>
  算法见：https://docs.oracle.com/javase/7/docs/technotes/guides/security/StandardNames.html#KeyFactory
  
  @param algorithm 算法
  @param keySpec {@link KeySpec}
  @return 私钥 {@link PrivateKey}
  @since 3.1.1