code: public PrivateKey getPrivateKey_PKCS8Encoded(byte[] keyBytes){  
          try {
              PKCS8EncodedKeySpec spec = new PKCS8EncodedKeySpec(keyBytes);  
              KeyFactory keyFactory = KeyFactory.getInstance(algorithm);  
              return keyFactory.generatePrivate(spec); 
  		} catch (Exception e) {
  			log.error(e.getMessage(),e);
  		} 
      	return null;
      }
docs: 根据私钥字符串获取私钥
  Only RSAPrivate(Crt)KeySpec and PKCS8EncodedKeySpec supported for RSA private keys
  @param privateKey
  @return