code: public static PrivateKey loadPrivateKey(String privateKeyStr) throws Exception {
  		try {
  			byte[] buffer = base64.decode(privateKeyStr);
  			// X509EncodedKeySpec keySpec = new X509EncodedKeySpec(buffer);
  			PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(buffer);
  			KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);
  			return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
  		} catch (NoSuchAlgorithmException e) {
  			throw new Exception("无此算法");
  		} catch (InvalidKeySpecException e) {
  			throw new Exception("私钥非法");
  		} catch (NullPointerException e) {
  			throw new Exception("私钥数据为空");
  		}
  	}
docs: 从字符串中加载私钥<br>
  加载时使用的是PKCS8EncodedKeySpec（PKCS#8编码的Key指令）。
  
  @param privateKeyStr
  @return
  @throws Exception