code: public static byte[] generateHmacSha1Key() {
  		try {
  			KeyGenerator keyGenerator = KeyGenerator.getInstance(HMACSHA1_ALG);
  			keyGenerator.init(DEFAULT_HMACSHA1_KEYSIZE);
  			SecretKey secretKey = keyGenerator.generateKey();
  			return secretKey.getEncoded();
  		} catch (GeneralSecurityException e) {
  			throw ExceptionUtil.unchecked(e);
  		}
  	}
docs: 生成HMAC-SHA1密钥,返回字节数组,长度为160位(20字节). HMAC-SHA1算法对密钥无特殊要求, RFC2401建议最少长度为160位(20字节).