code: public HMac init(String algorithm, SecretKey key){
  		try {
  			mac = Mac.getInstance(algorithm);
  			if(null != key){
  				this.secretKey = key;
  			}else{
  				this.secretKey = SecureUtil.generateKey(algorithm);
  			}
  			mac.init(this.secretKey);
  		} catch (Exception e) {
  			throw new CryptoException(e);
  		}
  		return this;
  	}
docs: 初始化
  @param algorithm 算法
  @param key 密钥 {@link SecretKey}
  @return {@link HMac}
  @throws CryptoException Cause by IOException