code: public static final Mac getInstance(String algorithm, String provider)
              throws NoSuchAlgorithmException, NoSuchProviderException {
          Instance instance = JceSecurity.getInstance
                  ("Mac", MacSpi.class, algorithm, provider);
          return new Mac((MacSpi)instance.impl, instance.provider, algorithm);
      }
docs: Returns a <code>Mac</code> object that implements the
  specified MAC algorithm.
  
  <p> A new Mac object encapsulating the
  MacSpi implementation from the specified provider
  is returned.  The specified provider must be registered
  in the security provider list.
  
  <p> Note that the list of registered providers may be retrieved via
  the {@link Security#getProviders() Security.getProviders()} method.
  
  @param algorithm the standard name of the requested MAC algorithm.
  See the Mac section in the <a href=
  "{@docRoot}openjdk-redirect.html?v=8&path=/technotes/guides/security/StandardNames.html#Mac">
  Java Cryptography Architecture Standard Algorithm Name Documentation</a>
  for information about standard algorithm names.
  
  @param provider the name of the provider.
  
  @return the new <code>Mac</code> object.
  
  @exception NoSuchAlgorithmException if a MacSpi
  implementation for the specified algorithm is not
  available from the specified provider.
  
  @exception NoSuchProviderException if the specified provider is not
  registered in the security provider list.
  
  @exception IllegalArgumentException if the <code>provider</code>
  is null or empty.
  
  @see java.security.Provider