code: public static <T> T loadUniqueServiceProvider( Class<T> klass )
      {
          List<T> providers = findServiceProviders( klass );
          if( providers.isEmpty() )
          {
              throw new NoServiceProviderException( klass.getName()
                      + ": no service provider found in META-INF/services on classpath" );
          }
          else if( providers.size() > 1 )
          {
              throw new NonUniqueServiceProviderException( klass.getName()
                      + ": multiple service providers found in META-INF/services on classpath" );
          }
          return providers.get( 0 );
      }
docs: Returns the unique service provider for a given service and throws an exception if there
  is no unique provider
  
  @param klass service interface or class
  @return the first provider found
  @throws NoServiceProviderException
  @throws NonUniqueServiceProviderException