code: public void addExternalCacheAdapter(String groupId, String address, String beanName) throws DynamicCacheServiceNotStarted {
      	if (servletCacheUnit == null) {
      		throw new DynamicCacheServiceNotStarted("Servlet cache service has not been started."); 
      	}
      	servletCacheUnit.addExternalCacheAdapter(groupId, address, beanName);
      }
docs: This implements the method in the CacheUnit interface.
  This is delegated to the ExternalCacheServices.
  It calls ServletCacheUnit to perform this operation.
  
  @param groupId The external cache group id.
  @param address The IP address of the target external cache.
  @param beanName The bean name (bean instance or class) of
  the ExternalCacheAdaptor that can deal with the protocol of the
  target external cache.