code: @Override
  	public void setAggregator(IAggregator aggregator) {
  		this.aggregator = aggregator;
  		// get the file resource factory
  		Iterable<IAggregatorExtension> iter = aggregator.getExtensions(IResourceFactoryExtensionPoint.ID);
  		for (IAggregatorExtension ext : iter) {
  			if ("file".equals(ext.getAttribute("scheme"))) { //$NON-NLS-1$ //$NON-NLS-2$
  				fileResourceFactory = (IResourceFactory)ext.getInstance();
  				break;
  			}
  		}
  		if (fileResourceFactory == null) {
  			throw new IllegalStateException("Missing file resource factory"); //$NON-NLS-1$
  		}
  	}
docs: /* (non-Javadoc)
  @see com.ibm.jaggr.core.impl.cache.GenericCacheImpl#setAggregator(com.ibm.jaggr.core.IAggregator)