code: public static ServletContextCache getCache(ServletContext servletContext) {
  		ServletContextCache cache = (ServletContextCache)servletContext.getAttribute(ATTRIBUTE_KEY);
  		if(cache == null) {
  			// It is possible this is called during context initialization before the listener
  			cache = new ServletContextCache(servletContext);
  			servletContext.setAttribute(ATTRIBUTE_KEY, cache);
  			//throw new IllegalStateException("ServletContextCache not active in the provided ServletContext.  Add context listener to web.xml?");
  		} else {
  			assert cache.servletContext == servletContext;
  		}
  		return cache;
  	}
docs: Gets or creates the cache for the provided servlet context.