code: public static boolean isCachedContentRequest(final Request request) {
  
  		// Get target id on request
  		String targetId = request.getParameter(Environment.TARGET_ID);
  		if (targetId == null) {
  			return false;
  		}
  
  		// Get target
  		ComponentWithContext targetWithContext = WebUtilities.getComponentById(targetId, true);
  		if (targetWithContext == null) {
  			return false;
  		}
  
  		// Check for caching key
  		WComponent target = targetWithContext.getComponent();
  		UIContextHolder.pushContext(targetWithContext.getContext());
  
  		try {
  			// TODO Look at implementing CacheableTarget interface
  			String key = null;
  			if (target instanceof WContent) {
  				key = ((WContent) target).getCacheKey();
  			} else if (target instanceof WImage) {
  				key = ((WImage) target).getCacheKey();
  			} else if (target instanceof WVideo) {
  				key = ((WVideo) target).getCacheKey();
  			} else if (target instanceof WAudio) {
  				key = ((WAudio) target).getCacheKey();
  			}
  			return !Util.empty(key);
  		} finally {
  			UIContextHolder.popContext();
  		}
  	}
docs: Check if the request is for cached content.
  
  @param request the request being processed
  @return true if content is cached, otherwise false