code: protected String generateCacheKey(
          CmsObject cms,
          String targetSiteRoot,
          String detailPagePart,
          String absoluteLink) {
  
          return cms.getRequestContext().getSiteRoot() + ":" + targetSiteRoot + ":" + detailPagePart + absoluteLink;
      }
docs: Generates the cache key for Online links.
  @param cms the current CmsObject
  @param targetSiteRoot the target site root
  @param detailPagePart the detail page part
  @param absoluteLink the absolute (site-relative) link to the resource
  @return the cache key