@Override
 protected String multipleEventMessage() {
   return String.format(
       multipleEventMessageTemplate,
       user.getName(),
       getEventOccurrenceCount() - 1,
       ellipsis(content.getTitle(), 30));
 }
 @Override
 public String getUrl() {
   return String.format(urlTemplate, content.getId());
 }
 @Override
 public Long pkAtBelongTypeTable() {
   return content.getId();
 }
 @Override
 protected String singleEventMessage() {
   return String.format(singleEventMessageTemplate, user.getName(), content.getTitle());
 }