question: public Builder addListenUrls ( List < String > urls ) { List < String > needAdd = new ArrayList < String > ( ) ; for ( String url : urls ) { if ( ! UrlUtil . isUrl ( url ) ) { continue ; } needAdd . add ( url ) ; } if ( ! CollectionUtil . isEmpty ( needAdd ) ) { if ( mListenUrls == null ) { mListenUrls = new HashSet < String > ( ) ; } mListenUrls . addAll ( needAdd ) ; } return this ; }
target:  add the urls for listening