/**
* Now is time to join on the tweetId to get a stream of triples (tweetId, hashtag, url).
*
*/
topology.join(hashtags, new Fields("tweetId"), urls, new Fields("tweetId"), new Fields("tweetId", "hashtag", "url"))
.each(new Fields("tweetId", "hashtag", "url"), new Print());
return topology.build();
}