gistfile1.txt

 /**
   * Recursive method that returns a Future of URLs
   * 
   * @param url
   * @param maxDepth
   * @param currentDepth
   * @return
   */
  public Future<List<String>> crawl(final String url, final int maxDepth, final int currentDepth) {
    
    if (maxDepth == currentDepth) {
      return Futures.future(new Callable<List<String>>() {
        @Override
        public List<String> call() throws Exception {
          return Collections.emptyList();
        }
      }, ec);
    }
    else {
      // 1. 
      Future<List<String>> crawlResultsFuture = future(new Callable<List<String>>() {
        public List<String> call() throws Exception {
          Collection<String> foundUrls = MockWebCrawler.crawl(url)
          return Arrays.asList(foundUrls.toArray(new String[0]));
        }
      }, ec);
      
      // 2. 
      Future<Iterable<List<String>>> childCrawlsFuture = crawlResultsFuture.flatMap(new Mapper<List<String>, Future<Iterable<List<String>>>>() {
        public Future<Iterable<List<String>>> apply(final List<String> foundUrls) {
          List<Future<List<String>>> crawlFutures = new ArrayList<Future<List<String>>>();
          crawlFutures.add(Futures.successful(foundUrls, ec));
          for (String u : foundUrls) {
            Future<List<String>> crawlFuture = crawl(u, maxDepth, currentDepth + 1);
            crawlFutures.add(crawlFuture);
          }
          return Futures.sequence(crawlFutures, ec);
        }
      });
      
      // 3. 
      Future<List<String>> crawlFuture = childCrawlsFuture.map(new Mapper<Iterable<List<String>>, List<String>>() {
        @Override
        public List<String> apply(Iterable<List<String>> childCrawls) {
          List<String> result = new ArrayList<String>();
          for (List<String> c : childCrawls) {
            result.addAll(c);
          }
          return result;
        }
      });
      return crawlFuture;
    }
  }