Reduce 2D collection in Java 8

gistfile1.java

Map<String, List<Field>> fieldmap = new HashMap<>();
fieldmap.put("f1", Arrays.asList(new Field("f_str"), new Field("f_abc")));
fieldmap.put("f2", Arrays.asList(new Field("f_int")));

// This is the best I came up with
List<String> names = fieldmap.values().stream().collect(
                ArrayList<String>::new,
                (l, fs) -> l.addAll(fs.stream().map(Field::getName).collect(toList())),
                ArrayList<String>::addAll);