Sort the values (Set -> SortedSet) of the Map with Java 8 Streams

Question

如何使用流对Map<String, Set<String>>值进行排序Map<String, Set<String>>即转换为Map<String, SortedSet<String> >？

Answer 1

Just iterate over each entry and convert the Set<T> (eg HashSet<T> ) to a SortedSet<T> (eg TreeSet<T> ) as:

Map<String, Set<String>> input = new HashMap<>();
Map<String, SortedSet<String>> output = new HashMap<>();
input.forEach((k, v) -> output.put(k, new TreeSet<>(v)));

or with streams as:

Map<String, Set<String>> input = new HashMap<>();
Map<String, SortedSet<String>> output = input.entrySet().stream()
        .collect(Collectors.toMap(Map.Entry::getKey, a -> new TreeSet<>(a.getValue())));