Converting a collection to Map by sorting it using java 8 streams

问题

I have a list that I need to custom sort and then convert to a map with its Id vs. name map.

Here is my code:

Map<Long, String> map = new LinkedHashMap<>();
list.stream().sorted(Comparator.comparing(Building::getName)).forEach(b-> map.put(b.getId(), b.getName()));

I think this will do the job but I wonder if I can avoid creating LinkedHashMap here and use fancy functional programming to do the job in one line.

回答1:

You have Collectors.toMap for that purpose :

Map<Long, String> map = 
    list.stream()
        .sorted(Comparator.comparing(Building::getName))
        .collect(Collectors.toMap(Building::getId,Building::getName));

If you want to force the Map implementation that will be instantiated, use this :

Map<Long, String> map = 
    list.stream()
        .sorted(Comparator.comparing(Building::getName))
        .collect(Collectors.toMap(Building::getId,
                                  Building::getName,
                                  (v1,v2)->v1,
                                  LinkedHashMap::new));

回答2:

Use toMap() of java.util.stream.Collectors

来源：https://stackoverflow.com/questions/29721095/converting-a-collection-to-map-by-sorting-it-using-java-8-streams