Java 8流从列表中的Map读取值

Question

I do not want to use foreach and loop. I want to use stream in Java 8 to find value in Map inside List

List<Map<String, Boolean>> types = ...

map.stream().filter(...

problem is that in filter I can not search by key/value pair.

I want to get all elements with boolean = true

I am doing something wrong?

Answer 1

Stream over the entry set:

types.stream()                               // stream of maps
    .flatMap(map -> map.entrySet().stream()) // flat map to stream of map entries
    .filter(Map.Entry::getValue)             // filter for value == true
    .map(Map.Entry::getKey)                  // get the key
    .collect(Collectors.toList());           // collect

You can remove .map(Map.Entry::getKey) if you'd rather end up with a list of key/value pairs.

Answer 2

    List<Map<String, Boolean>> types = new ArrayList<>();

    Map<String, Boolean> myMap = new HashMap<>();
    Map<String, Boolean> myMap2 = new HashMap<>();

    myMap2.put("Meric", true);
    myMap2.put("BERBER", false);
    types.add(myMap2);

    myMap.put("TEST1", true);
    myMap.put("TEST2", false);
    types.add(myMap);


    types.stream()
            .flatMap(map -> map.entrySet().stream())
            .filter(Map.Entry::getValue)
            .map(Map.Entry::getKey)
            .forEach(System.out::println);

and output will be

 Meric
 TEST1