I have Map<String, Object> which has to be become Map<String, String>. Filtering should be done by List<String>.
That list contains keys of map elements that should be in new map.
For this I need to use streams.
Map<String, Object> oldMap;
List<String> keysForFiltering;
Map<String, String> newMap;
It would be more efficient if the filter would operate on a Set of keys instead of a List of keys, since searching a Set is more efficient than searching a List.
Map<String, String> newMap =
oldMap.entrySet()
.stream()
.filter(e -> keysForFiltering.contains(e.getKey()))
.collect(Collectors.toMap(Map.Entry::getKey,
e -> e.getValue().toString()));
since you have a map then you can get the stream of that and use a custom predicate, that predicate need to check if the Entry.key is present in your list or not
Map<String, String> myMap = new HashMap<>();
myMap.put("A", "fortran");
myMap.put("B", "java");
myMap.put("C", "c++");
myMap.put("D", "php");
List<String> keysForFiltering = Arrays.asList("A", "C");
Predicate<Entry<String, String>> myPredicate = t -> keysForFiltering.contains(t.getKey());
Map<String, String> filteredMap = myMap
.entrySet().stream().filter(myPredicate)
.collect(Collectors.toMap(p -> p.getKey(), p -> p.getValue()));
System.out.println(filteredMap);