I've an object,
class Object2{
String name;
String id;
Map<String, String> customData;
}
class Object1{
List<Object2> obj1List;
}
I want to convert this customData Map in the List of object1 into one single map, I am ok with over-writing the values if the key already exists.
Here's a way with lambdas and Java 8:
Map<String, String> map = new LinkedHashMap<>();
object1List.forEach(o1 ->
o1.getObject1List().forEach(o2 -> map.putAll(o2.getCustomData())));
getObject1List()Use flatMap and toMap as follows:
List<Object1> source = ...
Map<String, String> result =
source.stream()
.flatMap(e -> e.getObj1List().stream()
.flatMap(a -> a.getCustomData().entrySet().stream()))
.collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));
or if you're dealing with a single Object1 object:
Object1 myObj = ...
Map<String, String> result =
myObj.getObj1List()
.stream()
.flatMap(a -> a.getCustomData().entrySet().stream())
.collect(toMap(Map.Entry::getKey, Map.Entry::getValue, (l, r) -> r));
Alternatively, you can perform Stream.flatMap and then use Map.putAll as
List<Object1> object1s = new ArrayList<>(); // initialise as you would
Map<String, String> finalCustomData = new LinkedHashMap<>();
object1s.stream() // Stream<Object1>
.flatMap(o1 -> o1.getObj1List().stream()) // Stream<Object2>
.map(Object2::getCustomData) // Stream<Map<String, String>>
.forEach(finalCustomData::putAll);
