Model:

Year{
 int year;
}

ObjectB{
 ObjectBA bb;  <- ObjectBA{int value}
 ObjectBB ba;  <- ObjectBA{int value}
}

ObjectC{
  List<ObjectBA>
  List<ObjectBB>
}

How to convert: Map<Year, List<ObjectB>> to Map<Year, ObjectC> where Object C have all element from ObjectB

I already have:

var result = inputMap.entrySet().stream()
             .collect(Collectors.toMap(
                        e -> e.getKey(),
                        e -> e.getValue().stream().
                                map(
                                       value -> value.bb().getValue()
                                ).toList())
                );

i need something that give me multimple list in Object, like:

 map(
       new ObjectC(
          value -> value.ba().getValue(),
          value -> value.bb().getValue()
    ).toList())

CodePudding user response：

What you've got looks pretty good already. Just replace the value mapper with e -> convert(e.getValue()) where convert is like the function below that converts a List<ObjectB> into an ObjectC:

ObjectC convert(List<ObjectB> list) {
    ObjectC c = new ObjectC();
    for (ObjectB b : list) {
        c.ba.add(b.ba);
        c.bb.add(b.bb);
    }
    return c;
}

Or if you'd prefer to stick with just using streams, try Stream#collect like so:

e.getValue().stream().collect(
        () -> new ObjectC(),
        (c, b) -> {
                c.ba.add(b.ba);
                c.bb.add(b.bb);
        },
        (c1, c2) -> {
                c1.ba.addAll(c2.ba);
                c1.bb.addAll(c2.bb);
        }
)