Java 8 list to nested map

Question

I hava a list of Class A like

class A {
 private Integer keyA;
 private Integer keyB;
 private String text;
}

I want to transfer <

Answer 1

Seems that you just need a cascaded groupingBy:

Map<Integer, Map<Integer,List<A>>> aMappedByKeyAAndKeyB = aList.stream()
    .collect(Collectors.groupingBy(A::getKeyA, 
                 Collectors.groupingBy(A::getKeyB)));